Alanine mother liquor as a nitrogen source for docosahexaenoic acid production by Schizochytrium sp. B4D1

Production of polyunsaturated fatty acids by Schizochytrium (Aurantiochytrium) spp

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed.

Novel Mode Engineering for β-Alanine Production in Escherichia coli with the Guide of Adaptive Laboratory Evolution

The strategy of anaerobic biosynthesis of β-alanine by Escherichia coli (E. coli) has been reported. However, the low energy production under anaerobic condition limited cell growth and then affected the production efficiency of β-alanine. Here, the adaptive laboratory evolution was carried out to improve energy production of E. coli lacking phosphoenolpyruvate carboxylase under anaerobic condition. Five mutants were isolated and analyzed. Sequence analysis showed that most of the consistent genetic mutations among the mutants were related with pyruvate accumulation, indicating that pyruvate accumulation enabled the growth of the lethal parent. It is possible that the accumulated pyruvate provides sufficient precursors for energy generation and CO₂ fixing reaction catalyzed by phosphoenolpyruvate carboxykinase. B0016-100BB (B0016-090BB, recE::FRT, mhpF::FRT, ykgF::FRT, mhpB:: mhpB *, mhpD:: mhpD *, rcsA:: rcsA *) was engineered based on the analysis of the genetic mutations among the mutants for the biosynthesis of β-alanine. Along with the recruitment of glycerol as the sole carbon source, 1.07 g/L β-alanine was generated by B0016-200BB (B0016-100BB, aspA::FRT) harboring pET24a-panD-AspDH, which was used for overexpression of two key enzymes in β-alanine fermentation process. Compared with the starting strain, which can hardly generate β-alanine under anaerobic condition, the production efficiency of β-alanine of the engineered cell factory was significantly improved.

The strategies to reduce cost and improve productivity in DHA production by Aurantiochytrium sp.: from biochemical to genetic respects

The marine oleaginous protist Aurantiochytrium sp. (Schizochytrium sp.) is a well-known docosahexaenoic acid (DHA) producer and its different DHA products are the ideal substitute for the traditional fish oil resource. However, the cost of the DHA products derived from Aurantiochytrium sp. (Schizochytrium sp.) is still high, limiting their wide applications. In order to reduce the cost or improve the productivity of DHA from the microbial resource, many researches are focusing on exploring the renewable and low-cost materials as feedbacks, and/or the stimulators for biomass and DHA production. In addition, the genetic engineering is also being used in the Aurantiochytrium sp. (Schizochytrium sp.) system for further improvement. These break the bottleneck of the DHA production by Aurantiochytrium sp. (Schizochytrium sp.) in some degree. In this review, the strategies used currently to reduce cost and improve DHA productivity, mainly from the utilizations of low-cost materials and effective stimulators to the genetic engineering perspectives, are summarized, and the availabilities from the cost perspective are also evaluated. This review provides an overview about the strategies to revolve the production cost and yield of the DHA by Aurantiochytrium sp. (Schizochytrium sp.), a theoretical basis for genetic modification of Aurantiochytrium sp. (Schizochytrium sp.), and a practical basis for the development of DHA industry. KEY POINTS : • Utilizations of various low-cost materials for DHA production • Inducing the growth and DHA biosynthesis by the effective stimulators • Reducing cost and improving DHA productivity by genetic modification • The availability from cost perspective is evaluated.

Use of Biofuel Industry Wastes as Alternative Nutrient Sources for DHA-Yielding Schizochytrium limacinum Production

The simultaneous use of crude glycerol and effluent from anaerobic digestate, both wastes derived from the biofuel industry, were tested in the frame of circular economy concept, as potential low-cost nutrient sources for the cultivation of rich in docosahexaenoic acid (DHA) oil microalgae strain Schizochytrium limacinum SR21. Initially, the optimal carbon and nitrogen concentration levels for high S. limacinum biomass and lipids production were determined, in a culture media containing conventional, high cost, organic nitrogen sources (yeast extract and peptone), micronutrients and crude glycerol at varying concentrations. Then, the effect of a culture media composed of crude glycerol (as carbon source) and effluent digestate at varying proportions on biomass productivity, lipid accumulation, proximate composition, carbon assimilation and fatty acid content were determined. It was shown that the biomass and total lipid content increased considerably with varying effluent concentrations reaching 49.2 g L−1 at 48% (v/v) of effluent concentration, while the lipid yield at the same effluent concentration reached 10.15 g L−1, compared to 17.0 g L−1 dry biomass and 10.2 g L−1 lipid yield when yeast extract and peptone medium with micronutrients was used. Compared to the control treatment, the above production was obtained with 48% less inorganic salts, which are needed for the preparation of the artificial sea water. It was shown that Schizochytrium limacinum SR21 was able to remediate 40% of the total organic carbon content of the biofuel wastes, while DHA productivity remained at low levels with saturated fatty acids comprising the main fraction of total fatty acid content. The results of the present study suggest that the simultaneous use of two waste streams from the biofuel industry can serve as potential nutrient sources for the growth of Schizochytrium limacinum SR21, replacing the high cost organic nutrients and up to one half the required artificial sea water salts, but upregulation of DHA productivity through optimization of the abiotic environment is necessary for industrial application, including aqua feed production.

