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The addition of metal oxide nanoparticles (NPs) to microalgae cultures have become of great interest since they can directly and/or indirectly interact with microalgae resulting in enhanced production of biomass and high-value added products. The physicochemical characteristics of the NPs, i.e., crystal phase, can differently influence microalgae metabolism, thus the synthesis of optimal NPs is mandatory to improve the value of microalgae biomass.This study aimed at assessing the effect of Fe2O3 NPs on Chlorella spp. cultures with and without carbonate supplementation to confirm their beneficial effect. First, Fe2O3 NPs were synthetized and two different annealing temperatures were implemented, 450 °C (Fe2O3-450) and 1000 °C (Fe2O3-1000), to obtain Fe2O3 NPs with different crystal phases. The NPs crystal phase was analyzed by X-ray diffraction and the presence of the γ- and α- phases on both NPs were confirmed. However, the Fe2O3-450 NPs presented a higher content of the γ- phase. Subsequently, the effect of the crystal phase of Fe2O3 NPs was assessed in Chlorella spp. cultures. The addition of Fe2O3-1000 NPs resulted in inhibition of Chlorella spp. On the other hand, the addition of Fe2O3-450 NPs recorded the carbohydrate enhancements > 91% in Chlorella spp. cultures. The indirect effect of the synthetized NPs was assessed in microalgae cultures without carbonate supplementation and the same tendency was observed. This study proves that Fe2O3-450 NPs directly and indirectly interact with microalgae, and can be used as a strategy to produce high-value biomass even in environments without carbonate supplementation. [ABSTRACT FROM AUTHOR]

Microalgae cultures have emerged as a promising strategy in diverse areas, ranging from wastewater treatment to biofuel production, thus contributing to the search for carbon neutrality. These photosynthetic organisms can utilize the resources present in wastewater and fix atmospheric CO 2 to produce biomass with high energy potential. In this study, the removal efficiency of Polycyclic Aromatic Hydrocarbons (PAHs), CO 2 fixation and lipid content in the biomass produced from microalgae grown in airlift photobioreactor were evaluated. Four mesoscale cultures were carried out: Control (Seawater + Conway medium), Treatment A (Oil Produced Water + Poultry Effluent Water), Treatment B (Poultry Effluent Water + Seawater) and Treatment C (Oil Produced Water, Seawater and nutrients). The impact of biostimulation, through the addition of nutrients, on PAHs removal efficiency (up to 90%), CO 2 fixation rate (up to 0.20 g L -1 d -1 ) and the composition of the generated biomass was observed. Primarily, the addition of nitrates to the culture medium impacted CO 2 fixation rate of the microalgae. In addition, a direct correlation was observed between PAHs removal and lipid accumulation in the biomass, up to 36% in dry weight, demonstrating microalgae's ability to take advantage of the organic carbon (PAHs) present in the culture medium to generate lipid-rich biomass. The concentration of polysaccharides in the biomass obtained did not exceed 12% on a dry weight basis, and the Higher Heating Value (HHV) ranged between 17 and 21 MJ kg -1 . Finally, the potential of generating hydrogen through pyrolysis was highlighted, taking advantage of the characteristics of biomass as a conversion route to produce biofuels. These results show that microalgae are effective in wastewater treatment and have great potential in producing biofuels, thus contributing to the transition towards more sustainable energy sources and climate change mitigation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Aquaculture farming generates a significant amount of wastewater, which has prompted the development of creative bioprocesses to improve wastewater treatment and bioresource recovery. One promising method of achieving these aims is to directly recycle pollutants into microbe-rice bran complexes, which is an economical and efficient technique for wastewater treatment that uses synergetic interactions between algae and bacteria. This study explores novel bioaugmentation as a promising strategy for efficiently forming microbial-rice bran complexes in unsterilized aquaculture wastewater enriched with agricultural residues (molasses and rice bran). Results found that rice bran serves a dual role, acting as both an alternative nutrient source and a biomass support for microalgae and bacteria. Co-bioaugmentation, involving the addition of probiotic bacteria (Bacillus syntrophic consortia) and microalgae consortiums (Tetradesmus dimorphus and Chlorella sp.) to an existing microbial community, led to a remarkable 5-fold increase in microbial-rice bran complex yields compared to the non-bioaugmentation approach. This method provided the most compact biofloc structure (0.50 g/L) and a large particle diameter (404 μm). Co-bioaugmentation significantly boosts the synthesis of extracellular polymeric substances, comprising proteins at 6.5 g/L and polysaccharides at 0.28 g/L. Chlorophyta, comprising 80% of the total algal phylum, and Proteobacteria, comprising 51% of the total bacterial phylum, are emerging as dominant species. These microorganisms play a crucial role in waste and wastewater treatment, as well as in the formation of microbial-rice bran complexes that could serve as an alternative aquaculture feed. This approach prompted changes in both microbial community structure and nutrient cycling processes, as well as water quality. These findings provide valuable insights into the transformative effects of bioaugmentation on the development of microbial-rice bran complexes, offering potential applications in bioprocesses for waste and wastewater management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Microalgae have gained considerable attention as promising candidates for precision nutrition and dietary regulation due to their versatile metabolic capabilities. This review innovatively applies system metabolic engineering to utilize microalgae for precision nutrition and sustainable diets, encompassing the construction of microalgal cell factories, cell cultivation and practical application of microalgae. Manipulating the metabolic pathways and key metabolites of microalgae through multi-omics analysis and employing advanced metabolic engineering strategies, including ZFNs, TALENs, and the CRISPR/Cas system, enhances the production of valuable bioactive compounds, such as omega-3 fatty acids, antioxidants, and essential amino acids. This work begins by providing an overview of the metabolic diversity of microalgae and their ability to thrive in diverse environmental conditions. It then delves into the principles and strategies of metabolic engineering, emphasizing the genetic modifications employed to optimize microalgal strains for enhanced nutritional content. Enhancing PSY, BKT, and CHYB benefits carotenoid synthesis, whereas boosting ACCase, fatty acid desaturases, and elongases promotes polyunsaturated fatty acid production. Here, advancements in synthetic biology, evolutionary biology and machine learning are discussed, offering insights into the precision and efficiency of metabolic pathway manipulation. Also, this review highlights the potential impact of microalgal precision nutrition on human health and aquaculture. The optimized microalgal strains could serve as sustainable and cost-effective sources of nutrition for both human consumption and aquaculture feed, addressing the growing demand for functional foods and environmentally friendly feed alternatives. The tailored microalgal strains are anticipated to play a crucial role in meeting the nutritional needs of diverse populations and contributing to sustainable food production systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This review comprehensively examines the various applications of microalgae, focusing on their significant potential in producing biodiesel and hydrogen, serving as sustainable food sources, and their efficacy in treating both municipal and food-related wastewater. While previous studies have mainly focused on specific applications of microalgae, such as biofuel production or wastewater treatment, this review covers these applications comprehensively. It examines the potential for microalgae to be applied in various industrial sectors such as energy, food security, and environmental management. By bridging these different application areas, this review differs from previous studies in providing an integrated and multifaceted view of the industrial applications of microalgae. Since it is essential to increase the productivity of the process to utilize microalgae for various industrial applications, research trends in different microalgae cultivation processes, including the culture system (e.g., open ponds, closed ponds) or environmental conditions (e.g., pH, temperature, light intensity) to improve the productivity of biomass and valuable substances was firstly analyzed. In addition, microalgae cultivation technologies that can maximize the biomass and valuable substances productivity while limiting the potential for contamination that can occur when utilizing these systems have been described to maximize CO 2 reduction. In conclusion, this review has provided a detailed analysis of current research findings and technological innovations, highlighting the important role of microalgae in addressing global challenges related to energy, food supply, and waste management. It has also provided valuable insights into future research directions and potential commercial applications in several bio-related industries, and illustrated how important continued exploration and development in this area is to realize the full potential of microalgae., Competing Interests: Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Conflicts of interest There are no conflicts of interest to declare. Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

