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

Abstract

Due to the promising applications, the demand to enhance poly-γ-glutamic acid (γ-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 γ-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 γ-PGA fermentation, which obtained a final concentration of 6.56 ± 0.27g/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 γ-PGA from lignocellulosic biomass and circumvent excessive non-food usage of glucose.