A new strategy for enhancement of poly-γ-glutamic acid production by multiple physicochemical stresses inBacillus licheniformis

BACKGROUND The 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-γ-glutamic acid (γ-PGA) production. RESULTS The effects of multiple physicochemical stresses on the production and synthetase genes transcription of γ-PGA were investigated in Bacillus licheniformis WX-02. Under heat stress stimulated at 50 °C, osmotic stress induced by 3% KCl, and alkaline stress mediated by pH 8.5, γ-PGA yields increased by 66%, 106% and 133%, respectively, and the transcription levels of γ-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 γ-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 γ-PGA yield reached 29.34 g L−1, 185% higher than the control. CONCLUSION This study provided a novel strategy to enhance γ-PGA yield by physicochemical stresses treatment, and the possible mechanism was also determined. The stress-mediated strategy can be easily applied in γ-PGA production at large scale. © 2014 Society of Chemical Industry