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This study investigates the biomass and carbon fixation rate of Chlorella sp. by the main valuable elements in converter steel slag in F/2 seawater medium. The results indicate that Ca, Mg, P, Si, Fe, and Mn can increase the biomass and carbon fixation rate of Chlorella sp., while Cu, Zn, Cr, and Al can decrease the biomass and carbon fixation rate of Chlorella sp.. Three machine learning methods known as Back Propagation neural network (BPNN), decision tree (DT), and random forest (RF) were applied to construct the prediction model for the carbon fixation rate of Chlorella sp. based on real-life experimental data obtained from single factor experiments. The overall results exhibited that the BPNN model is better than the DT model and RF model to predict the carbon fixation rate of Chlorella sp.. Finally, the maximum carbon fixation rate for Chlorella sp. predicted by BPNN model is 50.86 mg/(L·d), which was 2.46 times that of the control group, under the optimum conditions of Ca 5.77 g/L, Mg 4.74 g/L, P 1.27 g/L, Si 6.31×10−1 g/L, Fe 6.50×10−4 g/L, Mn 5.00×10−5 g/L, Cu 2.51×10−6 g/L, Zn 4.98×10−6 g/L, Cr 0 g/L, and Al 0 g/L in F/2 seawater medium.

Background: Ferredoxin 1 (Fd1) is the main electron donor to hydrogenase (HydA) for generating molecular hydrogen (H2) in green microalgae. In order to obtain an increased H2 production, the Fd1 of Chlamydomonas reinhardtii (CrFd1, encoded by crfd1) was therefore overexpressed in Chlorella sp. DT (DT) in this study. Results: The coding region of crfd1 was constructed into the p121-crfd1 plasmid, which was also constructed with a resistance gene to the antibiotic geneticin (G418) as a selection marker. The p121-crfd1 plasmid was transformed into DT cells by electroporation. Observation of the crfd1 gene fragment in the genomic DNA of DT-crfd1 mutants by PCR indicated that the transgene was successfully transformed. Using western blotting, the overexpressed CrFd1 protein, with a molecular weight of about 14 kDa, was found in DT-crfd1 mutants of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23. Using an in vitro assay, the H2 production of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23 mutants was about 4.4-, 5.0-, and 3.8-fold higher, respectively, than the DT wild type (DT-WT). Using an in vivo assay, the H2 production of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23 mutants was about 1.3-, 1.4-, and 1.2-fold higher, respectively, than the DT-WT. Conclusions: The results suggested that heterologous overexpression of CrFd1 could enhance H2 production in DT-crfd1 mutants even though in vitro H2 production of DT-crfd1-22 mutant was up to 5-fold higher than the DT-WT.How to cite: Lin YJ, Chien LF. Hydrogen production in the Chlorella sp. DT mutants carrying heterologous electron donor ferredoxin 1 of Chlamydomonas reinhardtii. Electron J Biotechnol 2024;69. https://doi.org/10.1016/j.ejbt.2024.03.001.

Optimization can streamline experimental trials by evaluating the parameters and parameter interactions used as the basis for a more optimal downstream process. This study aims to optimize the microwave-assisted pyrolysis process in producing bio-oil from microalgae using response surface methodology (RSM) complemented by an investigation of the reaction mechanisms. A number of key parameters (microwave power, absorbent-to-microalgae ratio, and pyrolysis time) were fine-tuned using a face-centered central composite design. The result showed that microwave technology in slow pyrolysis could produce the bio-oil from microalgae 12 times shorter than conventional heating and quadratic model with a high precision (R2 = 0.9832, R2adj = 0.9616) from RSM optimization in predicting experimental values yielded a peak bio-oil yield of 19.11% under specific conditions: 20 min of pyrolysis time, a 0.19 (w/w) microwave absorber to microalgae ratio, and 583 W power. As the complex biomass, the reaction mechanism in chlorella sp. towards this technology including decarboxylation, decarbonylation, dehydration, cracking, deoxygenation, and esterification was proved in GCMS analysis, revealing the presence of key functional groups such as aliphatic, aromatics, alcohols, nitrogenous compounds, fatty acid methyl esters (FAME) and Polycyclic Aromatics Hydrocarbons (PAHs).

