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Chlorella sorokiniana (CS) is a prominent microalga with vast potential as a biocarrier for carbon mitigation toward a green process. However, challenges remain in achieving high biomass levels and production rates. Therefore, a systematic feeding strategy using 4-aminobutyric acid (GABA) and CRISPR technology was applied to improve microalgal productivity. At first, GABA increased protein content by 1.4-fold, while intermittent supplementation during cultivation resulted in a 1.58-fold and 2.13-fold increase in biomass and pigment content, respectively. Under halophilic conditions, the optimal approach involved repeated feeding of 5 mM GABA at the initial and mid-log phases of growth, resulting in biomass, protein, and pigment levels of 6.74 g/L, 3.24 g/L, and 49.87 mg/L. CRISPRa mediated glutamate synthase and using monosodium glutamate (MSG) as a cheap precursor for GABA has effectively enhanced the biomass, protein, and lutein content, thus offers a cost-effective approach to commercialize high-valued chemical using algae towards a low-carbon paradigm., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors are grateful for the financial support received from the Ministry of Science and Technology (MOST 110-2221-E-006-030-MY3 and MOST 111-2221-E-006-012-MY3) and National Science and Technology Council (NSTC 112-2218-E006-022) in Taiwan., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Microalgae are widely recognized as a promising bioresource for producing renewable fuels and chemicals. Microalgal biorefinery has tremendous potential for incorporation into circular bioeconomy, including sustainability, cascading use, and waste reduction. In this study, genetic engineering was used to enhance the growth, lipid and lutein productivity of Chlamydomonas reinhardtii including strains of CC400, PY9, pCHS, and PG. Notably, CRISPRi mediated on phosphoenolpyruvate carboxylase (PEPC1) gene to down-regulate the branch pathway from glycolysis to partitioning more carbon flux to lipid was explored under meso-thermophilic condition. The best chassis PGi, which has overexpressed chaperone GroELS and applied CRISPRi resulting in the highest biomass of 2.56 g/L and also boosted the lipids and lutein with 893 and 23.5 mg/L, respectively at 35°C. Finally, all strains with CRISPRi exhibited higher transcriptional levels of the crucial genes from photosynthesis, starch, lipid and lutein metabolism, thus reaching a CO 2 assimilation of 1.087 g-CO 2 /g-DCW in mixotrophic condition., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors are grateful for the financial support received from the Ministry of Science and Technology (MOST 110-2221-E-006-030-MY3 and NSTC 111-2221-E-006-012-MY3) in Taiwan., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Carbon dioxide is the major greenhouse gas and regards as the critical issue of global warming and climate changes. The inconspicuous microalgae are responsible for 40% of carbon fixation among all photosynthetic plants along with a higher photosynthetic efficiency and convert the carbon into lipids, protein, pigments, and bioactive compounds. Genetic approach and metabolic engineering are applied to accelerate the growth rate and biomass of microalgae, hence achieve the mission of carbon neutrality. Meanwhile, CRISPR/Cas9 is efficiently to enhance the productivity of high-value compounds in microalgae for it is easier operation, more affordable and is able to regulate multiple genes simultaneously. The genetic engineering strategies provide the multidisciplinary concept to evolute and increase the CO 2 fixation rate through Calvin-Benson-Bassham cycle. Therefore, the technologies, bioinformatics tools, systematic engineering approaches for carbon neutrality and circular economy are summarized and leading one step closer to the decarbonization society in this review., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors are grateful for the financial support received from the Ministry of Science and Technology to I-Son Ng (MOST 111-2221-E-006-012-MY3 and MOST 110-2221-E-006-030-MY3) and to Tse-Min Lee (MOST 110-2311-B-110 -003, MOST 111-2311-B-110-002, MOST 111-2923-B-110 -001-MY2, and MOST 110-2622-E-110-016) in Taiwan., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Excessive carbon dioxide (CO 2 ) emissions into the atmosphere have become a dire threat to the human race and environmental sustainability. The ultimate goal of net zero