Microbial community structure and interactions between Aspergillus oryzae and bacteria in traditional solid-state fermentation of Jiangqu.

Microbial interactions play an important role in the formation, stabilization and functional performance of natural microbial communities. However, little is known about how the microbes present interactions to build a stable natural microbial community. Here, we developed Jiangqu, the solid-state fermented starters of thick broad-bean sauce formed naturally in factory, as model microbial communities by characterizing its diversity of microbial communities and batch stability. The dominant microbial strains and their fungi-bacteria interactions during solid-state fermentation of Jiangqu were characterized. In all batches of Jiangqu, Aspergillus oryzae, Bacillus, Staphylococcus and Weissella dominated in the communities and such a community structure could almost reduplicate between batches. Direct adsorption and competition were identified as the main interactions between A. oryzae and dominant bacteria during solid-state fermentation, which were quite different from liquid co-cultivation of A. oryzae and dominant bacteria. These results will help us better understand the intrinsic mechanism in the formation and stabilization of microbial communities from traditional solid-state qu-making and fermentation.

Efficient production of l-menthyl α-glucopyranoside from l-menthol via whole-cell biotransformation using recombinant Escherichia coli.

l-Menthyl α-D-glucopyranoside (α-MenG) is a glycoside derivative of l-menthol with improved water-solubility and new flavor property as a food additive. α-MenG can be synthesized through biotransformation, but its scale-up production was rarely reported. In this study, the properties of an α-glucosidase from Xanthomonas campestris pv. campestris 8004 (Agl-2) in catalyzing the glucosylation of menthol was investigated. Agl-2 can almost completely glycosylate l-menthol (> 99%) when using 1.2 M maltose as glycosyl donor. Accumulated glucose resulted from maltose hydrolysis and transglycosylation caused the inhibition of the glucosylation rate (40% reduction of the glucosylation rate in the presence of 1.2 M glucose) which can be avoided through whole-cell catalysis with recombinant E. coli. Interestingly, in spite of the poor solubility of menthol, the productivity of α-MenG reached 24.7 g/(L·h) in a 2 L catalyzing system, indicating industrialization of the reported approach.