Limiting nitrogen supply has been routinely used as the master regulator to direct lipid biosynthesis. However, this strategy does not work with nitrogen-rich substrates, such as Jerusalem artichoke (JA), a fructose-based biomass, while it is difficult to obtain a high carbon-to-nitrogen (C/N) molar ratio. In this study, an alternative strategy to promote lipid accumulation by the oleaginous yeast Trichosporon fermentans CICC 1368 was developed by limiting phosphorous supply, and this strategy was implemented with JA hydrolysate as substrate. We showed that lipid accumulation was directly correlated with the C/P ratio of the culture media for T. fermentans. The time course of cell growth and lipid production was analyzed in a media with an initial C/P ratio of 6342, and the cellular lipid content could reach up to 48.5% of dry biomass. Moreover, JA hydrolysates were used as substrate for microbial lipid accumulation, under high C/P molar ratio condition, lipid yield, lipid content, and lipid coefficient increased by 10, 30, and 34%, respectively. It showed that by limiting phosphorus, the conversion of sugar into lipids can be improved effectively. Limiting phosphorus provides a promising solution to the problem of microbial lipid production with nitrogen-rich natural materials.

A 45‐day feeding trial was carried out to investigate the effects of dietary selenium yeast (Se‐yeast) on the survival, growth performance, activities of digestive enzymes and antioxidant enzymes, and body composition of early juvenile Apostichopus japonicus. Five isoprotic (15.6%) and isolipic (1.5%) feeds with graded levels of Se‐yeast (0, 0.5, 1.0, 1.5 and 2.0 mg/kg) were formulated and randomly allocated to the early juvenile sea cucumbers (initial weight: 0.11 ± 0.01 g). The results showed that the weight gain rate (WGR) and relative visceral weight ratio (RVW) significantly increased as the Se‐yeast supplementation increased from 0 to 1.0 mg/kg, and then reached a plateau with further increase in Se‐yeast, while survival rate (SR) increased as the supplementation level of Se‐yeast increased, and the lipase and amylase activities first significantly increased as the Se‐yeast increased from 0 to 1.0 mg/kg, and then significantly decreased with the continuous supplementation of Se‐yeast. The antioxidant capacity and nonspecific immunity were significantly elevated by the moderate level (0.5 and 1.0 mg/kg) of Se‐yeast. Besides, the activities of immune‐related enzymes and transcription of antioxidation‐related genes were significantly elevated by the supplementation of Se‐yeast. However, malonaldehyde contents were significantly reduced in the treatments with 0.5 and 1.0 mg/kg Se‐yeast. The selenium content in the body wall of the sea cucumber showed a markedly increasing trend with increasing Se‐yeast supplementation levels. Results above indicated that a moderate level (0.5–1.0 mg/kg) of Se‐yeast enhanced the growth performance, digestive enzyme activities, antioxidant capacity and nonspecific immunity of early juvenile A. japonicus.

Sinorhizobium meliloti 320 is a vitamin B12 (VB12) high‐producing strain that has been isolated and identified in our previous study. Because the regulatory toolbox for S. meliloti is limited, we searched for new genetic components and identified the two xylose‐inducible promoters PA and PB based on a promoter‐probe vector with a green fluorescent protein (GFP) as reporter. Compared with the ParaA promoter from S. meliloti, both promoters exhibited higher induced expression and lower basal expression. Subsequently, the influence of glucose or sucrose on the expression of GFP driven by these three promoters was assayed. Glucose repressed all three promoters, and the expression of ParaA was the lowest in the presence of glucose. Although sucrose repressed the expression of PA by 35% and improved the expression of ParaA by 16%, the expression level of PA was the highest and was 13% higher than that of ParaA. Lastly, we overexpressed the hemA gene in the C4 pathway using the PA promoter in S. meliloti 320, and the VB12 production of the engineered strain increased by 11%. The VB12 production was further increased by 11% by adding 0.1% sodium succinate to the culture medium.