Conversion of agroindustrial residues for high poly(?-glutamic acid) production by Bacillus subtilis NX-2 via solid-state fermentation
Bao Tang, Hong Xu, Zongqi Xu, Cen Xu, Zheng Xu, Peng Lei, Yibin Qiu, Jinfeng Liang, Xiaohai Feng
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing, 211816, China
Poly(γ-glutamic acid) (γ-PGA) production by Bacillus subtilis NX-2 was carried out through solid-state fermentation with dry mushroom residues (DMR) and monosodium glutamate production residues (MGPR; a substitute of glutamate) for the first time. Dry shiitake mushroom residue (DSMR) was found to be the most suitable solid substrate among these DMRs; the optimal DSMR-to-MGPR ratio was optimized as 12:8. To increase γ-PGA production, industrial waste glycerol was added as a carbon source supplement to the solid-state medium. As a result, γ-PGA production increased by 34.8%. The batch fermentation obtained an outcome of 115.6 g kg−1 γ-PGA and 39.5 ×108 colony forming units g−1 cells. Furthermore, a satisfactory yield of 107.7 g kg−1 γ-PGA was achieved by compost experiment on a scale of 50 kg in open air, indicating that economically large-scale γ-PGA production was feasible. Therefore, this study provided a novel method to produce γ-PGA from abundant and low-cost agroindustrial residues.
Keywords: Bacillus subtilis NX-2; Poly(?-glutamic acid); Solid-state fermentation; Agroindustrial residues