This paper presents the data on growth performance of marine Chlorella sp. cultured in different cost-effective media including cow dung, cow urine, poultry litter, compost, NPK (nitrogen, phosphorus, and potassium), and UTR (Urea, TSP, and red potash). Growth curve of Chlorella sp. was determined at 5 mg of cow dung, poultry litter, compost, NPK, UTR and 5 µL of cow urine per 350 ml sea water (25 ppt) to identify the onset of stationary phase. Further four media among these were selected to continue the experiment at 8 mg and 11 mg of concentration. The higher cell densities were 4.21 × 106 and 4.18 × 106 cells/mL for NPK at 8 mg and 11 mg of concentration on 6th and 5th day, respectively. Cow dung with an 11 mg of concentration exhibited 2.67 × 106 cells/mL on the 3rd day, which is around 1.5 times greater than the highest growth in the same concentration of poultry litter. Chlorella sp. had a higher cell density in NPK media than in other media, however it was discarded since it is inorganic and costly. Due to the low cell density in cow urine media and the prolonged stationary phase in poultry litter media, the focus of the subsequent study was then placed on cow dung media. The data will contribute to the selection of locally available and cost-effective culture media by determining the stationary phases for specific microalgal species which will replace the costly and labor-intensive commercial media.

Chronic diabetic wound remains a critical challenge suffering from the complicated negative microenvironments, such as high-glucose, excessive reactive oxygen species (ROS), hypoxia and malnutrition. Unfortunately, few strategies have been developed to ameliorate the multiple microenvironments simultaneously. In this study, Chlorella sp. (Chlorella) hydrogels were prepared against diabetic wounds. In vitro experiments demonstrated that living Chlorella could produce dissolved oxygen by photosynthesis, actively consume glucose and deplete ROS with the inherent antioxidants, during the daytime. At night, Chlorella was inactivated in situ by chlorine dioxide with human-body harmless concentration to utilize its abundant contents. It was verified in vitro that the inactivated-Chlorella could supply nutrition, relieve inflammation and terminate the oxygen-consumption of Chlorella-respiration. The advantages of living Chlorella and its contents were integrated ingeniously. The abovementioned functions were proven to accelerate cell proliferation, migration and angiogenesis in vitro. Then, streptozotocin-induced diabetic mice were employed for further validation. The in vivo outcomes confirmed that Chlorella could ameliorate the undesirable microenvironments, including hypoxia, high-glucose, excessive-ROS and chronic inflammation, thereby synergistically promoting tissue regeneration. Given the results above, Chlorella is considered as a tailor-made therapeutic strategy for diabetic wound healing.

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.)

Lately, the bio electrochemical systems are emerging as an efficient wastewater treatment and energy conversion technology. However, their scaling-up is considerably restrained by slow-rate of cathodic oxygen reduction reaction (ORR) or otherwise by the high cost associated with the available efficient ORR catalysts. In this investigation, a cost-effective and eco-friendly approach for synthesizing Ni based ORR catalyst utilizing biosorption property of microalgae is accomplished. The synthesised Ni adsorbed algal biochar (NAB) served as an efficient cathode catalyst for enhancing ORR in a microbial carbon-capture cell (MCC). On increasing the initial concentration of Ni 2+ in the aqueous medium from 100 mgL -1 to 500 mgL -1 , the biosorption capacity was found to increase from 3 mgg -1 to 32 mgg -1 of algae cell. The MCC operated with NAB based cathode catalyst loading of 2 mgcm- 2 exhibited 3.5 times higher power density (4.69 Wm -3 ) as compared to the one with commercial activated carbon. A significant organic matter removal (82 %) in the anodic chamber with simultaneous algal biomass productivity in the cathodic chamber was attained by MCC with cathode loaded with 2 mgcm -2 of NAB. Hence, this easily synthesised low-cost catalyst, out of waste stream, proved its ability to improve the performance of MCC., 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.)

Dhiba port has a strategic location near the Neom project. Various anthropogenic activities contributed to the discharge of metals, metalloids and oil spills in the aquatic system and caused environmental pollution. Microalgae are the best microorganisms in aquatic conditions known to be capable of eliminating contaminants. In this work the Chlorella sp. was isolated from seawater, the metals, metalloids were determine using ICP- OES (Inductively Coupled Plasma-Optical Emission Spectrometer) and hydrocarbons were determine using GC-MS in different five sites in Dhiba port, after and before treated with Chlorella sp, and immobilized Chlorella sp. The growth parameters (optical density and pigment contents) of Chlorella sp and immobilized Chlorella sp. were investigated during 14 days of grown. The results showed that the most contaminated site by metals and metalloids was site no 3, by Sb, As, Be, Se, and Zn with concentrations 0.07546, 0.05709, 0.09326, 0.4618, and 0.00979 mg/L respectively, and site no 1 was the most contamination by organic compounds, so the site no 1 and site no 3 were chosen to test the efficiency of Chlorella sp. and immobilized Chlorella sp. to remove hydrocarbons and both metals and metalloids. Chlorella sp. and immobilized Chlorella sp. had completely removed metals and metalloids that were present in site 3. There were only 6 compounds remained, after treatments with immobilized alga in site 1. Immobilized Chlorella sp. is the most effective than suspended Chlorella sp in reduces the number of organic compounds in contaminated area. It is an economic tool due to simplifying harvesting and then retaining for further processing.

