Manyu Tang,Xin Zhen,Guoqiang Zhao,Shuang Wu,Wei Hua,Jingwen Qiang,Cheng Yanling,Wanqing Wang
The purple nonsulfur bacteria, Rhodospirillum rubrum , is recognized as a potential strain for PHAs bioindustrial processes since they can assimilate a broad range of carbon sources, such as syngas, to allow reduction of the production costs. In this study, we comparatively analyzed the biomass and PHA formation behaviors of R . rubrum under 100% CO and 50% CO gas atmosphere and found that pure CO promoted the PHA synthesis (PHA content up to 23.3% of the CDW). Hydrogen addition facilitated the uptake and utilization rates of CO and elevated 3-HV monomers content (molar proportion of 3-HV up to 9.2% in the presence of 50% H 2 ). To elucidate the genetic events culminating in the CO assimilation process, we performed whole transcriptome analysis of R . rubrum grown under 100% CO or 50% CO using RNA sequencing. Transcriptomic analysis indicated different CO 2 assimilation strategy was triggered by the presence of H 2 , where the CBB played a minor role. An increase in BCAA biosynthesis related gene abundance was observed under 50% CO condition. Furthermore, we detected the α-ketoglutarate (αKG) synthase, converting fumarate to αKG linked to the αKG-derived amino acids synthesis, and series of threonine-dependent isoleucine synthesis enzymes were significantly induced. Collectively, our results suggested that those amino acid synthesis pathways represented a key way for carbon assimilation and redox potential maintenance by R . rubrum growth under syngas condition, which could partly replace the PHA production and affect its monomer composition in copolymers. Finally, a fed-batch fermentation of the R . rubrum in a 3-l bioreactor was carried out and proved H 2 addition indeed increased the PHA accumulation rate, yielding 20% ww -1 PHA production within six days.
Baoming Tian,Xue Zhou,Yan Geng,Jiangning Hu,Bangwei Ye,Peilong Sun,Kai Yang
Grifola frondosa is a highly valued, edible and biologically active fungus in which the polysaccharide component plays a major role. To investigate the fundamental structure, in vitro digestion and fermentation characteristics of Grifola frondosa polysaccharides (GFP), GFP from the waste residue of Grifola frondosa after water extraction was re-extracted by alkaline solution. The carbohydrate and β-glucan contents of GFP were 91.61% and 60.57%, respectively, and were mainly composed of glucose. GFP can form triple supercoils and combine with Congo red, and the surface of GFP was smooth and dense, and the particles were in the shape of long column, sheet and ellipse. Analysis of carbohydrate, reducing sugars, and further chromatogram data also showed that GFP was not degraded by the simulated digestion process of the mouth, stomach and small intestine. Fecal fermentation of GFP significantly increased the abundance of Bacteroidota, and decreased Proteobacterias in both normal weight and obese subjects in vitro . The short-chain fatty acid (SCFA)-producing bacteria, Faecalibacterium , Erysipelotrichaceae_UCG_003 , Lactococcus were increased, and Dorea and Escherichia-Shigella were reduced after GFP treatment. Thus, the molecular of GFP was utilized and degraded by the gut microbiota and metabolized into SCFAs. This decreased pH, H 2 S, and NH 3, as well as increased CO 2 in the fermentation broth. In conclusion, GFP can modulate the composition of the gut microbiota and is a potentially functional product.
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