emissions requires combined efforts on CO 2 sequestration (natural sinks, biomass fixation, engineered approaches) and reduction in CO 2 emissions while delivering economic growth (CO 2 valorization for a circular carbon bioeconomy, CCE). We discuss microalgae-based CO 2 biosequestration, including flue gas cultivation, biotechnological approaches for enhanced CO 2 biosequestration, technological innovations for microalgal cultivation, and CO 2 valorization/biofuel productions. We highlight challenges to current practices and future perspectives with the goal of contributing to environmental sustainability, net zero emissions, and the CCE., Competing Interests: Declaration of interests The authors declare no conflicts of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Chlorella species are indispensable microalgae for biorefinery but are hardly in DNA manipulation due to the high guanine-cytosine (GC) contents of DNA. In this study, we established a new approach via 20 guanines for sgRNA design, which is annotated as "Adaptive Single Guide Assisted Regulation DNA (ASGARD)" and coupling with CRISPR interference associated dCas9 system to overcome the difficulties. At first, C. sorokiniana was predominate as its faster growth rate when compared to C. vulgaris and C. variabilis in the culture using Tris-acetate-phosphate (TAP) medium. Among all the genetic transformants, gene regulation via CRISPRa-VP64 (CRISPRa) enhanced the protein contents up to 60% (w/w) of dry cell weight, where the highest concentration was 570 mg L -1 . Meanwhile, CRISPRi-KRAB (CRISPRi) with ASGARD increased protein content to 65% and lipid formed in the range of 150-250 mg L -1 . From the transcriptome analysis, we deciphered 468 genes down-regulated and 313 genes up-regulated via CRISPRi, while less difference existed in CRISPRa. This novel design and technology reveal a high potential of gene-regulating approach to other species for the biorefinery and bio-industry., (© 2021 Wiley-VCH GmbH.)

The 4-aminobutyric acid (GABA) is important to produce bio-nylon 4 in biorefineries. First, a glutamate decarboxylase (GAD) was propagated in three different Escherichia coli strains to achieve 100% conversion from 1 M monosodium glutamate after optimization of the process. To make the process greener and more efficient, in situ CO 2 adaptation and citrate feeding strategies to maintain the optimal pH value and 498 g/L of GABA was obtained. However, the process releases the equivalent amount of CO 2 . Therefore, CO 2 generated from GABA production was completely sequestered in sodium hydroxide to form bicarbonate and applied in a coupling culture of Chlorella sorokiniana (CS) or Chlorella vulgaris (CV) to increase the biomass when combined with sodium bicarbonate and carbonic anhydrase. Further improvement of 1.65-fold biomass and 1.43-fold lipid content were occurred when supplying GABA to the culture. This integrative process provided the highest GABA production rate without CO 2 release, forming an eco-friendly and carbon-neutral technology., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This work aimed to study the efficiency of polyvinyl-alcohol-immobilized Actinobacillus succinogenes ATCC55618 for succinic acid (SA) production. Batch fermentation (pH 7, 45% CO 2 gas at 0.04 vvm) using glucose (40 g L -1 ) resulted in SA titer, 26.7 g L -1 ; productivity, 3.33 g L -1 h -1 ; yield, 0.621 g g - 1. Fed-batch mode with cyclic extrication of SA from the medium markedly enhanced the yield to 0.699 g g -1 and concentration to 59.5 g L -1 . Batch fermentation using sugars derived from Chlorella vulgaris ESP-31 without yeast extract gave a SA productivity, concentration, and yield of 1.82 g L -1 h -1 , 36.1 g L -1 , and 0.720 g g - 1, respectively. Furthermore, continuous fermentation (at 6 h HRT) with microalgal sugar improved the productivity and yield to 3.53 g L -1 h -1 and 0.62 g g -1 , respectively, which is comparable to those obtained by using glucose. This study reports the highest productivity for SA fermentation using microalgae-derived sugars., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Microalgae-based bioproducts are in limelight because of their promising future, novel characteristics, the current situation of population needs, and rising prices of rapidly depleting energy resources. Algae-based products are considered as clean sustainable energy and food resources. At present, they are not commercialized due to their high production cost