Nonsterilized fermentative production of poly--glutamic acid from cassava starch and corn steep powder by a thermophilic Bacillus subtilis

BACKGROUNDPoly--glutamic acid (-PGA) is a homopolymer obtained by microbial fermentation, which has wide potential applications in many fields. However, costs of raw materials and the fermentation process are still a limiting factor in the commercial-scale production of -PGA. Thus, it is necessary to continue to optimize its production by developing a cost-effective fermentation process. RESULTSBacillussubtilis GXC-36 was proven to be able to produce -PGA efficiently by nonsterilized fermentation. The yield of -PGA reached 36.380.81gL(-1) with a high productivity of 1.65gL(-1)h(-1) by nonsterilized batch fermentation in a 10L fermenter using glucose and yeast extract (YE) as carbon and nitrogen source. Furthermore, B.subtilis GXC-36 could produce -PGA efficiently using cassava starch (CS) and corn steep powder (CSP) instead of glucose and YE for -PGA production, and the yield of -PGA also reached 33.51 +/- 0.72gL(-1) with productivity of 1.52gL(-1)h(-1) in a 10L fermenter. Fermentative benefits evaluation indicated that the fermentation cost of nonsterilized fermentation using CS and CSP was only 60.6% of sterilized fermentation using glucose and YE. CONCLUSIONThis study provides an economical and simple process for -PGA production by nonsterilized fermentation with low-cost raw materials. (c) 2018 Society of Chemical Industry