Background: Microalgae have emerged as sustainable alternatives to fossil fuels and high-value petrochemicals. Despite the commercial potential of microalgae, their low biomass productivity is a significant limiting factor for large-scale production. In the photoautotrophic cultivation of microalgae, achievable cell density levels depend on the light transmittance of the production system, which can significantly decrease the photosynthetic rate and biomass production. In contrast, the mixotrophic cultivation of microalgae using heterotrophic carbon sources enables high-density cultivation, which significantly enhances biomass productivity. The identification of optimal production conditions is crucial for improving biomass productivity; however, it is typically time- and resource-consuming. To overcome this problem, high-throughput screening (HTS) system presents a practical approach to maximize biomass and lipid production and enhance the industrial applicability of microalgae., Results: In this study, we proposed a two-step HTS assay that allows effective screening of heterotrophic conditions compatible with new microalgal isolates. To confirm the effectiveness of the HTS assay, three microalgal isolates with distinctive morphological and genetic traits were selected. Suitable cultivation conditions, including various heterotrophic carbon sources, substrate concentrations, and temperatures, were investigated using a two-step HTS assay. The optimized conditions were validated at the flask scale, which confirmed a significant enhancement in the biomass and lipid productivity of each isolate. Moreover, the two-step HTS assay notably enhanced economic and temporal efficiency compared to conventional flask-based optimization., Conclusions: These results suggest that our two-step HTS assay is an efficient strategy for investigating and optimizing microalgal culture conditions to maximize biomass and lipid productivity. This approach has the potential to enhance the industrial applicability of microalgae and facilitate the seamless transition from laboratory to field applications., (© 2024. The Author(s).)

Aquaculture operations produce large amounts of wastewater contaminated with organic matter, nitrogenous compounds, and other emerging contaminants; when discharged into natural water bodies, it could result in ecological problems and severely threaten aquatic habitats and human health. However, using aquaculture wastewater in biorefinery systems is becoming increasingly crucial as advancements in valuable bioproduct production continue to improve economic feasibility. Research on utilising microalgae as an alternative to producing biomass and removing nutrients from aquaculture wastewater has been extensively studied over the past decades. Microalgae have the potential to use carbon dioxide (CO 2 ) effectively and significantly reduce carbon footprint, and the harvested biomass can also be used as aquafeed. Furthermore, aquaculture wastewater enriched with phosphorus (P) is a potential resource for P recovery for the production of biofertiliser. This will reduce the P supply shortage and eliminate the environmental consequences of eutrophication. In this context, the present review aims to provide a comprehensive overview of the current state of the art in a generation, as well as the characteristics and environmental impact of aquaculture wastewater reported by the most recent research. Furthermore, the review synthesized recent developments in algal biomass cultivation using aquaculture wastewater and its utilisation as biorefinery feedstocks for producing value-added products, such as aquafeeds, bioethanol, biodiesel, biomethane, and bioenergy. This integrated process provides a sustainable method for recovering biomass and water, fully supporting the framework of a circular economy in aquaculture wastewater treatment via resource recovery., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Bisphenols (BPs) are recognized as endocrine disrupting compounds and have garnered increasing attention due to their widespread utilization. However, the varying biological toxicities and underlying mechanisms of BPs with different functional groups remain unknown. In the present study, the toxic effects of four BPs (BPA, BPS, BPAF, and TBBPA) on a photosynthetic microalgae Chromochloris zofingiensis were compared. Results showed that halogen-containing BPs exhibited higher cellular uptake, leading to more severe oxidative stress, lower photosynthetic efficiency, and greater accumulation of starch and lipids. Specifically, TBBPA with bromine groups showed a greater toxicity than BPAF with fluorine groups, possibly due to the incomplete debromination in C. zofingiensis. Transcriptomic analysis revealed that halogen-containing BPs triggered greater number of differentially expressed genes (DEGs), and only 64 common DEGs were found among different BPs, indicating that the effects of BPs with different functional groups varied greatly. Genes involved in endocytosis, peroxisomes, and endoplasmic reticulum protein processing pathways were mostly upregulated across different BPs, while photosynthesis-related genes showed varied expression, possibly due to their distinct functional groups. Additionally, SIN3A, ZFP36L, CHMP, and ATF2 emerged as potential key regulatory genes. Overall, this study thoroughly explained how functional groups impact the toxicity and biodegradation of BPs in C. zofingiensis., Competing Interests: Declaration of Competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Microalgae-bacteria consortia (MBC) system has been shown to enhance the efficiency of microalgae in wastewater treatment, yet its effectiveness in treating levofloxacin (LEV) wastewater remains unexplored. This study compared the treatment of LEV wastewater using pure Chlorella pyrenoidosa (PA) and its MBC constructed with activated sludge bacteria. The results showed that MBC improved the removal efficiency of LEV from 3.50-5.41 % to 33.62-57.20 % by enhancing the growth metabolism of microalgae. The MBC increased microalgae biomass and extracellular polymeric substance (EPS) secretion, yet reduced photosynthetic pigment content compared to the PA. At the phylum level, Proteobacteria and Actinobacteriota are the major bacteria in MBC. Furthermore, the transcriptome reveals that the growth-promoting effects of MBC are associated with the up-regulation of genes encoding the glycolysis, the citrate cycle (TCA cycle), and the pentose phosphate pathway. Enhanced carbon fixation, coupled with down-regulation of photosynthetic electron transfer processes, suggests an energy allocation mechanism within MBC. The up-regulation of porphyrin and arachidonic acid metabolism, along with the expression of genes encoding LEV-degrading enzymes, provides evidence of MBC's superior tolerance to and degradation of LEV. Overall, these findings lead to a better understanding of the underlying mechanisms through which MBC outperforms PA in treating LEV wastewater., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Infectious diseases have significantly shaped human history, leading to significant advancements in medical science. The discovery and development of antibiotics represented a critical breakthrough, but the rise of antibiotic-resistant pathogens now presents a serious global health threat. Due to the limitations of current synthetic antimicrobials, such as toxicity and environmental concerns, it is essential to explore alternative solutions. Algae, particularly microalgae and cyanobacteria, have emerged as promising sources of bioactive antimicrobial compounds. This review provides a comprehensive analysis of the antimicrobial properties of algal-derived compounds, including polysaccharides, fatty acids, and phenols, which have shown effectiveness against multi-drug-resistant bacteria. A co-occurrence bibliometric analysis using VOSviewer highlighted five key research clusters: antibiotic resistance, algal extracts, biosynthesis, water treatment, and novel pharmacological compounds. Furthermore, the primary mechanisms of action of these bioactive compounds, such as the inhibition of protein synthesis and cell membrane disruption, were identified, demonstrating their potential against both common and multi-resistant pathogens. Future research should prioritize optimizing algal biomass production, utilizing genetic and metabolic engineering, and creating innovative delivery systems to enhance the efficient production of bioactive compounds.

