Highly efficient rice straw utilization for poly-(γ-glutamic acid) production by Bacillus subtilis NX-2.

Lignocellulosic biomass has been identified as an economic and environmental feedstock for future biotechnological production. Here, for the first time, poly-(γ-glutamic acid) (PGA) production by Bacillus subtilis NX-2 using rice straw is investigated. Based on two-stage hydrolysis and characteristic consumption of xylose and glucose by B. subtilis NX-2, a co-fermentation strategy was designed to better accumulate PGA in a 7.5L fermentor by two feeding methods. The maximum cumulative respective PGA production and PGA productivity were 73.0 ± 0.5 g L(-1) and 0.81 g L(-1) h(-1) by the continuous feeding method, with carbon source cost was saved by 84.2% and 42.5% compared with glucose and cane molasse, respectively. These results suggest that rice straw, a type of abundant, low-cost, non-food lignocellulosic feedstock, may be feasibly and efficiently utilized for industrial-scale production of PGA.

Economic process to co-produce poly(ε-l-lysine) and poly(l-diaminopropionic acid) by a pH and dissolved oxygen control strategy.

This study tended to apply biorefinery of indigenous microbes to the fermentation of target-product generation through a novel control strategy. A novel strategy for co-producing two valuable homopoly(amino acid)s, poly(ε-l-lysine) (ε-PL) and poly(l-diaminopropionic acid) (PDAP), was developed by controlling pH and dissolved oxygen concentrations in Streptomyces albulus PD-1 fermentation. The production of ε-PL and PDAP got 29.4 and 9.6gL(-1), respectively, via fed-batch cultivation in a 5L bioreactor. What is more, the highest production yield (21.8%) of similar production systems was achieved by using this novel strategy. To consider the economic-feasibility, large-scale production in a 1t fermentor was also implemented, which would increase the gross profit of 54,243.5USD from one fed-batch bioprocess. This type of fermentation, which produces multiple commercial products from a unified process is attractive, because it will improve the utilization rate of raw materials, enhance production value and enrich product variety.

Conversion of agroindustrial residues for high poly(γ-glutamic acid) production by Bacillus subtilis NX-2 via solid-state fermentation.

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 39.5×10(8) 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.