Effect of sequential recycling of spent media wastewater on docosahexaenoic acid production by newly isolated strain Aurantiochytrium sp. ICTFD5

The main aim of this work was the optimization of recycled spent media wastewater (SMW) concentration for high biomass production of Aurantiochytrium sp. ICTFD5. Further, optimization for growth patterns and lipid accumulation capacity with three subsequent recycling runs was also performed. The biomass production after 96 h fermentation for recycling with 50% SMW was; 21.3 ± 1.5, 19.1 ± 1.3, 19 ± 1.2, and 23 ± 1.2 g/L for the first, second, third recycle runs, and control respectively. All the recycle runs were carried out with the same media and cultivation conditions. Subsequent recycling affected lipid accumulation, and it was decreased by ~4 to 9% compared to the control. The compositional shift of fatty acids was observed with sequential recycle runs, changing more towards saturated fatty acids content, suggesting it to be a new potential source for biodiesel feedstock.

Nutrient recovery from tofu whey wastewater for the economical production of docosahexaenoic acid by Schizochytrium sp. S31

Docosahexaenoic acid plays a vital role in human health as it is essential for the proper function of the nervous system and for visual functions. To decrease the cost of docosahexaenoic acid production by Schizochytrium, the cost of the medium should be further decreased. In this study, the use of tofu whey wastewater to culture Schizochytrium sp. for docosahexaenoic acid production was tested, with the goal of reducing the medium cost. The results indicated that tofu whey wastewater presented a better culture performance with respect to biomass, lipid, and docosahexaenoic acid production compared with three traditional media. Through simple pH adjustment, the biomass and docosahexaenoic acid productivity reached 1.89 and 0.24 g/L/day, respectively, which were much higher than those obtained using traditional medium. The removal efficiency of chemical oxygen demand, total nitrogen, and total phosphorus reached 64.7, 66.0, and 59.3%, respectively. Due to the rich nutrients in tofu whey wastewater, the use of extra nitrogen source was avoided and the total medium cost for docosahexaenoic acid production in cultures using tofu whey wastewater was <1/3 of that of traditional media. This result indicated that tofu whey wastewater is an effective and economic basal medium for docosahexaenoic acid production by Schizochytrium sp.

Transcriptome Mechanism of Utilizing Corn Steep Liquor as the Sole Nitrogen Resource for Lipid and DHA Biosynthesis in Marine Oleaginous Protist Aurantiochytrium sp

In the current study, corn steep liquor (CSL) is evaluated as an ideal raw agro-material for efficient lipid and docosahexaenoic acid DHA production by Aurantiochytrium sp. Low CSL level in medium (nitrogen deficiency) stimulated the biosynthesis of lipids and DHA while inhibiting cellular growth. The transcriptomic profiles of the Aurantiochytrium sp. cells are analyzed and compared when cultured under high (H group), normal (N group), and low (L group) levels of CSL in the medium. The discriminated transcriptomic profiles from the three groups indicates that changes in CSL level in medium result in a global change in transcriptome of Aurantiochytrium sp. The overall de novo assembly of cDNA sequence data generated 61,163 unigenes, and 18,129 of them were annotated in at least one database. A total of 5105 differently expressed (DE) genes were found in the N group versus the H group, with 2218 downregulated and 2887 upregulated. A total of 3625 DE genes were found in the N group versus the L group, with 1904 downregulated and 1721 upregulated. The analysis and categorization of the DE genes indicates that the regulation mechanism of CSL involved in the perception and transduction of the limited nitrogen signal, the interactions between the transcription factors (TFs) and multiple downstream genes, and the variations in downstream genes and metabolites, in sequence, are illuminated for the first time in the current study.