The present work evaluates the bioremediation potential of the microalgae Chlorella sp. cultivated in industrial wastewaters of a metallurgy facility for CO2 fixation. Its growth in wastewaters was investigated experimentally and growth rate was determined based on different dilutions. Taguchi's experimental design was carried out and values found in laboratory were compared to those of a mathematical model adjusted based on growth rate. Process efficiency was evaluated to reduce organic load, nutrient consumption, and cell count during the initial and final stages via microscopy. After the biological treatment, reduction percentages of 99% for COD (Chemical Oxygen Demand) and 95% for SS (Sedimentable Solids) were achieved, in addition to 86% and 93% of nutrient and cyanide removal, respectively, and average CO2 biofixation of 0.1854 gL-1d-1.These values are close to those found in literature for other cultivation media. It was also observed that biomass productivity and CO2 fixation data are in agreement with those obtained in other studies, thus evidencing the efficiency of Chlorella sp. microalgae and its high photosynthetic capacity.

The present study investigates the role of Chlorella sp. in the mitigation of arsenic (iAs) induced toxicity in Oryza sativa L. The study shows, co-culture of rice seedlings with Chlorella sp. reduced the iAs accumulation, simultaneously improving the growth of seedlings under iAs treatments. While treatment with As(III) and As(V) (60 µM) alone, inflicted toxicity in rice seedlings, manifested as significant enhancement in stress markers levels (TBRAS and H2O2), this coincided with the shifting of cellular reduced state to oxidized state (reduced GSH/GSSG ratio). Contrarily, co-culturing rice seedlings with Chlorella sp. under iAs toxicity, reduced these stress markers and recovered the GSH/GSSG ratio. The GSH dependent antioxidant enzymes i.e. GR and GPX activities also exhibited significant enhancement upon co-culturing rice seedlings with Chlorella sp. against iAs stress. Simultaneously, the expression of four thiol dependent GRX genes, i.e. GRX13950, GRX35340, GRX12190 and GRX07950 were enhanced against As(III) and As(V) (60 µM), which reduced upon co-culturing with Chlorella sp. A similar trend was also observed with the expression of GST genes, where the co-culture with Chlorella sp. significantly reduced the genes expression of two isoforms (GST 38600 and GST 38610). On the contrary, the expression of S-adenosylmethionine dependent methyltransferases (SAMT) gene in rice seedlings was enhanced upon co-culturing with the Chlorella sp. against iAs stress. Overall, the results demonstrate that the rice seedlings when co-culture with Chlorella sp. ameliorates iAs toxicity through GSH dependent detoxification pathway, evident from the enhanced expression of GRX, GST, SAMT genes and activity of GSH dependent antioxidant enzymes (GR and GPX) in the rice seedlings.

Microalgal technology is still economically unattractive due to the high cost associated with microalgal cultivation and biomass recovery from conventional suspension cultures. Biofilm-based cultivation is a promising alternative for higher biomass yield and cheap/easy biomass harvesting opportunities. Additionally, using anaerobic digestate food effluent (ADFE) as a nutrient source reduces the cultivation cost and achieves ADFE treatment as an added value. However, the search for locally available, inexpensive, and efficient support materials is still open to research. This study evaluates the potential of commercially available, low-cost papers as support material for biofilm cultivation of Chlorella sp. and treatment of ADFE. Among the four papers screened for microalgal attachment, quill board paper performed better in higher biomass yield and stability throughout the study period. The attached growth study was done in a modular food container vessel, using anaerobic digestate food effluent (ADFE) as a nutrient source and a basal medium as a control. The microalgae grew well on the support material with higher biomass yield and productivity of 108.64 g(DW) m -2 and 9.96 g (DW) m -2 d -1 , respectively, in the ADFE medium compared with 85.87 g (DW) m -2 and 4.99 g (DW) m -2 d -1 , respectively in the basal medium. Chlorophyll, a fluorescence (ChlF) probe, showed that cell density in the biofilm significantly changes the photosynthetic apparatus of the algae, with evidence of stress observed as the culture progressed. Also, efficient nutrient removal from the ADFE medium was achieved in the 100 %, 85 %, and 40.2 % ratios for ammoniacal nitrogen, phosphate, and chemical oxygen demand (COD). Therefore, using quill board paper as carrier material for microalgal cultivation offers promising advantages, including high biomass production, easy biomass harvesting (by scrapping or rolling the biomass with the paper), and efficient effluent 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 © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