and low yield. In recent years, novel genome editing tools like RNAi, ZNFs, TALENs, and CRISPR/Cas9 are used to enhance the quality and quantity of the desired products. Genetic and metabolic engineering are frequently applied because of their rapid and precise results than random mutagenesis. Omic approaches help enhance biorefinery capabilities and are now in the developing stage for algae. The future is very bright for transgenic algae with increased biomass yield, carbon dioxide uptake rate, accumulating high-value compounds, reduction in cultivation, and production costs, thus reaching the goal in the global algal market and capital flow. However, microalgae are primary producers and any harmful exposure to the wild strains can affect the entire ecosystem. Therefore, strict regulation and monitoring are required to assess the potential risks before introducing genetically modified microalgae into the natural ecosystem., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Being the green gold of the future, microalgae and cyanobacteria have recently attracted considerable interest worldwide, for their metabolites such as lipids, protein, pigments, and bioactive compounds have immense potential for sustainable energy and pharmaceutical production capabilities. In the last decades, the efforts attended to enhance the usage of microalgae and cyanobacteria by genetic manipulation, synthetic and metabolic engineering. However, the development of photoautotrophic cell factories have rarely compared to the heterotrophic counterparts due to limited tools, bioinformatics, and multi-omics database. Therefore, recent advances of their genome editing techniques by clustered regularly interspaced short palindromic repeats (CRISPR) technology, and potential applications of their metabolic engineering and regulation approaches are examined in this review. Moreover, the contemporary achievements of synthetic biology approaches of microalgae and cyanobacteria in carbon fixation and sequestration, lipid and triacylglycerol (TAG), and sustainable production of high value-added chemicals, such as carotenoids and docosahexaenoic acid (DHA), have been also discussed. From recent genomic study to trends in metabolic regulation of microalgae and cyanobacteria and a comprehensive assessment of the current challenges and opportunities for microalgae and cyanobacteria is also conducted., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lactic acid (LA) fermentation was conducted with suspended and immobilized cells of an isolated Lactobacillus plantarum 23 strain using various fermentation strategies. Glucose and an alternative, relatively inexpensive carbon source - the hydrolysate of microalga Chlorella vulgaris ESP-31, were used as the carbon source. Batch fermentation using immobilized cells of L. plantarum 23 could enhance LA titer and yield by 43% and 39%, respectively, when compared with the suspended culture. Fed-batch culture integrated with in situ LA removal via ion exchange raised LA productivity by 72% by overcoming product inhibition. The highest LA productivity from glucose with PVA immobilized cells was 14.22 g/L/h, achieved under continuous operation at 50% w/v loading of immobilized beads and hydraulic retention time (HRT) of 2 h. PVA immobilized L. plantarum 23 could also use microalgal hydrolysate as the renewable carbon source, and the highest LA productivity was 9.93 g/L/h under continuous fermentation at 4 h HRT., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Microalgae and cyanobacteria are easy to culture, with higher growth rates and photosynthetic efficiencies compared to terrestrial plants, and thus generating higher productivity. The concept of microalgal biorefinery is to assimilate carbon dioxide and convert it to chemical energy/value-added products, such as vitamins, carotenoids, fatty acids, proteins and nucleic acids, to be applied in bioenergy, health foods, aquaculture feed, pharmaceutical and medical fields. Therefore, microalgae are annotated as the third generation feedstock in bioenergy and biorefinery. In past decades, many studies thrived to improve the carbon sequestration efficiency as well as enhance value-added compounds from different algae, especially via genetic engineering, synthetic biology, metabolic design and regulation. From the traditional Agrobacterium-mediated transformation DNA to novel CRISPR (clustered regularly interspaced short palindromic repeats) technology applied in microalgae