The probiotic of Bacillus subtilis ( B.subtilis ) is widely used in animal husbandry as a promising alternative to antibiotics, and a high value-added bioproduct from abundant and low-cost agricultural straws. For efficient fermentation of xylose-rich corncob slurry to B. subtilis cells, the step-by-step fermentation process (SSFP) and one-step fermentation process (OSFP) were proposed and compared by the combined technology of sulfuric acid pretreatment and enzymatic hydrolysis with cellulase . Xylose and glucose were fermented separately and sequentially in the SSFP route, while they were co-fermented in OSFP route. Here, B. subtilis performed an efficient bioconversion and almost fermented simultaneously glucose, xylose and arabinose in corncob slurry. We could obtain 326.8 g of B. subtilis in SSFP and 323.7 g probiotic cells in OSFP from 1000 g of corncob, respectively. In general, the OSFP route was preferable by virtue of a straightforward process and simple operation.
Yang Fengyu,Xu Jiayu,Zhu Yichun,Wang Yi,Xu Meijuan,Rao Zhiming
Background Agmatine is a member of biogenic amines and is an important medicine which is widely used to regulate body balance and neuroprotective effects. At present, the industrial production of agmatine mainly depends on the chemical method, but it is often accompanied by problems including cumbersome processes, harsh reaction conditions, toxic substances production and heavy environmental pollution. Therefore, to tackle the above issues, arginine decarboxylase was overexpressed heterologously and rationally designed in Corynebacterium crenatum to produce agmatine from glucose by one-step fermentation.Results In this study, we report the development in the Generally Regarded as Safe (GRAS) l-arginine-overproducing C. crenatum for high-titer agmatine biosynthesis through overexpressing arginine decarboxylase based on metabolic engineering. Then, arginine decarboxylase was mutated to release feedback inhibition and improve catalytic activity. Subsequently, the specific enzyme activity and half-inhibitory concentration of I534D mutant were increased 35.7% and 48.1%, respectively. The agmatine production of the whole-cell bioconversion with AGM3 was increased by 19.3% than the AGM2. Finally, 45.26 g/L agmatine with the yield of 0.31 g/g glucose was achieved by one-step fermentation of the engineered C. crenatum with overexpression of speAI534D.Conclusion sThe engineered C. crenatum strain AGM3 in this work was proved as an efficient microbial cell factory for the industrial fermentative production of agmatine. Based on the insights from this work, further producing other valuable biochemicals derived from l-arginine by Corynebacterium crenatum is feasible.
Jiawei Li,Ru Song,Xiaoyu Zou,Rongbian Wei,Jiaxing Wang
One-step fermentation, inoculated withLactobacillus fermentum(L. fermentum) in shrimp by-products, was carried out to obtain chitin and flavor protein hydrolysates at the same time. The fermentation conditions were optimized using response surface methodology, resulting in chitin with a demineralization rate of 89.48%, a deproteinization rate of 85.11%, and a chitin yield of 16.3%. The surface of chitin after fermentation was shown to be not dense, and there were a lot of pores. According to Fourier transform infrared spectroscopy and X-ray diffraction patterns, the fermented chitin belonged to α-chitin. More than 60 volatiles were identified from the fermentation broth after chitin extraction using gas chromatography–ion transfer spectrometry analysis.L. fermentumfermentation decreased the intensities of volatile compounds related to unsaturated fatty acid oxidation or amino acid deamination. By contrast, much more pleasant flavors related to fruity and roasted aroma were all enhanced in the fermentation broth. Our results suggest an efficient one-step fermentation technique to recover chitin and to increase aroma and flavor constituents from shrimp by-products.Keywords:shrimp by-products;L. fermuntum;one-step fermentation;chitin;flavor volatiles;gas chromatography–ion transfer spectrometry
危险品化学品经营许可证（带存储）