This study explores the challenges facing microalgae biofuel production, specifically low lipid content and difficulties with algal cell harvesting. The purpose of the research is to investigate the effect of seawater content and nanoparticle concentration on freshwater microalgae growth and biofuel production. The principal results of the study show that increasing the proportion of seawater and nanoparticles enhances the lipid content and cell diameter of microalgae, while excessive concentrations of nanoparticles and low seawater content lead to reduced microalgae growth. Furthermore, an optimal cell diameter was identified at a nanoparticle concentration of 150 mg/L. The study also reveals that increasing seawater content can decrease zeta potential and increase chlorophyll a content due to the concentration of dissolved organic matter. Increasing the seawater content from 0% to 25% decreased zeta potential by 1% owing to the instability and aggregation of the cells. Chlorophyll a for the 0% seawater was 0.55 which is increased to 1.32 only due to the increase in the seawater content. This significant increase is due to the concentration of dissolved organic matter in seawater. Additionally, the presence of seawater positively affects microalgae metabolic activity and biochar yield. The findings of this study offer valuable insights into the potential for optimizing microalgae biofuel production. The use of seawater and nanoparticles has shown promise in enhancing microalgae growth and biofuel yield, and the results of this study underscore the scientific value of exploring the role of seawater and nanoparticles in microalgae biofuel production. Further research in this area has the potential to significantly contribute to the development of sustainable energy solutions., 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 © 2023 Elsevier Inc. All rights reserved.)

Microalgae act as the entrance of polybrominated diphenyl ethers (PBDEs) from abiotic to biotic environments, which controlled the environmental fate of PBDEs in aquatic environments. Combing with typical coastal environmental characteristics including extracellular polymer substances (EPS) enrichment, light limitation and nitrogen starvation, the changes of adsorption and absorption kinetics of BDE-47 by Chlorella sp. and the role of EPS therein were investigated. The results quantified the adsorption and absorption kinetics of BDE-47 by Chlorella sp. cells and fitted it by the Lagergren pseudo first order model. Furthermore, we found the adsorption and absorption kinetics could be changed by the above mentioned environmental factors. To be specific, the total BDE-47 adsorption amounts per microalgal cell were increased as the increase of ambient EPS (proteins or carbohydrates), attributing to the increase of soluble (SL)-EPS contents; increased total BDE-47 adsorption amounts but decreased absorption rates were found under light limitation and nitrogen starvation, which were attributed to increased bound (B)-EPS contents and protein/carbohydrates (P/C) ratios therein, respectively. Therefore, our study elucidated the adsorption and absorption kinetics of PBDEs by microalgae could be influenced by ambient environmental changes, clarified the roles of SL-EPS, B-EPS contents and P/C ratios, providing a solid basis for evaluating the environmental fate of PBDEs in the marine 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 © 2022 Elsevier Inc. All rights reserved.)

Chronic diabetic wound remains a critical challenge suffering from the complicated negative microenvironments, such as high-glucose, excessive reactive oxygen species (ROS), hypoxia and malnutrition. Unfortunately, few strategies have been developed to ameliorate the multiple microenvironments simultaneously. In this study, Chlorella sp. (Chlorella) hydrogels were prepared against diabetic wounds. In vitro experiments demonstrated that living Chlorella could produce dissolved oxygen by photosynthesis, actively consume glucose and deplete ROS with the inherent antioxidants, during the daytime. At night, Chlorella was inactivated in situ by chlorine dioxide with human-body harmless concentration to utilize its abundant contents. It was verified in vitro that the inactivated-Chlorella could supply nutrition, relieve inflammation and terminate the oxygen-consumption of Chlorella-respiration. The advantages of living Chlorella and its contents were integrated ingeniously. The abovementioned functions were proven to accelerate cell proliferation, migration and angiogenesis in vitro . Then, streptozotocin-induced diabetic mice were employed for further validation. The in vivo outcomes confirmed that Chlorella could ameliorate the undesirable microenvironments, including hypoxia, high-glucose, excessive-ROS and chronic inflammation, thereby synergistically promoting tissue regeneration. Given the results above, Chlorella is considered as a tailor-made therapeutic strategy for diabetic wound healing., Competing Interests: The authors have no conflicts of interest to declare., (© 2022 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.)