and cyanobacteria, this review has highlighted the genome editing technology for biorefinery that is a highly environmental friendly trend to sustainable and renewable development., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this study, productions of microalgal proteins were explored via a circular economy concept. First, production of proteins from Chlorella vulgaris FSP-E (CV) and Chlorella sorokiniana (CS) was optimized by using favorable cultivation conditions and strategies. The optimal CO 2 concentration for the growth of both microalgae was 5% (v/v), while the optimal nitrogen source for CV and CS were 12 mM of NaNO 3 and NH 4 Cl, respectively. Addition of 12 mg/L ammonium iron (III) citrate enhanced protein production. Next, semi-batch cultivation strategy was employed to achieve a protein production of 793.3 and 812.8 mg/L for CV and C S, representing a 4.86 and 2.77 fold increase, respectively, in protein productivity. The obtained microalgal proteins consist of 40% essential amino acids. The CV and CS proteins possess prebiotic activities as they enhanced the growth of Lactobacillus rhamnosus ZY by 48 and 74%, respectively, with a good antibacterial activity against predominant pathogens., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Microalgae serve as a promising source for the production of biofuels and bio-based chemicals. They are superior to terrestrial plants as feedstock in many aspects and their biomass is naturally rich in lipids, carbohydrates, proteins, pigments, and other valuable compounds. Due to the relatively slow growth rate and high cultivation cost of microalgae, to screen efficient and robust microalgal strains as well as genetic modifications of the available strains for further improvement are of urgent demand in the development of microalgae-based biorefinery. In genetic engineering of microalgae, transformation and selection methods are the key steps to accomplish the target gene modification. However, determination of the preferable type and dosage of antibiotics used for transformant selection is usually time-consuming and microalgal-strain-dependent. Therefore, more powerful and efficient techniques should be developed to meet this need. In this review, the conventional and emerging genome-editing tools (e.g., CRISPR-Cas9, TALEN, and ZFN) used in editing the genomes of nuclear, mitochondria, and chloroplast of microalgae are thoroughly surveyed. Although all the techniques mentioned above demonstrate their abilities to perform gene editing and desired phenotype screening, there still need to overcome higher production cost and lower biomass productivity, to achieve efficient production of the desired products in microalgal biorefineries., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Microalgal biomass as renewable energy source is believed to be of great potential for reliable and sustainable biofuels production. However, microalgal biomass production is pinned by harvesting and dewatering stage thus hindering the developing and growing microalgae biotechnology industries. Flotation technology applied in mineral industry could be potentially applied in microalgae harvesting and dewatering, however substantial knowledge on different flotation units is essential. This paper presents an overview on different flotation units as promising cost-effective technologies for microalgae harvesting thus bestowing for further research in development and commercialization of microalgae based biofuels. Dispersed air flotation was found to be less energy consuming. Moreover, Jameson cell flotation and dispersed ozone flotation are believed to be energy efficient microalgae flotation approaches. Microalgae harvesting and dewatering by flotation is still at embryonic stage, therefore extended studies with the focus on life cycle assessment, sustainability of the flotation unit, optimization of the operating parameters using different algal species is imperative. Though there are a number of challenges in microalgae harvesting and dewatering, with well designed and developed cultivation, harvesting/dewatering, extraction and conversion technologies, progressively, microalgae technology will be of great potential for biological carbon sequestration, biofuels and biochemicals production., (Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Highlights • An exogenous CA was expressed in microalgae for the first time. • The highest biomass was obtained in a two-layer Photo Reactor with CO 2 