Rice straw (RS) is a widely available agricultural residue with significant potential for biogas production and feed applications; however, its poor digestibility and nutritional value limit its utilization. This study explores an innovative approach to enhance the digestibility and nutritional value of RS by cultivating Chlorella vulgaris through immobilization technology on RS, using liquid manure (LM) as an alternative to the traditional BG11 medium. The results showed an increase in chlorophyll a (Chl a) after 12 days for both the BG11 medium and LM-based treatments, from 0.13 to 0.34 and 0.24 mg Chl a /g product (DM) , respectively. Additionally, the immobilized microalgal biomass increased to 284.18 and 170.14 mg algal biomass /g product (DM) , respectively. Soaking under microaerobic conditions during cultivation led to the partial degradation of RS. This, combined with the formed microalgal biofilm, contributed to an improved digestibility of the dry matter, reaching 69.1% and 65.9% for the final products based on the BG11 medium and LM mediums, respectively, compared to 52.1% for the raw RS. Furthermore, the crude protein and lipids contents were significantly improved with the potential for applications in feed, reaching 21.4% and 4.1% for the BG11 medium-based product, while they were observed to be 12.8% and 3.0%, respectively, for the LM-based product. Additionally, carbon-to-nitrogen ratio was significantly reduced compared to the raw RS. The higher digestibility and improved nutritional value contributed to increased biogas production, reaching 129.3 and 118.7 mL/g (TS) for the products based on the traditional medium and LM medium, respectively, compared to 86.7 mL/g (TS) for the raw RS. The immobilization mechanism and biofilm development could be attributed to the roughness of the RS and extracellular polymer substances. This study demonstrates that integrating C. vulgaris cultivation on RS with LM as a nutrient source not only enhances the digestibility and nutritional value of RS but also offers a sustainable waste management solution with potential applications in biogas production and animal feed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Municipal wastewater (MW) and industrial wastewater from juice processing (IWJ) were blended in different proportions to assess the effect of the carbon/nitrogen (C/N) ratio on pollutant removal, microalgal biomass (MB) cultivation, and the accumulation of carotenoids and biocompounds. MB development was not observed in treatments with higher C/N ratios (>30.67). The wastewater mixture favored the removal of dissolved organic carbon (75.61 and 81.90%) and soluble chemical oxygen demand (66.78-88.85%), compared to the treatment composed exclusively of MW (T7). Treatments T3 and T6 (C/N ratio equal to 30.67 and 7.52, respectively) showed higher Chlorophyll-a concentrations, 1.47 and 1.54 times higher than T7 (C/N ratio 1.75). It was also observed that the C/N ratio of 30.67 favored the accumulation of carbohydrates and lipids (30.07% and 26.39%, respectively), while the C/N ratio of 7.52 improved protein accumulation (33.00%). The fatty acids C16:0, C18:1, C18:2, and C18:3 had the highest concentrations. Additionally, increasing the C/N ratio can be an efficient strategy to improve the production of fatty acids for biofuels, mainly due to the increased concentration of shorter-chain fatty acids (C16:0). These findings suggest that blending wastewater not only enhances treatment performance but also increases the accumulation of valuable carbohydrates and lipids in MB, and optimizes fatty acid production for biofuel applications. This research represents significant progress towards feasibility of using MB produced from wastewater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