The intolerance of high CO 2 in the exhaust gas is the "bottleneck" limiting the wide application of microalgae for CO 2 biosequestration. Around this topic, we selected high-CO 2 -tolerant (LAMB 33 and 31) and nontolerant (LAMB 122) Chlorella strains to study their different energy metabolisms and cytoplasmic pH regulations in response to high CO 2 . Under 40 % CO 2 , LAMB 33 and 31 both showed elevated ATP synthesis, accelerated ATP consumption and fast cytoplasmic pH regulation while exhibiting different acclimating strategies therein: chloroplast acclimations were reflected by high chlorophyll contents in 33 but photosystem transitions in 31; faster mitochondrial acclimations occurred in 33 than in 31; cellular organic carbon mainly flowed to monosaccharide synthesis for 33 but to monosaccharide and protein synthesis for 31; and cytoplasmic pH regulation was attributed to V-ATPase in 31 but not in 33. All the above metabolic processes gradually collapsed in 122, leading to growth inhibition. Our study identified different metabolic acclimation strategies among Chlorella strains to high CO 2 and provided new traits for breeding microalgae for CO 2 biosequestration., 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 © 2022 Elsevier B.V. All rights reserved.)

Polybrominated diphenyl ethers (PBDEs) are toxic to marine organisms including the major primary producer phytoplankton, while the toxic mechanisms haven't yet been fully clarified. Therefore, we comprehensively studied the toxic mechanisms of BDE-47 on the marine chlorophyte Chlorella sp., with a focus on the role of cellular oxidative stress. The results indicate that BDE-47 stress resulted in the inhibition of population growth as well as cell death and programmed cell death. The antioxidant system was activated in both low and high BDE-47 treatments, but only microalgal cells in the high BDE-47 treatment showed cellular oxidative stress. By adding ROS inhibitor, the relief of photosynthetic inhibition, Ca 2+ overproduction and cell death was found. Therefore, we conclude that photosynthetic damage, cell death and cellular oxidative stress were the major mechanisms of BDE-47 toxicity to Chlorella sp., and that cellular oxidative stress played an important role in mediating the other mechanisms., (Copyright © 2021. Published by Elsevier Ltd.)

Increasing usage of both nanomaterials and pharmaceuticals and their unabated release to the marine ecosystem pose a serious concern nowadays. The toxicity of the mixture of TiO 2 NPs and tetracycline (TC) in the marine species are not very well covered in prior literature. The current study explores the joint toxic effects of TiO 2 NPs and TC in a simulated marine food chain: Chlorella sp. and Artemia salina. Chlorella sp. was interacted with pristine TiO 2 NPs (0.05, 05, and 5 mg/L), TC (0.5 mg/L), and their combinations for 48 h. The toxicity induced in Chlorella sp. by pristine TiO 2 NPs through oxidative stress and chloroplast damage was not significantly changed in the presence of TC. Principal component analysis for the toxicity parameters revealed a strong association between growth inhibition and adsorption/internalization. In the second trophic level (A. salina), the waterborne exposure of TC additively increased the toxicity of TiO 2 NPs. Both adsorption and degradation played a major role in the removal of TC from the suspension, resulting in additive toxic effects in both Chlorella sp. and A. salina. Compared to the waterborne exposure, the foodborne exposure of TiO 2 NPs and TC induced lesser toxic effects owing to reduced uptake and accumulation in A. salina. Biomagnification results indicate that the dietary transfer of TiO 2 NPs and TC does not pose a serious environmental threat in this two-level marine food chain., 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 © 2021 Elsevier B.V. All rights reserved.)

