Production of poly-γ-glutamic acid (γ-PGA) from xylose-glucose mixtures by Bacillus amyloliquefaciens C1

Due to the promising applications, the demand to enhance poly-gamma -glutamic acid (gamma -PGA) production while decreasing the cost has increased in the past decade. Here, xylose/glucose mixture and corncob hydrolysate (CCH) was evaluated as alternatives for gamma -PGA production by Bacillus amyloliquefaciens C1. Although both have been validated to support cell growth, glucose and xylose were not simutaneously consumed and exhibited a diauxic growth pattern due to carbon catabolite repression (CCR) in B. amyloliquefaciens C1, while the enhanced transcription of araE alleviated the xylose transport bottleneck across a cellular membrane. Additionally, the xyl operon (xylA and xylB), which was responsible for xylose metabolism, was strongly induced by xylose at the transcriptional level. When cultured in a mixed medium, xylR was sharply induced to 3.39-folds during the first 8-h while reduced to the base level similar to that in xylose medium. Finally, pre-treated CCH mainly contained a mixture of glucose and xylose was employed for gamma -PGA fermentation, which obtained a final concentration of 6.56 +/- 0.27 g/L. Although the glucose utilization rate (84.91 +/- 1.81%) was lower than that with chemical substrates, the xylose utilization rate (43.41 +/- 2.14%) and the sodium glutamate conversion rate (77.22%) of CCH were acceptable. Our study provided a promising approach for the green production of gamma -PGA from lignocellulosic biomass and circumvent excessive non-food usage of glucose.

Automated summary

The study evaluated xylose/glucose mixture and corncob hydrolysate as alternatives for gamma-PGA production, finding a diauxic growth pattern of glucose and xylose in B. amyloliquefaciens C1, with enhanced araE transcription alleviating the xylose transport bottleneck. When cultured in a mixed medium, xylR expression was sharply induced, ultimately achieving green production of gamma-PGA from lignocellulosic biomass.