supply. • Decrease in GS gene expression reduced protein and chlorophyll content. • Decrease in PEPC gene expression elevated lipid production. • Expression of exogenous MlCA gene in microalgae changes the cell morphology. Abstract Increasing atmospheric carbon dioxide (CO 2) has led to a series of problems, impacting both our lives and environment. One of the solutions to capture and reduce CO 2 is by carbon capture and storage (CCS). Carbonic anhydrase (CA) is an ancient enzyme existing in most organisms and it catalyzes the interconversion of CO 2 and bicarbonate (HCO 3 −). Therefore, overexpression of CA in microalgae could be a potential way to capture excess CO 2 in an effective manner. In this study, an exogenous MlCA gene (i.e. , 678 bp) which has been reported with highest catalytic activity was successfully overexpressed in Chlorella sorokiniana (CS) and Chlorella vulgaris (CV), respectively. The genetically engineered algae harboring exogenous CA were cultured in a specially designed Two-layer Photo Reactor (TPR) for validation. Transgenic algae with MlCA had improved biomass production, protein content and lipid accumulation. Finally, the transformants obtained a higher lipid amount up to 1.1 g/L which was 2.2-fold than that of wild types as well as accelerating the carbon capture and fixation. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this study, CRISPRi (clustered regularly interspaced short palindromic repeats interference) was used for the first time to regulate expression of exogenously supplied rfp gene as a proof-of-concept, and endogenous PEPC1 gene as a proof-of-function in Chlamydomonas reinhardtii . The efficiency of 94% and stability of 7 generations via CRISPRi mediated gene regulation in C. reinhardtii have been demonstrated by RFP. Gene PEPC1 encoding proteins are essential for controlling the carbon flux that enters the TCA cycle and plays a crucial role in carbon partitioning of substrates in competition with lipid synthesis. All CrPEPC1 down-regulated strains have lower chlorophyll color, but higher biomass concentration and lipid accumulation rate. The present results revealed that CRISPRi based transcriptional silencing was applicable in C. reinhardtii and expanded the way to improve the yield, titer and productivity of microalgae-based products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bicarbonate is a superior and economic carbon source for microalgal carbon fixation. • Algal CCMs play a crucial role in bicarbonate utilization. • Algae-driven carbonate-based carbon capture/utilization and waste treatment are outlined. • Bicarbonate-based microalgae cultivation has technical hurdles for wide applications. • Strategies, current challenges, prospects, and future research directions are discussed. Conventional carbon fixation by microalgae involves the direct introduction of CO 2 as the carbon source for microalgal growth. However, CO 2 displays low solubility in water and a low mass transfer rate into microalgal cells, limiting the efficiency of CO 2 capture. Microalgae production using bicarbonate-based cultivation has gained significant attention recently due to its potential applications in biofuel production, wastewater treatment, and carbon capture. Microalgae can uptake and assimilate bicarbonate as an inorganic carbon source based on their capability for intracellular and extracellular interconversion of carbon dioxide and bicarbonate. This interconversion, catalyzed by carbonic anhydrases, is an integral part of carbon acquisition using carbon concentrating mechanisms. In contrast to photoautotrophic growth using CO 2 , the pH of the culture medium increases significantly during bicarbonate assimilation. Thus, pH-stat cultivation needs to be adapted to attain maximal biomass production. Other strategies, such as optimization of bicarbonate concentration, combining bicarbonate as an additional carbon source in mixotrophic cultivation, and bicarbonate supplementation in wastewater treatment, can be applied to harness the potential of a highly soluble inorganic carbon source in an algal culture system. This comprehensive review presents bicarbonate-based microalgal cultivation technologies, particularly their underlying mechanisms, benefits and challenges, essential strategies, and prospective outlook. Prospective avenues for future research are outlined to support the advancement of cost-effective and green, microalgae-based integrated carbon capture, biofuel generation, high-value biochemical production, and wastewater treatment systems, thereby promoting a circular and sustainable net-zero carbon society. [ABSTRACT FROM AUTHOR]

