Improved production of poly-γ-glutamic acid with low molecular weight under high ferric ion concentration stress in Bacillus licheniformis ATCC 9945a

Abstract This study found that high ferric ion (Fe 3+ ) concentrations lead to high poly-γ-glutamic acid (γ-PGA) production and low-molecular-weight γ-PGA. In cultures containing 7.4 mmol/L FeCl 3 , the average molecular weight of γ-PGA reached 3.18 ± 0.3 × 10 5  Da, which is a 76% decrease from that in the culture without FeCl 3 (1.31 ± 0.14 × 10 6  Da). Cultures containing increasing concentrations of FeCl 3 (0–7.4 mmol/L) showed a corresponding increase in γ-PGA yield from 26.57 ± 1.64 to 34.93 ± 1.05 g/L. Transcription level analysis indicated that high FeCl 3 concentrations could enhance the expression of γ-PGA synthetase genes ( pgsA , pgsB, and pgsC ), which may contribute to the improved production of γ-PGA. In addition, γ-PGA degradation genes ggt (encoding γ-glutamyltransferase) and cwlO were found to contribute to a lower γ-PGA molecular weight in cultures containing 7.4 mmol/L FeCl 3 . The result of γ-glutamyltransferase activity was in agreement with the results of the transcription level analysis. Overall, this study would provide a novel method for the regulation of synthesis of γ-PGA with low molecular weight.