BackgroundSchizochytrium limacinum SR21 is a potential industrial strain for docosahexaenoic acid (DHA) production that contains more than 30–40 % DHA among its total fatty acids.MethodsTo resolve the DHA biosynthesis mechanism and improve DHA production at a systematic level, a genomescale metabolic model (GSMM), named iCY1170_DHA, which contains 1769 reactions, 1659 metabolites, and 1170 genes, was reconstructed.ResultsBased on genome annotation results and literature reports, a new DHA synthesis pathway based on a polyketide synthase (PKS) system was detected in S. limacinum. Similarly to conventional fatty acid synthesis, the biosynthesis of DHA via PKS requires abundant acetyl-CoA and NADPH. The in silico addition of malate and citrate led to increases of 24.5 % and 37.1 % in DHA production, respectively. Moreover, based on the results predicted by the model, six amino acids were shown to improve DHA production by experiment. Finally, 30 genes were identified as potential targets for DHA over-production using a Minimization of Metabolic Adjustment algorithm.ConclusionsThe reconstructed GSMM, iCY1170_DHA, could be used to elucidate the mechanism by which DHA is synthesized in S. limacinum and predict the requirements of abundant acetyl-CoA and NADPH for DHA production as well as the enhanced yields achieved via supplementation with six amino acids, malate, and citrate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2042-y) contains supplementary material, which is available to authorized users.

Chitosanase (EC3.2.1.132) can be used to selectively produce partially acetylated chitosan oligosaccharides (COSs), which are functional biopolymers that can widely be utilized as environmentally friendly agents, due to their bioactive, nontoxic, nonallergenic, and biodegradable properties. Different chitosanases can give rise to hydrolysates with diverse functions, making the development of novel chitosanases of great importance in applied biotechnologies. Here, we successfully expressed a novel chitosanase derived from Aspergillus fumigatus CJ22-326 in Pichia pastoris GS115, which could controllably produce chitosan oligosaccharides with desirable polymeric degrees. After glycosylation, the sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the recombinant enzyme Csn75 showed two specific protein bands with sizes of 25.5 and 23.5 kDa individually. The activity of the glycosylated Csn75 was 3.6-fold of that of the deglycosylated Csn75, indicating that glycosylation can greatly increase the activity. K m and V max values of the purified Csn75 were 0.46 mg/mL and 6.03 μmol·mL–1·min–1 separately, revealing a good affinity and high catalytic efficiency to the substrate. Moreover, biochemical tests confirmed that Csn75 had the highest activity from 55 to 65 °C when pH ranged from 5.0 to 6.0 and exhibited 4-fold activity in the presence of 1 mM Mn2+. Interestingly, the hydrolysis rate of the crude Csn75 (30 U/mL) can reach up to 90.65% in 4 h when using 2% chitosan as the substrate, producing a mixture of COS with desirable degrees of polymerization (DP), which significantly inhibited the mycelium growth of phytopathogenic fungi. This study proved Csn75 to be a promising chitosanase for the preparation of desirable chitosan oligosaccharides that are green biocides applicable for sustainable agricultural production and environmental protection.

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Human NUDC (hNUDC) was initially characterized as a nuclear migration protein based on the similarity of its C-terminus to that of fungal NUDC from Aspergillus nidulans. However, hNUDC is a 331 amino acid protein whereas fungal NUDC is 198 amino acids in length. The extra N-terminal portion of hNUDC has no known function or homology to other proteins. In this study, we report the binding of hNUDC to the extracellular domain of the thrombopoietin receptor (Mpl) as detected by the yeast two-hybrid system, GST pull-down, and co-immunoprecipitation. Our deletion analysis demonstrated that amino acids between positions 100 and 238 as the critical domain mediating the hNUDC and Mpl interactions as detected by the two-hybrid system and GST pull-down assay. Immunofluorescence staining of human megakaryocyte cells indicated that hNUDC and Mpl colocalized at all stages of megakaryocyte development. Substantial colocalization of hNUDC with microtubules was also detected around nuclei and elongated microtubular structures, especially in proplatelet extensions.

The mutant strain designated as ART18, obtained from the wild-type strain Clostridium acetobutylicum PW12 treated by atmospheric and room temperature plasma, showed higher solvent tolerance and butanol production than that of the wild-type strain. The production of butanol was 11.3 ± 0.5 g/L, 31 % higher than that of the wild-type strain when it was used for acetone, butanol, and ethanol fermentation in P2 medium. Furthermore, the effects of cassava flour concentration, pH regulators, and vitamins on the ABE production were also investigated. The highest butanol production of 15.8 ± 0.8 g/L and butanol yield (0.31 g/g) were achieved after the above factors were optimized. When acetone, butanol, and ethanol fermentation by ART18 was carried out in a 15-L bioreactor, the butanol production, the productivity of butanol, and the total solvent were 16.3 ± 0.9, 0.19, and 0.28 g/L(/)h, respectively. These results indicate that ART18 is a promising industrial producer in ABE fermentation.

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Butanol from renewable biomass is a promising advanced biofuel that can be used as an optimal substitute for gasoline in the transportation sectors, and therefore, large-scale industrial production of biobutanol has great importance to the development of sustainable energy. However, the low bioproductivity of butanol is a big challenge, despite great progress in metabolic engineering and bioprocessing. More importantly, butanol biosynthesis is mainly a consequence of anaerobic transformations catalyzed by specific oxidoreductases and driven by the reducing power; thus, both redox metabolism and electron transfer determine the efficiency of butanol bioconversion. In this Perspective, we highlight the significance of redox balance and electron transfer or energy conversion as a foundation to propose a strategy toward high butanol production from biocatalysis to bioelectrocatalysis. Potential challenges and future directions in the upcoming years are discussed from a bioelectrochemical perspective.

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