[Display omitted] • A two-stage cultivation strategy can increase both biomass and target product yield. • Sequential and multi-component extraction lead to downstream resource efficiency. • Seawater, wastewater, and recycled nutrients are crucial in maintaining efficiency. • Integrative design navigates trade-offs between environmental and economic aspects. • Life Cycle Costing and Sustainability Assessment broaden well-to-wheel analysis. Microalgae hold tremendous potential as sustainable bioresources in carbon capture, climate change mitigation, and the development of net-zero lifestyles. However, scaling up microalgae cultivation necessitates overcoming obstacles in strain selection, bioreactor design, and cultivation strategies. While microalgae were initially viewed as a simple biomass feedstock for energy security, emerging applications such as wastewater bioremediation, carbon capture, and the production of valuable chemicals have reshaped the overall perspective of microalgae. Exciting advancements in microalgal genetic engineering, encompassing evolutionary approach, CRISPR technology, modular cloning toolkits, and bioinformatics, pave the way for optimizing productivity and minimizing environmental footprints. This review delves into crucial aspects of microalgae cultivation, including harvesting, cell disruption, and waste valorization. Additionally, new understandings of integrative design and life-cycle assessment are discussed alongside the promise of bioenergy production, providing the current stage of development and challenges to handle. Ultimately, this review offers new perspectives on microalgal biotechnology aiming to contribute to an eco-friendly green paradigm. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A mutant strain C. sorokiniana MB-1-M12 was cultivated outdoors for lutein production. • Lutein production is better with semi-continuous operation compared to fed-batch operation. • Simulated outdoor cultivation yielded a high lutein productivity of 3.34 mg/L/d. • Productivity was enhanced to 4.46 mg/L/d in outdoor cultivation with 60 L PBRs. • Strain MB-1-M12 is suitable for outdoor large-scale cultivation for lutein production. Abstract A lutein-enriched mutant, Chlorella sorokiniana MB-1-M12 was grown mixotrophically for lutein production. The lutein production efficiency of the strain was enhanced via optimizing the operating strategies. The results show that using semi-continuous cultivation with a medium replacement ratio of 75% resulted in a higher lutein productivity and lutein concentration of 6.24 mg/L/d and 50.6 mg/L, respectively, which were markedly higher than those obtained from batch and fed-batch cultivation. Cultivation under simulated outdoor cultivation conditions (i.e., temperature of 35 °C/25 °C for a 12 h/12 h light/dark cycle) could achieve the highest lutein productivity and lutein concentration of 3.34 mg/L/d and 30.8 mg/L, respectively. Lutein production via outdoor cultivation of MB-1-M12 strain with a 60-L tubular photobioreactor was performed using semi-continuous operation. With a medium replacement ratio of 75%, a good lutein productivity (4.46 mg/L/d) and concentration (27.4 mg/L) was obtained, indicating the feasibility of producing lutein under outdoor cultivation of the microalgal strain. [ABSTRACT FROM AUTHOR]

A heterotrophic mutant of Chlorella sorokiniana MB-1-M12 was evaluated for its ability to produce lutein using organic carbon and nitrogen sources and without light irradiation. In batch fermentation, the maximal lutein content (3.67 mg lutein/g biomass) and productivity (2.84 mg/L/d) could be obtained when cultivated in BG-11 medium with 7.5 g/L glucose, 0.75 g/L urea, pH 7.5 and a C/N ratio of 10. A novel two-stage cultivation strategy that integrates fed-batch and semi-batch operations was applied to enhance the lutein production performance. When growing MB-1-M12 strain in a 5L fermenter using the optimal operation strategies, the maximum biomass concentration, biomass productivity, lutein content and lutein productivity could reach 25 g/L, 4.88 mg/L/d, 5.88 mg/g and 16.2 mg/L/d, respectively. This high lutein productivity could significantly reduce the cultivation time and the associated costs, indicating the potential of using MB-1-M12 strain for heterotrophic lutein production in commercial scale. [ABSTRACT FROM AUTHOR]