To improve denitrification efficiency of microalgal-bacterial aggregates (MABAs) when treating low carbon to nitrogen (C/N) ratio wastewater, CK (the biological control), C1 (untreated corncobs), C2 (alkali-treated corncobs), CFe1 (C1 loaded iron nanoparticles) and CFe2 (C2 loaded iron nanoparticles) five groups of experiments were installed under artificial light (1600 lm). After 36 h of experiment, NO 3 - -N was almost completely converted in CFe1 following by CFe2 when the initial concentration was 60.1 mg/L, whose NO 3 - -N conversion rates were 6.2 and 3.4 times faster than the CK group, respectively. The result showed that the corncobs-loaded iron nanoparticles (CFe1, CFe2) had the potential to promote denitrification process and the CFe1 was more effective. Meanwhile, the CFe1 and CFe2 resulted in a decreased content in extracellular polymeric substances (EPS) secretion because iron nanoparticles (Fes) promoted electron transport and alleviated the nitrate stress. Moreover, the electrochemical analysis of EPS showed that the corncobs and corncobs-loaded iron nanoparticles improved the electron transport rate and redox active substances production. The increase in electron transport activity (ETSA), adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH) also indicated that the CFe1 and CFe2 promoted microbial metabolic activity and the electron transport rate in MABAs. In addition, the CFe1 group enhanced the enrichment of Proteobacteria, Patescibacteria, Chlorophyta and Ignavibacteriae, which was contributed to the nitrogen removal performance of MABAs. In summary, the enhancement mechanism of corncobs-loaded iron nanoparticles on denitrification process of MABAs was depicted through EPS secretion, electrochemical characteristics, microbial metabolic activity and microbial community. The article provides a viable program for enhancing the denitrification performance of MABAs when treating low C/N wastewater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Tidal flats are inhabited by benthic microalgae (microphytobenthos, MPB) supporting important ecosystem functions and services. Studies on MPB have been conducted mainly in temperate systems, despite that the majority of tidal flats on Earth are found in the tropical zone (∼55%). To fill this gap of knowledge and evaluate the contribution of tidal flat MPB in one of the most productive estuaries worldwide, sediment cores were collected from 14 stations along the inner Gulf of Nicoya (Costa Rica) at different tidal heights or sea levels (SL) from October 2013 to April 2014. MPB abundance, using chlorophyll a (Chla) biomass as a proxy, and net primary production (P N ) and dark respiration (R D ), using O 2 microsensors, were measured together with other sediment biogeochemical variables in muddy and sandy sediments. Landsat-8 satellite images were used to map the extension of tidal flats and the abundance of MPB using Normalized Difference Vegetation Index (NDVI) as a proxy. Chla ranged from 0.45 to 7.45 μg cm -2 , with higher concentrations observed closer to the river mouth. There was no significant correlation between Chla and SL nor with any other sediment physicochemical variable. MPB abundance estimated by remote sensing displayed considerable spatial heterogeneity, both within and among tidal flats, and clear seasonal differences with higher abundance during the rainy season. P N ranged between 0.8 and 8.6 mmol O 2 m -2 h -1 , being positively correlated to SL and to the accumulated rain during 30 days prior to the sampling date and inversely to the mean irradiance at noon during the previous month. Daily net community metabolism estimated from P N and R D data and converted to carbon fixation rates indicates that the unvegetated tidal flats of the gulf contribute as much as the total input of allochthonous C from the Tempisque River. However, the results presented here have to be confirmed with direct measurements of C transfer, including the contribution of the adjacent mangrove system. Such studies are crucial to assess the local, regional and global importance of production and other ecosystem services by MPB in tropical areas., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Alfonso Corzo reports financial support was provided by Spanish Ministry of Economy and Competitiveness. Alfonso Corzo reports financial support was provided by Spanish International Development Cooperation Agency. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The escalating occurrence of the antibiotic Sulfamethoxazole (SMX) in the environment presents a significant global threat to ecological systems and human health. Despite the growing interest in using microalgae for antibiotic biodegradation, strategies to enhance SMX elimination remain underexplored. In this study, we isolated a novel aggregation-algae consortium (AAC) from a municipal wastewater treatment plant (WWTP) and examined its potential for SMX removal, optimized culture conditions, SMX metabolite fate and the physicochemical impact on microalgal cells. The findings revealed that the AAC demonstrated remarkable resistance to SMX, even at concentrations as high as 10 mg/L, and could degrade SMX via free radical reactions. Although ion repulsion limited the biodegradation of AAC, the addition of peptone and yeast extract resulted in a significant enhancement, increased by 16.71%, 39.12% and 46.77% of three SMX groups. Moreover, AAC exhibited exceptional adaptability in real wastewater, achieving removal of 87.05%, 97.39% and 20.80% for total dissolved nitrogen, total dissolved phosphorus and SMX, respectively. The decreased degradation toxicity of SMX following AAC treatment was further validated by ECOSAR software and in vitro tests using Caenorhabditis elegans. This study advanced our understanding of SMX biodegradation and provided a novel approach for treating wastewater contaminated with SMX., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The feasibility of microalgae-based biofuel production is still unclear due to the high cost and energy consumption. In order to be competitive with traditional fuels, the price per unit biofuel produced should be reduced by improving microalgal cells quality for higher biofuels productivity as well as enhancing microalgae other advantages such as wastewater treatment (WWT) and CO 2 bio-fixation. In this research, the synergistic effect of iron (Fe) and zinc (Zn) addition to municipal wastewater (MWW) on Chlorella sorokiniana Pa.91 performance was investigated in terms of biomass productivity, WWT, bio-products generation and biofuel quality. According to the result, maximum biomass concentration of 1.1, 1.49, 1.36 and 1.9 mg/L were achieved after 10 days C. sorokiniana cultivation in MWW before and after addition of Fe (9 mg/L), Zn (1 mg/L) and combined Zn/Fe (6/0.5 mg/L), respectively. It was observed that the nutrients uptake ability of microalgal cells improved by pre-treatment with Fe/Zn, as the mass balance of COD, NH 4 and PO 4 3- increased from 104.5, 13.6 and 2.9 to 111.6, 16.6 and 3.78 mg per 1 g C. sorokiniana, respectively. By adding Fe/Zn, the lipid content increased from 25 to 33 % CDW, while, no significant changes were observed in the protein and carbohydrate content. The results revealed that the fatty acid composition (i.e. SFA and MUFA content) and biofuel quality of C. sorokiniana remarkability enhanced after Fe/Zn supplementation. Overall, our finding suggested that MWW enrichment with combined Fe and Zn at an appropriate dosage is a promising approach for improving microalgae performance in particular increasing biofuel production quantity and quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The widespread use of non-ionic surfactant nonylphenol (NP) has led to significant water pollution, posing a threat to both ecological stability and human health. However, the efficient biodegradation method and system of NP-biodegradation remain complex scientific challenges. In this study, we isolated and characterized three Pseudomonas sp. strains SW-1 (Scenedesmus quadricauda-associated), ZL-2 (Ankistrodesmus acicularis-associated), XQ-3 (Chlorella vulgaris-associated), and one NP-degrading Cupriavidus sp. strain EB-4, which exhibited the ability to utilize NP as the sole carbon source. Furthermore, four consortiums of microalgae-bacterial, S. quadricauda and SW-1 (S-SW), A. acicularis and ZL-2 (A-ZL), C. vulgaris and XQ-3 (C-XQ), S. quadricauda and EB-4 (S-EB), were constructed to investigate their biodegradability and kinetic characteristics of NP degradation from water. The consortiums showed higher degradation efficiency compared to individual microalgae or bacteria. The C-XQ consortium exhibited the highest degradation rate, removing over 94% of NP within just seven days. The first-order model with the following order of degradation rate by consortiums was C-XQ (0.3960 d -1 ) > S-SW (0.3506 d -1 ) > A-ZL (0.1968 d -1 ) > S-EB (0.1776 d -1 ). Compared with the results of our previous study, the interaction between microalgae and bacteria is not a simple additive relationship. Our findings highlight the potential of an algal-bacterial consortium for the remediation of NP-contaminated environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Nannochloropsis oceanica is an industrially relevant marine microalga rich in eicosapentaenoic acid (EPA, a valuable ω-3 polyunsaturated fatty acid), yet the algal production potential remains to be unlocked. Here we engineered N. oceanica to synthesize the high-value carotenoid astaxanthin independent of high-light (HL) induction for achieving multifaceted benefits. By screening β-carotenoid ketolases and hydroxylases of various origins, and strategically manipulating compartmentalization, fusion patterns, and linkers of the enzyme pair, a remarkable 133-fold increase in astaxanthin content was achieved in N. oceanica. Iterative metabolic engineering efforts led to further increases in astaxanthin synthesis up to 7.3 mg g -1 , the highest reported for microalgae under nonstress conditions. Astaxanthin was found in the photosystem components and allowed the alga HL resistance and augmented EPA production. Besides, we achieved co-production of astaxanthin and EPA by the engineered alga through a fed-batch cultivation approach. Our findings unveil the untapped potential of N. oceanica as a robust, light-driven chassis for constitutive astaxanthin synthesis and provide feasible strategies for the concurrent production of multiple high-value biochemicals from CO 2 , thereby paving the way for sustainable biotechnological applications of this alga., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Microalgal tolerance to emerging contaminants (ECs) such as 1,4 dioxane (DXN) and its impact on phycoremediation performance, algal growth, biomolecules generated, and recycling the produced biomass for biochar production has been rarely reported. Hence, Chlorella vulgaris was cultivated in DXN-free wastewater (WW1) and 100 mg L -1 DXN-laden wastewater (WW2) in 1-liter photobioreactors with an operating volume of 800 ml under controlled conditions: temperature (25 ± 1 °C), light intensity (351 μmol m -2 s -1 ), and photoperiod (12 h light:12 h dark). Interestingly, this microalgal-based system achieved up to 32.79% removal efficiency of DXN in WW2. In addition, there was no significant difference in the removal of COD (90.6% and 86.8%) and NH 4 -N (74.5% and 76.8%) between WW1 and WW2, respectively. Moreover, the variation in C. vulgaris growth, pigments, lipid, and carbohydrate contents between the two applied wastewaters was negligible. However, there was a significant increase in the protein yield upon exposure to DXN, suggesting the ability of C. vulgaris to secrete various antioxidant and degrading enzymes to detoxify the contaminant. These results were validated by FTIR, SEM, and EDX analysis of C. vulgaris biomass with and without DXN exposure. The harvested biomass was thermally treated at 350 °C for 60 min in an oxygen-free environment. The biochars generated from both algal systems were characterized by comparable morphologies and elemental profiles with sufficient C and N contents, indicating their applicability to enhance the soil properties. The economic evaluation of the combined phycoremediation/pyrolysis system demonstrated a net profit of 596 USD⋅y -1 with a payback period of 6.2 years and fulfilled the objectives of several sustainable development goals (SDGs). This is the first study to point to C. vulgaris as a robust microalgal strain in remediating DXN-laden wastewater accompanied by the potential recyclability of the biomass produced for biochar production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The environmental problems associated with the use of fossil fuels demand a transition to renewable sources for fuels and energy. A biorefinery approach has often been considered and microalgae as a feedstock has been pampered for its numerous possibilities to produce biofuels. Depending on the species and cultivation conditions, microalgae can produce fats, proteins and sugars. These raw materials can thus be utilized in the production of biofuels, bioenergy and biochemicals. For this reason, algal biofuels are considered as sustainable and renewable options for climate related challenges. However, there are many issues such as supply infrastructure, business and refinery opportunities, as well as their efficacy, tied to sustainable production of these energetic materials from algae. Thus, technical maturity, scalability, energy and material balance demands coupled with cost, nutrient resources demand, certification and legislation are needed to demonstrate the biorefinery opportunities of algal biomass valorisation. This paper therefore recommends that various consortiums tasked with algal biofuel projects should be chosen for a more holistic integrated multidisciplinary approach to address the advancement of algal biofuel technology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microalgae are microorganisms that are rich in bioactive compounds, including pigments, proteins, lipids, and polysaccharides. These compounds can be utilized for a number of biomedical purposes, including drug delivery, wound healing, and tissue engineering. Nevertheless, encapsulating microalgae cells and microalgae bioactive metabolites is vital to protect them and prevent premature degradation. This also enables the development of intelligent controlled release strategies for the bioactive compounds. This review outlines the most employed encapsulation techniques for microalgae, with a particular focus on their biomedical applications. These include ionic gelation, oil-in-water emulsions, and spray drying. Such techniques have been widely explored, due to their ability to protect sensitive compounds from degradation, enhance their stability, extend their shelf life, mask undesirable tastes or odours, control the release of bioactive compounds, and enable targeted delivery to specific sites within the body or environment. Moreover, a patent landscape analysis is also provided, allowing an overview of the microalgae encapsulation technology development applied to a variety of fields, including pharmaceuticals, cosmetics, food, and agriculture., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Microalgae as a promising approach for wastewater treatment, has challenges in directly treating digested piggery wastewater (DPW) with high ammonia nitrogen (NH 4 + -N) concentration. To improve the performance of microalgae in DPW treatment, straw was employed as a substrate to form a straw-microalgae biofilm. The results demonstrated that the straw-microalgae biofilm achieved the highest NH 4 + -N removal rate of 193.2 mg L -1  d -1 , which was 28.8 % higher than that of culture system without straw. The final NH 4 + -N concentration in the effluent met the discharge standard of 5 mg L -1 . Furthermore, the total organic carbon (TOC) released from straw facilitated bacterial proliferation and the secretion of extracellular polymeric substances (EPS). The EPS and TOC increased the suspension viscosity and surface tension, thereby enhancing the residence time of CO 2 in the liquid phase and promoting CO 2 fixation. This study presented a novel method for the biological treatment of high-ammonia-nitrogen DPW., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Production of functional biocompounds from microalgae has garnered interest from different industrial sectors; however, their overall productivity must be substantially improved for commercialization. Herein, long-term acclimation of Scenedesmus deserticola was conducted using glucose as an organic carbon source to enhance its heterotrophic capabilities and the production potential of loliolide. A year-long acclimation on agar plates led to the selection of S. deserticola HS4, which exhibited at least 2-fold increase in loliolide production potential; S. deserticola HS4 was subjected to further screening of its cultivation conditions and fed-batch cultivation was subsequently performed in liter-scale reactors. While S. deserticola HS4 exhibited shifts in cellular morphology and biochemical composition, the results suggested a substantial increase in its loliolide productivity regardless of trophic modes. Collectively, these results highlight the potential of long-term acclimation as an effective strategy for improving microalgal crops to align with industrial production practices., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Microalgae-based glycolate production through the photorespiratory pathway is considered an environmentally friendly approach. However, the potential for glycolate production is limited by photoautotrophic cultivation with low cell density and existing strains. In this study, a targeted knockout approach was used to disrupt the key photorespiration enzyme, Chlamydomonas reinhardtii hydroxypyruvate reductase 1 (CrHPR1), leading to a significant increase in glycolate production of 280.1 mg/L/OD 750 . The highest potency yield reached 2.1 g/L under optimized mixotrophic conditions, demonstrating the possibility of synchronizing cell growth with glycolate biosynthesis in microalgae. Furthermore, the hypothesis that the cell wall-deficient mutant facilitates glycolate excretion was proposed and validated by comparing the glycolate accumulation trends of various Chlamydomonas reinhardtii strains. This study will facilitate the development of microalgae-based biotechnology and shed lights on the continuous advancement of green biomanufacturing for industrial application., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The study aimed to evaluate the cyanobacteria Spirulina platensis CMB-02 (S. platensis CMB-02) with self-flocculation properties to treat the ammonia nitrogen of rare earth elements (REEs) wastewater. The results demonstrated that S. platensis CMB-02 could effectively remove total ammonia nitrogen (TAN) and total inorganic nitrogen within 5 days. Simultaneously, a self-flocculation efficiency of 82.59 % was achieved by microalga in 30 min after wastewater treatment. The pH, tightly bound extracellular polymeric substances (TB-EPS), and cell morphology of S. platensis CMB-02 were identified as key factors influencing its self-flocculation capabilities. Moreover, the established semi-continuous process with a 20 % renewal rate showed a stable treatment effect, representing a TAN degradation rate of 10.9 mg/(L·d). These obtained findings could conclude that the developed approach mediated with self-flocculating S. platensis CMB-02 was a promising way for REEs wastewater treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Ultrasound-assisted extraction (UAE) shows great potential in exploiting microalgal compounds. However, upgrading the extraction system lacks concerns. This study proposes a novel sono-reactor featuring a microbubble distributor for increasing bubble abundance and correspondingly improving microalgal compound extraction. Results indicate that protein concentrations increase with ultrasound powers and extraction time while an optimized gas flow rate exists. The optimal parameters by Box-Behnken design are power 646.0 W, nitrogen flow rate 25.0 mL/min, and time 40.0 min, with an optimal protein concentration of 249.1 mg/L - a substantial improvement over gas-free extraction. The strategic increase in bubble abundance enhances microalgal compound extraction efficiency and extraction kinetics. The system innovation will contribute to the advancement of bioresource utilization and sustainability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Monoclonal antibodies (mAbs) have become indispensable tools in various fields, from research to therapeutics, diagnostics, and industries. However, their production, primarily in mammalian cell culture systems, is cost-intensive and resource-demanding. Microalgae, diverse photosynthetic microorganisms, are gaining attention as a favorable option for manufacturing mAbs and various other recombinant proteins. This review explores the potential of microalgae as a robust expression system for biomanufacturing high-value proteins. It also highlights the diversity of microalgae species suitable for recombinant protein. Nuclear and chloroplast genomes of some microalgae have been engineered to express mAbs and other valuable proteins. Codon optimization, vector construction, and other genetic engineering techniques have significantly improved recombinant protein expression in microalgae. These accomplishments demonstrate the potential of microalgae for biopharmaceutical manufacturing. Microalgal biotechnology holds promise for revolutionizing the production of mAbs and other therapeutic proteins, offering a sustainable and cost-effective solution to address critical healthcare needs., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Microalgal-bacterial granular sludge (MBGS) could offer a sustainable alternative to traditional aerobic methods in brewery wastewater (BWW) treatment. This study compared MBGS with conventional activated sludge (AS) in treating real BWW and highlighted its advantages and challenges. MBGS achieved comparable chemical oxygen demand removal efficiency (93%) compared to AS (89%). Additionally, MBGS exhibited higher phosphate removal capabilities than AS. Extra nitrogen was added to influent to balance C/N ratio of BWW. MBGS was robust in handling C/N ratio fluctuations with an 82% total nitrogen removal efficiency. Metagenomic analysis further indicated that most of the genes involved in carbon, nitrogen and phosphorus metabolism were up-regulated in MBGS compared to AS. Despite changes in the microbial community and settling ability due to high starch and sugar content in BWW, MBGS demonstrated high efficiency and sustainability. Further research should optimize MBGS operation strategies to fully realize its potential for sustainable BWW treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Extracellular soluble algal organic matter (AOM) significantly interferes with microalgae flocculation. This study investigated the effects of various AOM fractions on Chlorella sp. flocculation using ferric chloride (FeCl 3 ), sodium hydroxide (NaOH), and chitosan. All flocculants achieved high separation efficiency (87-99 %), but higher dosages were required in the presence of AOM. High molecular weight (>50 kDa) AOM fraction was identified as the primary inhibitor of flocculation across different pH levels, whereas low/medium molecular weight (<3 and <50 kDa) AOM had minimal impact. Compositional analysis revealed that the inhibitory AOM fraction is a glycoprotein rich in carbohydrates, including neutral, amino, and acidic sugars. The significance of this study is in identifying carboxyl groups (-COOH) from acidic monomers in >50 kDa AOM that inhibit flocculation. Understanding AOM composition and the interaction dynamics between AOM, cells, and flocculants is crucial for enhancing the techno-economics and sustainability of flocculation-based microalgae harvesting., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microalgae have long been regarded as a promising solution for biological carbon abatement from the power industry, offering renewable biomass without competing for land or water resources used for food crops. In this study, we extensively examined the application of photosynthetic microorganisms for closing carbon, nitrogen, and micronutrient loops in the power industry. Subsequently, we explored the bottom-up integration of algal biorefineries into power industry waste streams for increased economic benefits and reduced environmental impacts. Analysis of the available data indicated that microalgae integration with the power industry is primarily performed using flue-gas-assisted cultivation. This approach allows for carbon sequestration typically below one gram per liter per day, too low to significantly impact carbon abatement at achievable scales of microalgae cultivation. Alternative approaches are also being explored. For example, soluble bicarbonate platforms allow for higher biomass productivity and temporary carbon storage. Meanwhile, the use of ashes and waste heat and thermophilic strains can result in lower cultivation costs and better control of cultivation conditions. These approaches offer further incremental improvement to microalgae-based carbon abatement systems in the power industry but are unlikely to be an umbrella solution for carbon reduction. Consequently, in the near term, microalgae-based carbon valorization systems are likely to be limited to niche applications involving the synthesis of high-value products. For microalgae to truly transform carbon abatement processes radical improvements in both biology and engineering approaches are urgently needed.

