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Highlights • Fermentation kinetics of DHA production using Schizochytrium sp. was developed. • Growth-uncoupled DHA production by Schizochytrium sp. was studied. • Multi-stage continuous fermentation prediction model was established and applied. • The DHA efficient production was realized by multi-stage continuous fermentation. Abstract Docosahexaenoic acid (DHA) has wide-ranging benefits for normal development of the visual and nervous systems in infants. A sustainable source of DHA production through fermentation using Schizochytrium sp. has been developed. In this paper, we present the discovery of growth-uncoupled DHA production by Schizochytrium sp. and the development of corresponding kinetic models of fed-batch fermentations, which can be used to describe and predict the cell growth and substrate utilization as well as lipid and DHA production. Based on this kinetic model, a predictive model of multi-stage continuous fermentation process was established and used to analyze, optimize and design the process parameters. Optimal predicted processes of two-stage and three-stage continuous fermentation were developed and verified in lab-scale bioreactor based on the predicted process parameters. A successful three-stage continuous fermentation was achieved, which increased the lipid, DHA content and DHA productivity by 47.6, 64.3 and 97.1%, respectively, compared with two-stage continuous fermentation. [ABSTRACT FROM AUTHOR]

Process scale-up is a critical factor for realizing the industrial-scale production of docosahexaenoic acid (DHA). To improve the efficiency of scale-up, a strategy based on computational fluid dynamics analysis and investigation of microbial physiological properties was developed. We first investigated the physiological response of Schizochytrium sp. to different scale bioreactors, and the results indicated that a homogeneous culture environment was beneficial for cell growth and DHA biosynthesis. Fluid dynamics of different scale bioreactors were further investigated and impeller combinations were designed and optimized by computational methods to obtain a homogeneous culture environmental in a 7000 L bioreactor. The results showed that the optimal impeller combination could provide a more balanced culture environment, similar to lab-scale bioreactors. When the optimal strategy was used to scale-up the DHA fermentation, the biomass, DHA concentration, DHA percentage in biomass and DHA productivity reached 128.3 g/L, 39.2 g/L, 30.5%, 326.5 mg/(L h), respectively. This study thus introduces a highly efficient and economical scale-up strategy for DHA production using Schizochytrium sp. [ABSTRACT FROM AUTHOR]

Omega-3 fatty acids have received considerable attention due to their substantial health benefits. The aim of this study was to investigate the roles of acyltransferase (AT) domain and replace it for regulating fatty acid profile in Schizochytrium sp.. Herein, Schizochytrium sp. was engineered via gene deletion of AT and replacement of the native AT with its homologue, Shew-AT domain from Shewanella sp.. The docosahexaenoic acid (DHA) content in total fatty acids of the AT deficient strain observably decreased from 49.52% to 35.2% and the strain exhibited a low growth rate. Replacement with the Shew-AT gene recovered the cell growth and led to a high DHA content, with 3.7 times more eicosapentaenoic acid (EPA). This study will expand knowledge for synthesis of polyunsaturated fatty acid and facilitate the design of microbes with high yields of omega-3 fatty acids as a source of these valuable compounds for nutritional improvement. [ABSTRACT FROM AUTHOR]

Oxygen uptake rate (OUR) and respiratory quotient (RQ) are key respiratory parameters for docosahexaenoic acid (DHA) production by Schizochytrium sp. HX-308 under dissolved oxygen limited conditions. To investigate the relationship of OUR and RQ with culture status, three independent cultures with different aeration rates were performed in a 50 L bioreactor. OUR was found to be positively correlated with the aeration rate, which reflected the oxygen supply level in each culture. The highest biomass, reaching 124.5 g/L, was achieved under the highest OUR. DHA content was found to be highly correlated with the RQ value, and the highest DHA content (44.85% in total fatty acids, w/w) was achieved in the highest RQ level, which implies that the polyketide synthase pathway was more active. OUR and RQ, which reflect the physiological state of microorganisms, are suggested as synergistic real-time bioprocess monitoring parameters for DHA fermentation. [ABSTRACT FROM AUTHOR]

Different fermentation processes, including batch, fed-batch and repeated fed-batch processes by Schizochytrium sp., were studied and compared for the effective DHA-rich microbial lipids production. The comparison between different fermentation processes showed that fed-batch process was a more efficient cultivation strategy than the batch process. Among the four different feeding strategies, the glucose concentration feed-back feeding strategy had achieved the highest fermentation results of final cell dry weight, total lipids content, DHA content and DHA productivity of 72.37, 48.86, 18.38 g l −1 and 138.8 mg l −1 h −1, respectively. The repeated fed-batch process had the advantages of reducing the time and cost for seed culture and inoculation between each fermentation cycles. The results of fermentation characteristics and lipid characterization of the repeated fed-batch process indicated that this repeated fed-batch process had promising industrialization prospect for the production of DHA-rich microbial lipids. [ABSTRACT FROM AUTHOR]