Widespread usage of nano-TiO 2 in various commercial products and their consequent release into the seawater pose a severe threat to marine biota. Nanoplastics, a secondary pollutant in the marine environment, could influence adverse effects of nano-TiO 2 . The main goal of the present study was to investigate the influence of the differently functionalized polystyrene nanoplastics (COOH-PSNPs, NH2-PSNPs, and Plain-PSNPs) on the acute toxic effects of P25 nano-TiO 2 in marine algae Chlorella sp. Three different concentrations of nano-TiO 2 , 0.25, 0.5, and 1 mg/L, mixed with 5 mg/L of the PSNPs were employed in this study. A substantial increase was noted in mean hydrodynamic sizes of nano-TiO 2 when they were mixed with the PSNPs. This hetero-aggregation would reduce the bioavailability of the particles to the algae. The presence of the PSNPs in the mixture reduced the toxicity of nano-TiO 2 significantly. A signficant decline in the oxidative stress parameters like total ROS, superoxide (), and hydroxyl radical generation was noted for the mixture of nano-TiO 2 with the PSNPs in comparison with the pristine counterparts. The lipid peroxidation, and the antioxidant enzyme activities in the cells correlated well with the reactive species generation results. The treatments with the mixture resulted in notable enhancement in the esterase activity in the cells. The Independent Action model suggested antagonistic interactions between PSNPs and nano-TiO 2 . The results from this study clearly demonstrate that nano-TiO 2 in presence of the PSNPs exerted significantly reduced cytotoxic effects in Chlorella sp, in comparison with the pristine particles., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The rising use of contaminants such as nanoparticles and microplastics has taken a heavy toll on the marine environment. However, their combined toxic effects on the species across various trophic levels remain quite unexplored. The aim of this study was to explore the effects of three surface-functionalized (carboxylated, plain, and aminated) polystyrene microplastics on nano-TiO 2 toxicity across two trophic levels containing Chlorella sp. as the prey and Artemia salina as the predator. The experiments carried out on Chlorella sp. include the toxicity assessment, oxidative stress determination, and uptake of nano-TiO 2 (both in the presence and absence of microplastics). Results revealed that the aminated and plain polystyrene microplastics enhanced nano-TiO 2 toxicity, while carboxylated microplastics decreased the toxic effects in Chlorella sp. On the other hand, toxicity assessment in Artemia salina was carried out using two different modes of exposure: aqueous and dietary routes. The aqueous route involving the direct exposure of nano-TiO 2 and microplastics indicated greater toxicity, uptake, and accumulation in Artemia salina than the dietary route of exposure. Since dietary exposure decreased the toxicity, uptake, and accumulation of nano-TiO 2 , no change (p > 0.05) in the biomagnification factors of nano-TiO 2 was noted for all the test concentrations of nano-TiO 2 combined with and without microplastics. The computed values were less than 1, indicating negligible transfer of nano-TiO 2 from Chlorella sp. to Artemia salina. Overall, the study highlights the two-level trophic toxicity and the transfer potential of nano-TiO 2 under the influence of different microplastics., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The successful cultivation of microalgae in wastewater establishes a waste to profit scenario as it combines treatment of a waste stream with production of valuable end-products. Here, growth and nutrient removal efficiency of three different locally isolated microalgal cultures (Chlorella sp., Scenedesmus sp., and a mixed consortium) cultivated in anaerobically digested municipal centrate (ADMC) and anaerobically digested abattoir effluent (ADAE) was evaluated. No significant differences (P > 0.05) in specific growth rate and biomass productivity were recorded between Chlorella monocultures and the mixed culture grown in both effluents. Scenedesmus sp. monocultures was found incapable of growth in both ADMC and ADAE throughout the cultivation period resulting in the collapse of cultures and no further measurements on the growth, biomass production and nutrient removal efficiency of this alga in both effluent. F q ´/F m ´ values which represent the immediate photo-physiological status of microalgae found to be negatively inhibited when Scenedesmus sp. was grown in both effluents throughout the cultivation period. F q ´/F m ´ values of Chlorella sp. monocultures and the mixed cultures recovered back to normal (≈0.6) after an initial drop. Ammonium removal rates was found to be significantly higher (≈2 folds) for Chlorella sp. monocultures grown in both ADMC and ADAE when compared to the mixed cultures. Nonetheless, no significant differences were observed in the removal of phosphate for both cultures in the different effluents. The total protein and carbohydrate content of the biomass produced was similar for both microalgae cultures grown using ADAE and ADMC. However, chlorophyll a and total carotenoids content were found to be higher (P < 0.05) for the cultures grown in ADAE than ADMC. Overall, Chlorella sp. monoculture was the most efficient option for treating both ADMC and ADAE while simultaneously generating protein rich biomass (up to 49%) that can be potentially exploited as aquaculture feedstock., 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 © 2021 Elsevier B.V. All rights reserved.)

High CO 2 acclimation for microalgae has attracted large research attention owing to the usefulness of microalgae in bio-sequestration of CO 2 from the emission source. In this study, one high CO 2 tolerant (LAMB 31) and non-tolerant (LAMB 122) Chlorella sp. strains were transferred from air to 40% CO 2 , during which four time points were chosen for comparative transcriptome analysis. Gene changes started in the lag phase (T1) of population growth with more genes (7889) upregulated in LAMB 31 than in LAMB 122 (1092). Further function enrichments indicated: In LAMB 31, up-regulation of genes in cyclic electron transportation, F-type ATPase and Calvin cycle were associated with the enhancement of carbon fixation abilities; upregulation of genes in phosphorylation together with V-ATPase, which contributed to cytoplasmatic pH stability; Lastly, enhancement of carbon metabolisms including TCA cycle and glycolysis accelerated the consumption of cellular organic carbon. Most of the genes in these pathways and processes showed downregulation in LAMB 122. This study disclosed the most complete transcriptional molecular mechanisms of Chlorella sp. responding to high CO 2 by combining CO 2 fixation, transportation, and metabolic processes. The results provided valuable genetic information for future screening and breeding of microalgae with high-CO 2 tolerance for more efficient CO 2 bio-sequestration., 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 © 2020 Elsevier B.V. All rights reserved.)