Microalgae-based biotechnology is one of the most promising alternatives to conventional methods for the removal of antibiotic contaminants from diverse water matrices. However, current knowledge regarding the biochemical mechanisms and catabolic enzymes involved in microalgal biodegradation of antibiotics is scant, which limits the development of enhancement strategies to increase their engineering feasibility. In this study, we investigated the removal dynamics of amphenicols (chloramphenicol, thiamphenicol, and florfenicol), which are widely used in aquaculture, by Chlamydomonas reinhardtii under different growth modes (autotrophy, heterotrophy, and mixotrophy). We found C. reinhardtii removed >92 % chloramphenicol (CLP) in mixotrophic conditions. Intriguingly, gamma-glutamyl hydrolase (GGH) in C. reinhardtii was most significantly upregulated according to the comparative proteomics, and we demonstrated that GGH can directly bind to CLP at the Pro77 site to induce acetylation of the hydroxyl group at C3 position, which generated CLP 3-acetate. This identified role of microalgal GGH is mechanistically distinct from that of animal counterparts. Our results provide a valuable enzyme toolbox for biocatalysis and reveal a new enzymatic function of microalgal GGH. As proof of concept, we also analyzed the occurrence of these three amphenicols and their degradation intermediate worldwide, which showed a frequent distribution of the investigated chemicals at a global scale. This study describes a novel catalytic enzyme to improve the engineering feasibility of microalgae-based biotechnologies. It also raises issues regarding the different microalgal enzymatic transformations of emerging contaminants because these enzymes might function differently from their counterparts in animals., Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest in this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microalgae are considered promising sustainable sources of natural bioactive compounds to be used in biotechnological sectors. In recent years, attention is increasingly given to the search of microalgae-derived compounds with antioxidant and anti-inflammatory properties for nutraceutical or pharmacological issues. In this context, attention is usually focused on the composition and bioactivity of algae or their extracts, while less interest is driven to their biological features, for example, those related to morphology and cultivation conditions. In addition, specific studies on the antioxidant and anti-inflammatory properties of microalgae mainly concern Chlorella or Spirulina. The present work was focused on the characterization of the Chlorophyta Neochloris oleoabundans under two combinations of cultivation modes: autotrophy and glucose-induced mixotrophy, each followed by starvation. Biomass for morphological and biochemical characterization, as well as for extract preparation, was harvested at the end of each cultivation phase. Analyses indicated a different content of the most important classes of bioactive compounds with antioxidant/anti-inflammatory properties (lipids, exo-polysaccharides, pigments, total phenolics, and proteins). In particular, the most promising condition able to prompt the production of antioxidant algal biomass with anti-inflammatory properties was the mixotrophic one. Under mixotrophy, beside an elevated algal biomass production, a strong photosynthetic metabolism with high appression of thylakoid membranes and characteristics of high photo-protection from oxidative damage was observed and linked to the overproduction of exo-polysaccharides and lipids rather than pigments. Overall, mixotrophy appears a good choice to produce natural bioactive extracts, potentially well tolerated by human metabolism and environmentally sustainable., (© 2024. The Author(s).)