Background: Schizochytrium sp. is a marine microalga with great potential as a promising sustainable source of lipids rich in docosahexaenoic acid (DHA). This organism’s lipid accumulation machinery can be induced by various stress conditions, but this stress induction usually comes at the expense of lower biomass in industrial fermentations. Moreover, oxidative damage induced by various environmental stresses can result in the peroxidation of lipids, and especially polyunsaturated fatty acids, which causes unstable DHA production, but is often ignored in fermentation processes. Therefore, it is urgent to develop new production strains that not only have a high DHA production capacity, but also possess strong antioxidant defenses. Results: Adaptive laboratory evolution (ALE) is an effective method for the development of beneficial phenotypes in industrial microorganisms. Here, a novel cooperative two-factor ALE strategy based on concomitant low temperature and high salinity was applied to improve the production capacity of Schizochytrium sp. Low-temperature conditions were used to improve the DHA content, and high salinity was applied to stimulate lipid accumulation and enhance the antioxidative defense systems of Schizochytrium sp. After 30 adaptation cycles, a maximal cell dry weight of 126.4 g/L and DHA yield of 38.12 g/L were obtained in the endpoint strain ALE-TF30, which was 27.42 and 57.52% higher than parental strain, respectively. Moreover, the fact that ALE-TF30 had the lowest concentrations of reactive oxygen species and malondialdehyde among all strains indicated that lipid peroxidation was greatly suppressed by the evolutionary process. Accordingly, the ALE-TF30 strain exhibited an overall increase of gene expression levels of antioxidant enzymes and polyketide synthases compared to the parental strain. Conclusion: This study provides important clues on how to overcome the negative effects of lipid peroxidation on DHA production in Schizochytrium sp. Taken together, the cooperative two-factor ALE process can not only increase the accumulation of lipids rich in DHA, but also prevent the loss of produced lipid caused by lipid peroxidation. The strategy proposed here may provide a new and alternative direction for the industrial cultivation of oil-producing microalgae. [ABSTRACT FROM AUTHOR]

Oxygen-mediated cell damage is an important issue in aerobic fermentation. In order to counteract these problems, effect of ascorbic acid on cell growth and docosahexaenoic acid (DHA) production was investigated in Schizochytrium sp. Addition of 9 g/L ascorbic acid resulted in 16.16% and 30.44% improvement in cell dry weight (CDW) and DHA yield, respectively. Moreover, the total antioxidant capacity (T-AOC) of cells decreased from 2.17 at 12 h to 0 at 60 h and did not recover, while ascorbic acid addition could extend the time of arrival zero with the reduced intracellular ROS. However, ROS levels still increased after 72 h. Therefore, to further solve the problem of high ROS levels and low T-AOC of cells after 72 h, a two-point addition strategy was proposed. With this strategy, DHA yield was further increased to 38.26 g/L. This work innovatively investigated the feasibility of manipulating Schizochytrium sp. cultivation through ROS level and T-AOC. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation and mobilization of lipid fractions were investigated thoroughly. [•] Fatty acid combined on PLs could be changed more easily than NLs. [•] The shift of NL to PL and the increase of UMs happed in lipid turnover stage. [•] DHA enrichment in lipid turnover stage mainly happened in PLs. [•] A positive correlation exited between the synthesis of PUFA and UMs. [ABSTRACT FROM AUTHOR]

Highlights • Algae-residue from Schizochytrium sp. was used as nitrogen source to replace yeast extract. • Cane molasses was used as carbon source to substitute glucose. • Two-stage culture with different carbon sources increased the efficiency of DHA production. • This work offers a strategy to reduce waste by-products discharge and cut production costs. Abstract The aim of this work was to reduce the algae-residue emission and make use of cane molasses as fermentation materials for docosahexaenoic acid (DHA) fermentaion by Schizochytrium sp., which further could cut the cost of DHA production. Algae-residue and cane molasses were respectively used as nitrogen and carbon sources to replace yeast extract and glucose. A significant DHA yield of 18.58 g/L was obtained using algae-residue, while cane molasses could not be used well as sole carbon source due to the presence of undesirable substance. A two-stage culture strategy with glucose followed by pretreated cane molasses as carbon source was developed, resulting in a final DHA yield of 15.22 g/L. This study therefore offers an economical and green strategy for DHA production by Schizochytrium sp. [ABSTRACT FROM AUTHOR]

Lipid accumulation of Schizochytrium sp. can be induced by stress condition, but this stress-induction usually reduce cell growth and cause oxidative damage, which can eventually lower the lipid yield. Here, adaptive laboratory evolution (ALE) combined high salinity was performed to enhance the antioxidant system and lipid accumulation. The final strain ALE150, which was obtained after 150 days, showed a maximal cell dry weight (CDW) of 134.5 g/L and lipid yield of 80.14 g/L, representing a 32.7 and 53.31% increase over the starting strain, respectively. Moreover, ALE150 exhibited an overall higher total antioxidant capacity (T-AOC) and lower reactive oxygen species (ROS) levels than the starting strain. Furthermore, the regulatory mechanisms responsible for the improved performance of ALE150 were analyzed by transcriptomic analysis. Genes related to the antioxidant enzymes and central carbon metabolism were up-regulation. Moreover, the metabolic fluxes towards the fatty acid synthase (FAS) and polyketide synthase (PKS) pathways were also changed. [ABSTRACT FROM AUTHOR]

Fermentation wastewater (FW) and algal residue are major by-products of docosahexaenoic acid (DHA) fermentations utilizing Schizochytrium sp. In order to reduce production costs and environmental pollution, we explored the application of FW and algal-residue extract (AE) for DHA production. Components analysis showed that FW and AE contained some mineral elements and protein residues, respectively. When they were used for DHA fermentation, results showed that 20% replacement of fresh water by FW and 80% replacement of yeast extract nitrogen by AE reached DHA content of 22.23 g/L and 27.10 g/L, respectively. Furthermore, a novel medium that utilizes a mixture of FW and AE was applied for DHA fermentation, whereby the final DHA yield reached 28.45 g/L, 24.56% higher than conventional medium. The strategy of valorizing fermentation waste provides a new method for reducing the costs and reducing environmental pollution of microbial fermentations. [ABSTRACT FROM AUTHOR]