Algal productivity in steady-state cultivation systems depends on important factors such as biomass concentration, solids retention time (SRT), and light intensity. Current modeling of algal growth often ignores light distribution in algal cultivation systems and does not consider all these factors simultaneously. We developed a new algal growth model using a first principles approach to incorporate the effect of light intensity on algal growth while simultaneously considering biomass concentration and SRT. We first measured light attenuation (decay) with depth in an indoor algal membrane bioreactor (A-MBR) cultivating Chlorella sp. We then simulated the light decay using a multi-layer approach and correlated the decay with biomass concentration and SRT in model development. The model was calibrated by delineating specific light absorptivity and half-saturation constant to match the algal biomass concentration in the A-MBR operated at a target SRT. We finally applied the model to predict the maximum algal productivity in both indoor and outdoor A-MBRs. The predicted maximum algal productivities in indoor and outdoor A-MBRs were 6.7 g·m -2 ·d -1 (incident light intensity 5732 lx, SRT approximately 8 d) and 28 g·m -2 ·d -1 (sunlight intensity 28,660 lx, SRT approximately 4 d), respectively. The model can be extended to include other factors (e.g., water temperature and carbon dioxide bubbling) and such a modeling framework can be applied to full-scale, continuous flow outdoor systems to improve algal productivity., 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 © 2020 Elsevier B.V. All rights reserved.)

The present study investigates the role of Chlorella sp. in the mitigation of arsenic (iAs) induced toxicity in Oryza sativa L. The study shows, co-culture of rice seedlings with Chlorella sp. reduced the iAs accumulation, simultaneously improving the growth of seedlings under iAs treatments. While treatment with As (III) and As (V) (60 µM) alone, inflicted toxicity in rice seedlings, manifested as significant enhancement in stress markers levels (TBRAS and H 2 O 2 ), this coincided with the shifting of cellular reduced state to oxidized state (reduced GSH/GSSG ratio). Contrarily, co-culturing rice seedlings with Chlorella sp. under iAs toxicity, reduced these stress markers and recovered the GSH/GSSG ratio. The GSH dependent antioxidant enzymes i.e. GR and GPX activities also exhibited significant enhancement upon co-culturing rice seedlings with Chlorella sp. against iAs stress. Simultaneously, the expression of four thiol dependent GRX genes, i.e. GRX13950, GRX35340, GRX12190 and GRX07950 were enhanced against As (III) and As (V) (60 µM), which reduced upon co-culturing with Chlorella sp. A similar trend was also observed with the expression of GST genes, where the co-culture with Chlorella sp. significantly reduced the genes expression of two isoforms (GST 38600 and GST 38610). On the contrary, the expression of S-adenosylmethionine dependent methyltransferases (SAMT) gene in rice seedlings was enhanced upon co-culturing with the Chlorella sp. against iAs stress. Overall, the results demonstrate that the rice seedlings when co-culture with Chlorella sp. ameliorates iAs toxicity through GSH dependent detoxification pathway, evident from the enhanced expression of GRX, GST, SAMT genes and activity of GSH dependent antioxidant enzymes (GR and GPX) in the rice seedlings., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Bioconversion of food waste into value-added products is a promising way to tackle the global food waste management problem. In this study, a novel valorisation strategy for bioenergy and lutein production via microalgal fermentation was investigated. Significant amount of glucose was recovered from enzymatic hydrolysis of food waste. The resultant hydrolysate was then utilised as culture medium in mixotrophic cultivation of Chlorella sp. to obtain high levels of lipid and lutein, whose accumulation patterns were consistent with molecular analyses. The resultant algal lipid derived from microalgal biomass using food hydrolysate was at high quality in terms of biodiesel properties. Further, in semi-continuous fermentation, the average algal biomass was 6.1 g L -1 with 2.5 g L -1 lipid and 38.5 mg L -1 lutein using hydrolysate with an initial glucose concentration of 10 g L -1 . Meanwhile, the resultant algal biomass was 6.9 g L -1 with 1.8 g L -1 lipid and 63.0 mg L -1 lutein using hydrolysate with an initial glucose concentration of 20 g L -1 , which suggests food waste hydrolysate could trigger algal products preferences. The experimental results of this study suggested the potential of microalgae as a platform for bioconversion of food waste into high-value products, especially sustainable bioenergy., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Functional diversity/distinctness measure based trait has been proved to be a robust indicator to summarize the description of community structures and to assess water quality in different types of aquatic environment. In this study, for identifying the shielding effect of microalgae against protozoan grazing, a nine-day survey was conducted by exposing protozoan communities to a series of concentration gradients (10 0 (control), 10 4 , 10 5 , 10 6 and 10 7  cells ml -1 ) of two microalgae, respectively. Our results showed clear resistance of two test microalgae against protozoan grazing in five treatments. The functional distinctness measures commonly represented a decreasing trend along the gradient of concentrations of both microalgae. Ellipse tests based on the paired functional distinctness indices revealed that community functioning represented an uptrend departure from the expected pattern with the concentrations of both microalgae increase. Therefore, we suggest that the functional distinctness measures might be a reliable approach to detect the ecological effect of microalgae against protozoan grazing., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Polybrominated diphenyl ethers (PBDEs) are a series of important persistent organic pollutants (POPs) in marine environments. Microalgae are the start of PBDEs bioaccumulated and bioconcentrated along the marine food web. In order to investigate the variations of PBDEs bioaccumulation by microalgae and its influencing factors, we set up a series of experiments with Chlorella sp. under different BDE-47 or BDE-209 exposure modes to measure their toxicity, bioaccumulation and degradation patterns. The inhibition effect on cell growth was much more obvious in BDE-47 than BDE-209, with the EC 50 values at 96 h calculated as 64.7 μg L -1 and 4070 μg L -1 , respectively. Microalgal uptake rates showed BDE-209 diffused less into cells than BDE-47, with highest measured uptake rates of 0.145 × 10 -7  μg h -1 cell -1 and 0.45 × 10 -7  μg h -1 cell -1 , respectively. The bioaccumulation amount by unit microalgal cell varied with PBDE concentrations and culture time, which appeared to be related to the changes of extracellular polymeric substances (EPS) and cellular neutral lipids under the toxicity of PBDEs. Finally, we found Chlorella sp. delayed the debromination patterns of BDE-209 compared to seawater. This study linked the toxicity, microalgal bioaccumulation and metabolism of PBDEs, provided new insights in the research of POPs by microalgae and marine food webs., 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 © 2020 Elsevier B.V. All rights reserved.)