Algae-derived protein has immense potential to provide high-quality protein foods for the expanding human population. To meet its potential, a broad range of scientific tools are required to identify optimal algal strains from the hundreds of thousands available and identify ideal growing conditions for strains that produce high-quality protein with functional benefits. A research pipeline that includes proteomics can provide a deeper interpretation of microalgal composition and biochemistry in the pursuit of these goals. To date, proteomic investigations have largely focused on pathways that involve lipid production in selected microalgae species. Herein, we report the current state of microalgal proteome measurement and discuss promising approaches for the development of protein-containing food products derived from algae.

Since microalgae face various environmental stresses for the high production of biofuels, multiple studies have been performed to determine if microalgae are resistant to these various stresses. In this study, the viability of cells under various abiotic stresses was investigated by introducing a putative germin-like protein (GLP) from Neopyropia yezoensis , which was known to be related in the resistance to abiotic stresses. The expression of GLP in Chlamydomonas reinhardtii allowed cells to grow better in various abiotic stress environments. In nitrogen starvation conditions, recombinant cells accumulated the lipid droplet 1.46-fold more than wild-type cells and responded more rapidly to form palmelloid forms. Under high-temperature, hydrogen peroxide conditions and saline stress, the survival rate was increased 3.5 times, 2.19 times, and 3.19 times in recombinant C. reinhardtii with GLP, respectively. The expression level of genes related to pathways in response to various stresses increased 2-fold more under those conditions. This result will be useful for the development of microalgae that can grow better and produce more biofuels under different stress conditions.

In recent years, reducing the concentration of carbon dioxide in the atmosphere has become an important issue. Microalgae have a higher photosynthetic efficiency and growth rate than higher plants; thus, biological carbon dioxide fixation using microalgae is attracting particular attention as an efficient carbon dioxide fixation method. However, under dilute atmospheric conditions, microalgae exhibit lower growth rates and reduced carbon dioxide fixation efficiency. In recent years, technology that can efficiently fix carbon dioxide, even in the atmosphere, using a microalgae co-culture system that co-cultivates microalgae and heterotrophic microorganisms has attracted attention. In such a co-culture system, it is believed that a mutualistic relationship is established between microorganisms through the exchange of various compounds. This review focuses on the application of a co-culture system of microalgae and heterotrophic microorganisms for bioproduction and wastewater treatment. In addition, research to elucidate the mutualistic relationships in microalgal co-culture systems using analytical methods that have been widely used in recent years, such as next-generation sequencing technology, is also discussed. In the future, it is expected that the use of microalgae co-culture systems will expand on an industrial scale through the development of key technologies, such as efficient genetic modification techniques for microalgae and their heterotrophic microorganism partners, large-scale cultivation facilities that can efficiently cultivate microalgae, and stable control techniques for co-culture systems using advanced technology., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Microalgae contain two main groups of pigments: chlorophylls and carotenoids. Chlorophyll is a green pigment that absorbs light energy and transforms it into chemical energy to facilitate the synthesis of organic compounds. This pigment serves as a valuable primary source for biotechnological input products in the food, pharmaceutical, and cosmetic industries due to its high antioxidant properties and coloring capabilities. The objective of this research was to evaluate the effect of growth factors (CO2 concentration, light color, and light intensity) through a Taguchi L4 experimental design on cell growth and the cellular content of chlorophyll a and b in Chlorella sorokiniana, followed by validation of the method using Haematococcus pluvialis microalgae as an additional study model. Cell growth was quantified using the optical density spectrophotometric technique at a wavelength of 550 nm. For the quantification of chlorophylls, a cell extract was obtained using a 90% pure acetone solution, and subsequently, the concentrations of chlorophylls a and b were quantified using spectrophotometric techniques at wavelengths of 647 nm and 664 nm, according to the method described by Jeffrey and Humphrey. The experimental results indicated that controlling conditions of low CO2 addition, purple light, and low light intensity increases both cell growth and the concentration of chlorophylls a and b within the cells. The implementation of this chlorophyll quantification method allows for quick, simple, and precise determination of chlorophyll content, as the wavelengths used are at the absorbance peaks of both types of chlorophylls, making this technique easily reproducible for any microalgae under study.

Background: Microalgae are potential sustainable resources for the production of value-added chemicals that can be used as biofuels, pharmaceuticals, and nutritional supplements. Arachidonic acid (ARA), a omega-6 fatty acid, plays a crucial role in infant development and immune response, and can be used in cosmetics and pharmaceuticals. Demand for industrial-scale ARA production is continuously increasing because of its broad applicability. To address this demand, there has been a significant shift towards microorganism-based ARA production. To accelerate large-scale ARA production, it is crucial to select suitable strains and establish optimal culture conditions., Results: Here, we isolated a novel microalga Lobosphaera incisa CFRC-1, a valuable strain that holds promise as a feedstock for ARA production. Optimal cultivation conditions were investigated using a high-throughput screening method to enhance ARA production in this novel strain. Out of 71 candidates, four organic carbon substrates were identified that could be utilized by L. incisa CFRC-1. Through flask-scale verification, fructose was confirmed as the optimal organic carbon substrate for promoting microalgal growth, total lipid accumulation, and ARA production. Subsequently, we investigated appropriate substrate concentration and cultivation temperature, confirming that the optimal conditions were 30 g L - 1 of fructose and 27 ℃ of temperature. Under these optimized conditions, biomass and ARA production reached 13.05 ± 0.40 g L - 1 and 97.98 ± 7.33 mg L - 1 , respectively, representing 9.6-fold and 5.3-fold increases compared to the conditions before optimization conditions. These results achieved the highest biomass and ARA production in flask-scale cultivation, indicating that our approach effectively improved both production titer and productivity., Conclusions: This study presents a novel microalgae and optimized conditions for enhancing biomass and ARA production, suggesting that this approach is a practical way to accelerate the production of valuable microalgae-based chemicals. These findings provide a basis for large-scale production of ARA-utilizing microalgae for industrial applications., (© 2024. The Author(s).)

