A new strategy for enhancement of poly-gamma-glutamic acid production by multiple physicochemical stresses in Bacillus licheniformis

BACKGROUNDThe physicochemical stress-induced bioprocess is an efficient strategy for enhancement of the production of microbial metabolites, but multiple physicochemical stresses have not applied in poly--glutamic acid (-PGA) production. RESULTSThe effects of multiple physicochemical stresses on the production and synthetase genes transcription of -PGA were investigated in Bacillus licheniformisWX-02. Under heat stress stimulated at 50 degrees C, osmotic stress induced by 3% KCl, and alkaline stress mediated by pH 8.5, -PGA yields increased by 66%, 106% and 133%, respectively, and the transcription levels of -PGA synthetase gene PgsC were improved 3.1-fold, 3.6-fold and 5.4-fold compared with the control. Heat and osmotic stress also induced the up-regulation of another -PGA synthetase gene of PgsB with 1.4-fold and 4.3-fold increase, respectively. By combined application of heat and pH stress, the maximum -PGA yield reached 29.34gL(-1), 185% higher than the control. CONCLUSIONThis study provided a novel strategy to enhance -PGA yield by physicochemical stresses treatment, and the possible mechanism was also determined. The stress-mediated strategy can be easily applied in -PGA production at large scale. (c) 2014 Society of Chemical Industry