In the environment, arsenic (As) exists in a number of chemical species, and arsenite (As(III)) and arsenate (As(V)) dominate in freshwater systems. Toxicity of As species to aquatic organisms is complicated by their interaction with chemicals in water such as phosphate that can influence the bioavailability and uptake of As(V). In the present study, the toxicities of As(III), As(V) and dimethylarsinic acid (DMA) to three freshwater organisms representing three phylogenetic groups: a phytoplankton (Chlorella sp. strain CE-35), a floating macrophyte (Lemna disperma) and a cladoceran grazer (Ceriodaphnia cf. dubia), were determined using acute and growth inhibition bioassays (EC₅₀) at a range of total phosphate (TP) concentrations in OECD medium. The EC₅₀ values of As(III), As(V) and DMA were 27 ± 10, 1.15 ± 0.04 and 19 ± 3 mg L(-1) for Chlorella sp. CE-35; 0.57 ± 0.16, 2.3 ± 0.2 and 56 ± 15 mg L(-1) for L. disperma, and 1.58 ± 0.05, 1.72 ± 0.01 and 5.9 ± 0.1 mg L(-1) for C. cf. dubia, respectively. The results showed that As(III) was more toxic than As(V) to L. disperma; however, As(V) was more toxic than As(III) to Chlorella sp. CE-35. The toxicities of As(III) and As(V) to C. cf. dubia were statistically similar (p>0.05). DMA was less toxic than iAs species to L. disperma and C. cf. dubia, but more toxic than As(III) to Chlorella sp. CE-35. The toxicity of As(V) to Chlorella sp. CE-35 and L. disperma decreased with increasing TP concentrations in the growth medium. Phosphate concentrations did not influence the toxicity of As(III) to either organism. Chlorella sp. CE-35 showed the ability to reduce As(V) to As(III), indicating a substantial influence of phytoplankton on As biogeochemistry in freshwater aquatic systems., (Copyright © 2014 Elsevier Inc. All rights reserved.)