The phenolic antioxidant 2,6-Di-tert-butyl-p-cresol (BHT) has been detected in various environments and is considered a potential threat to aquatic organisms. Algal-bacterial interactions are crucial for maintaining ecosystem balance and elemental cycling, but their response to BHT remains to be investigated. This study analyzed the physiological and biochemical responses of the microalga Isochrysis galbana and the changes of associated bacterial communities under different concentrations of BHT stress. Results showed that the biomass of I. galbana exhibited a decreasing trend with increasing BHT concentrations up to 40 mg/L. The reduction in chlorophyll, carotenoid, and soluble protein content of microalgal cells was also observed under BHT stress. The production of malondialdehyde and the activities of superoxide dismutase, peroxidase, and catalase were further determined. Scanning electron microscopy analysis revealed that BHT caused surface rupture of the algal cells and loss of intracellular nutrients. Proteomic analysis demonstrated the upregulation of photosynthesis and citric acid cycle pathways as a response to BHT stress. Additionally, BHT significantly increased the relative abundance of specific bacteria in the phycosphere, including Marivita, Halomonas, Marinobacter, and Alteromonas. Further experiments confirmed that these bacteria had the ability to utilize BHT as the sole carbon resource for growth, and genes related to the degradation of phenolic compounds were detected through pangenome analysis., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

DpAP2 is a transcription factor regulating carotenoid biosynthesis pathway. It was speculated that MeJA significantly decreased expression of DpAP2 gene, then the decreasing DpAP2 expression significantly inhibited expression of some key enzyme genes such as PSY, PDS and GGPS in carotenoid biosynthesis pathway. In contrast, it was speculated that GA3 significantly increased expression of DpAP2 gene, then the increasing DpAP2 expression significantly increased expression of some key enzyme genes such as PDS and GGPS in carotenoid biosynthesis pathway. To increase the content of carotenoid, we evaluated the effect of DpAP2 overexpression on carotenoid accumulation in D. parva. Transgenic D. parva showed a higher carotenoid content (3.18 mg/g DW) compared with control group (2.13 mg/g DW) at 9 d. The dosage effects of exogenous hormones MeJA and GA3 were found in D. parva cells treated with different concentrations of MeJA (10, 20, 50, 100 μM) and GA3 (10, 20, 50, 100 μM). The high concentrations of MeJA (10-100 μM) inhibited the accumulation of carotenoid, and the relative expression of DpAP2, PSY, PDS and GGPS decreased significantly. On the contrary, the relative expression of DpAP2, PDS and GGPS increased significantly when D. parva was treated with 10, 20, 50 and 100 μM GA3, which promoted the biosynthesis of carotenoid. Therefore, we inferred that there was a hierarchical regulation from hormone, transcription factor, key enzyme gene to carotenoid accumulation in carotenoid biosynthesis. Carotenoid biosynthesis was enhanced by DpAP2 overexpression (1.4930 fold of control) and exogenous substances such as GA3 (1.5889 fold of control), which laid a foundation for massive accumulation of carotenoids in microalgae. In the future, further studies were required to demonstrate the complex regulatory network., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Ruan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

This study explores the potential of strain selection and adaptation for developing a fungi-yeast-microalgae consortium capable of integrated bioethanol production and livestock wastewater treatment. We employed a multi-stage approach involving isolation and strain selection/adaptation of these consortiums. The study started with screening some isolated fungi to grow on the cellulosic biomass of the livestock wastewater (saccharification) followed by a fermentation process using yeast for bioethanol production. The results revealed that Penicillium chrysogenum (Cla) and Saccharomyces cerevisiae (Sc) produced a remarkable 99.32 ppm of bioethanol and a concentration of glucose measuring 0.56 mg ml - 1 . Following the impact of fungi and yeast, we diluted the livestock wastewater using distilled water and subsequently inoculated Nile River microalgae into the wastewater. The findings demonstrated that Chlorella vulgaris emerged as the dominant species in the microalgal community. Particularly, the growth rate reached its peak at a 5% organic load (0.105385), indicating that this concentration provided the most favorable conditions for the flourishing of microalgae. The results demonstrated the effectiveness of the microalgal treatment in removing the remaining nutrients and organic load, achieving a 92.5% reduction in ammonia, a 94.1% reduction in nitrate, and complete removal of phosphate (100%). The algal treatment also showed remarkable reductions in COD (96.5%) and BOD (96.1%). These findings underscore the potential of fungi, yeast, and Nile River microalgae in the growth and impact on livestock wastewater, with the additional benefit of bioethanol production., (© 2024. The Author(s).)

This study investigated the effects of gamma ( 137 Cs, 0-250 Gy) and UV (UV-C, 0-12 h) radiation on growth and biodiesel properties of Botryococcus braunii KMITL. For gamma radiation, maximum biomass (1.37 ± 0.02 g L -1 ) was achieved with 50 Gy, while a dose of 200 Gy resulted in the highest hydrocarbon content (51.84 ± 0.20%) and yield (0.66 ± 0.01 g L -1 ). For UV radiation, a 9 h exposure produced the highest biomass (2.45 ± 0.05 g L -1 ), hydrocarbon content (55.01 ± 1.22%), and yield (1.35 ± 0.04 g L -1 ). Algae exposed to gamma radiation within the range of 0-150 Gy exhibited C16:0 as the dominant fatty acid methyl ester (FAME), similar to those exposed to UV radiation, while algae exposed to 200-250 Gy displayed C18:1n9t as the dominant FAME. High levels of gamma and UV radiation were observed to lengthen fatty acid chains and increase unsaturated fatty acids. The cetane values of biodiesel from algae exposed to gamma and UV radiation ranged from 64.55 ± 0.14-66.47 ± 0.20 and 59.43 ± 0.04-65.27 ± 0.22, respectively, all meeting standard criteria. Both gamma and UV radiation also improved the saponification value and cold flow properties of the biodiesel. These findings suggest that controlled levels of gamma and UV radiation effectively enhance hydrocarbon yields with significant implications for biofuel production., (© 2024. The Author(s).)

Wastewater generated by the pork industry urgently requires the implementation of low-cost, high-benefit, and efficient treatment systems. Accordingly, a microalgae-bacteria consortia-based treatment system is proposed for the removal of contaminants released, by the pork-producing industry, in swine wastewater. In this study, different inoculum concentrations of the microalgae-bacteria consortium were tested to document variation in the removal of nutrients from the wastewater. At varying concentrations, it was efficient and did not present a significant difference in the removal kinetics. The treatment with the greatest amount of inoculum removed close to 87% of total nitrogen, approximately 70% of orthophosphate, and 77% of chemical oxygen demand. Removals of 84% iron, 44% copper, and 48% manganese were also obtained. These results demonstrate that microalgae-bacteria consortia are an economically viable and environmentally desirable option for the efficient treatment of wastewater from the pork industry., (© 2024. The Author(s).)