Six methods for microalgal cell disruption were compared for the optimization of carotenoids extraction from the lutein-rich thermo-tolerant microalga Desmodesmus sp. F51. Among them, both bead-beating and high pressure homogenization (HPH) were found to have potential to disrupt Desmodesmus sp. F51 cells with high efficiency, but this study focused only on HPH treatment. Effects of homogenization pressure, cycle number and cell density on cell disruption efficiency were investigated. The degree of cell disruption increased with increasing high homogenization pressure (10–40 kpsi) and cycle number (1–4). Cell density in the range of 2.0–90 g/L did not affect the performance of cell disruption process, while a higher specific energy consumption arised when using a lower cell concentration. The HPLC analysis showed that the main carotenoids present in Desmodesmus sp. F51 were neoxanthin, violaxanthin, lutein, α-carotene and β-carotene. Moreover, the developed HPH model could well describe the cell disruption behavior at various high homogenization pressures (10–40 kpsi) and cycle numbers (1–4). The obtained parameters indicate that homogenization pressure is a more significant factor than cycle number in achieving high cell disruption efficiency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Lutein production of Desmodesmus sp. F51 was enhanced with fed-batch cultivation. [•] Fed-batch culture controlling both medium feeding and illumination gave best results. [•] Lutein accounted for 50–66% of the total carotenoids in the microalgal biomass. [•] Repeated fed-batch operations improved both CO2 fixation and lutein production. [ABSTRACT FROM AUTHOR]

Four indigenous thermo-tolerant Desmodesmus sp. strains were examined for their ability to produce lutein. Among them, Desmodesmus sp. F51 was the best strain for this purpose. The medium composition, nitrate concentration and light intensity were manipulated to improve the phototrophic growth and lutein production of Desmodesmus sp. F51. It was found that a nitrogen-sufficient condition was required for lutein accumulation, while a high light intensity enhanced cell growth but caused a decrease in the lutein content. The best cell growth and lutein production occurred when the light intensity and initial nitrate concentration were 600 μmol/m 2 /s and 8.8 mM, respectively. The fed-batch cultivation strategy was shown to further improve lutein production. The highest lutein productivity (3.56 ± 0.10 mg/L/d) and content (5.05 ± 0.20 mg/g) were obtained when pulse-feeding of 2.2 mM nitrate was employed. This study demonstrated the potential of using Desmodesmus sp. F51 as a lutein producer in practical applications. [ABSTRACT FROM AUTHOR]

Abstract: Microalgae biotechnology provides a new industrial paradigm that simultaneously yields various vital products and captures CO2 in a single process. Development of optimal strategies to harness microalgal resources is critical to full-scale production and application of microalgae-derived products. This work parametrically investigated the autotrophic cultivation of Spirulina platensis for enhanced simultaneous CO2 fixation and phycocyanin production using conical flasks and newly designed photobioreactors. In the absence of culture aeration in the conical flasks, a maximum biomass concentration of 3.20g/L was achieved under alkaline conditions with initial pH of ∼9. In the presence of culture aeration, a maximum biomass concentration of 5.96g/L was obtained under intermittent CO2 supply at 20mM/(L2d) (that is 20mM/L every other day). Continuous sparging of 0.1L/min compressed air in combination with 20mM/(Ld) intermittent CO2 supply into a customarily designed photobioreactor resulted in biomass and crude phycocyanin concentrations of 5.92g/L and 1.06g/L respectively. Further photobioreaction optimization resulted in biomass and phycocyanin concentrations of 7.27g/L and 1.22g/L respectively using 20mM/Ld CO2 intermittent aeration supplemented with continuously supplied compressed air under specific flow conditions. The highest volumetric titre of phycocyanin obtained in this work is amongst the highest reported in literature. These results indicate that high biomass, phycocyanin concentration and CO2 fixation rate could be obtained with minimal extra effort simply by optimizing bioprocess conditions. The growth results of S. platensis cultivation fitted well to the logistic rate equation. [Copyright &y& Elsevier]