Microalgae are significantly influenced by light quality and quantity, whether in their natural habitats or under laboratory and industrial culture conditions. The present study examines the adaptive responses of the marine microalga Tetraselmis chuii to different light regimes, using a cost-effective filtering method and a multi-omics approach. Microalgal growth rates were negatively affected by all filtered light regimes. After six days of cultivation, growth rate for cultures exposed to blue and green filtered light was 67%, while for red filter was 83%, compared to control cultures. Transcriptomic analysis revealed that the usage of green filters resulted in upregulation of transcripts involved in ribosome biogenesis or coding for elongation factors, exemplified by a 2.3-fold increase of TEF3. On the other hand, a 2.7-fold downregulation was observed in photosynthesis-related petJ. Exposure to blue filtered light led to the upregulation of transcripts associated with pyruvate metabolism, while photosynthesis was negatively impacted. In contrast, application of red filter induced minor transcriptomic alterations. Regarding metabolomic analysis, sugars, amino acids, and organic acids exhibited significant changes under different light regimes. For instance, under blue filtered light sucrose accumulated over 6-fold, while aspartic acid content decreased by 4.3-fold. Lipidomics analysis showed significant accumulation of heptadecanoic and linoleic acids under green and red light filters. Together, our findings indicate that filter light can be used for targeted metabolic manipulation., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Aerobic metabolism relies on external oxygen production through photosynthesis and its subsequent transport into each cell of the body via the cardiorespiratory system. This mechanism has successfully evolved over millions of years, enabling animals to inhabit most environments on Earth. However, the insufficient oxygen supply leads to several clinical problems, ranging from non-healing wounds to tumor resistance to therapy. Given that photosynthetic microorganisms are capable of producing oxygen and removing carbon dioxide from the environment, over the last decade, several groups worldwide have proposed their potential use as an alternative tissue oxygenation approach. While most studies have demonstrated safety and efficacy after local tissue administration, recent studies have also suggested that systemic administration could trigger intravascular photosynthesis. If successful, the development of a new generation of circulating cells, known as chlorocytes, may partially replace the role of erythrocytes in gas exchange within the body, without relying on external supply and vascular flow. This work reviews the existing literature on local and systemic administration of photosynthetic microorganisms, highlighting the main challenges in the field and potential solutions to unleash the enormous potential clinical impact of chlorocytes and intravascular photosynthesis. KEY POINTS: • Circulating photosynthetic microorganisms could deliver oxygen to tissues • Microalgae and cyanobacteria have shown safety and efficacy for oxygen delivery • Several key challenges need to be addressed for the clinical success of chlorocytes., (© 2024. The Author(s).)

Microalgae are emerging as a promising feedstock for bioplastics, with Chlorella vulgaris yielding significant amounts of starch. This polysaccharide is convertible into thermoplastic starch (TPS), a biodegradable plastic of industrial relevance. In this study, we developed a pilot-scale protocol for extracting and purifying starch from 430 g (dry weight - DW) of starch-enriched Chlorella vulgaris biomass. More than 200 g DW of starch were recovered, with an extraction yield and starch purity degree reaching 98 and 87 %, respectively. We have characterized this extracted starch and processed it into TPS using twin-screw extrusion and injection molding. Microalgal starch showed similar properties to those of native plant starch, but with smaller granules. We compared the mechanical properties of microalgal TPS with two controls, namely a commercial TPS and a TPS prepared from commercial potato starch granules. TPS prepared from microalgal starch showed a softer and more ductile behavior compared to the reference materials. This study demonstrates the feasibility of recovering high-purity microalgal starch at pilot scale with high yields, and highlights the potential of microalgal starch for the production of TPS using industrially relevant processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Increasing amounts of wastewater is the most pervasive and challenging environmental problem globally. Conventional treatment methods are costly and entail huge energy, carbon consumption and greenhouse gas emissions. Owing to their unique ability of carbon capturing and resource recovery, microalgae-microbiome based treatment is a potential approach and is widely used for carbon-neutral wastewater treatment. Microalgae-bacteria synergy (i.e., the functionally beneficial microbial synthetic communities) performs better and enhances carbon-sequestration and nutrient recovery from wastewater treatment plants. This review presents a comprehensive information regarding the potential of microalgae-microbiome as a sustainable agent for wastewater and discusses synergistic approaches for effective nutrient removal. Moreover, this review discusses, the role of omics-biology and Insilco approaches in unravelling and understanding the algae-microbe synergism and their response toward wastewater treatment. Finally, it discusses various microbiome engineering approaches for developing the effective microalgae-bacteria partners for carbon sequestration and nutrient recovery from wastewater, and summarizes future research perspectives on microalgae-microbiome based bioremediation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Cultivation of microalgae using anaerobic digestate is a gain-win strategy for algal biomass production and achieving environmental benefits. However, the low biomass concentration and high harvest cost of the conventional suspended microalgae culture system are troublesome issues. In this study, a novel fluidized bed photobioreactor (FBPBR) based on diatomite powder was constructed for cultivating Scenedesmus quadricauda and treating diluted anaerobic digestate. The optimized diatomite carrier dosage of 750 mg/L increased microalgal biomass concentration to 1.58 g/L compared to suspended microalgae without carrier (0.99 g/L). When the light intensity was increased from 100 to 200 μmol/m 2 /s, the microalgal biomass in the FBPBR increased to 1.84 g/L and the settling efficiency increased to 93.58 %. This was due to the 1.60-fold enhancement of extracellular polymeric substance (EPS) secretion and changes in EPS properties. The increase in hydrophobic functional groups of EPS under high light intensity, coupled with the reconstitution of protein secondary structure, facilitated the initial attachment of algae to diatomite and the thickening of microalgal biofilm. Moreover, transcriptomic analysis demonstrated that diatomite promoted antioxidant defense and photosynthesis in S. quadricauda cells, alleviating the adverse effect of anaerobic digestate stress. The diatomite addition and elevated light intensity contributed to the highest lipid content (60.37 %), which was owing to the upregulated genes encoding fatty acid and triacylglycerol synthesis under the stress of localized nutrient starvation in the inner layer of microalgae biofilms. Furthermore, the regulation of phosphorus metabolism and NH 4 + -N assimilation improved nutrient removal (93.24 % and 96.86 % for NH 4 + -N and TP removal). This work will provide guidance for the development of FBPBR based on diatomite powder., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Microalgae play an important role in aquatic ecosystems, but the widespread presence of micro- and nano-plastics (MNPs) poses significant threats to them. Haematococcus pluvialis is well-known for its ability to produce the antioxidant astaxanthin when it experiences stress from environmental conditions. Here we examined the effects of polystyrene nanoplastics (PS-NPs) at concentrations of 0.1, 1, and 10 mg/L on H. pluvialis over an 18-day period. Our results show that PS-NPs caused a significant, dose-dependent inhibition of H. pluvialis growth and a reduction in photosynthesis. Furthermore, PS-NPs severely damaged the morphology of H. pluvialis, leading to cell shrinkage, collapse, content release, and aggregation. Additionally, PS-NPs induced a dose-dependent increase in soluble protein content and a decrease in the production of extracellular polymeric substances. These findings indicate that PS-NPs has the potential to adversely affect both the physiology and morphology of H. pluvialis. An increase in reactive oxygen species and antioxidant enzyme activities was also observed, suggesting an oxidative stress response to PS-NPs exposure. Notably, the synthesis of astaxanthin, which is crucial for H. pluvialis's survival under stress, was significantly inhibited in a dose-dependent manner under strong light conditions, along with the down-regulation of genes involved in the astaxanthin biosynthesis pathway. This suggests that PS-NPs exposure reduces H. pluvialis's ability to survive under adverse conditions. This study enhances our understanding of the toxic effects of PS-NPs on microalgae and underscores the urgent need for measures to mitigate MNP pollution to protect aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Construct a bacteria-algae symbiotic dynamic sponge bioremediation system to simultaneously remove multiple pollutants under micro-pollution conditions. The average removal efficiencies of NH 4 + -N, PO 4 3- -P, total nitrogen (TN), and Ca 2+ were 98.35, 78.74, 95.64, and 84.92 %, respectively. Comparative studies with Auxenochlorella sp. sponge and bacterial sponge bioremediation system confirmed that NH 4 + -N and TN were mainly removed by bacterial heterotrophic nitrification - aerobic denitrification (HN-AD). PO 4 3- -P was removed by algal assimilation and the generation of Ca 3 (PO 4 ) 2 and Ca 5 (PO 4 ) 3 OH, and Ca 2+ was removed by algal electron transfer formation of precipitates and microbially induced calcium precipitation (MICP) by bacteria. Algae provided an aerobic environment for the bacterial HN-AD process through photosynthesis, while respiration produced CO 2 and adsorbed Ca 2+ to promote the formation of calcium precipitates. Immobilization of Ca 2+ with microalgae via bacterial MICP helped to lift microalgal photoinhibition. The bioremediation system provides theoretical support for research on micropolluted water treatment while increasing phosphorus recovery pathways., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)