Regulation of stereochemical composition of poly-γ-glutamic acids produced by Bacillus licheniformis within various Mn2+ concentration

Abstract:

[Objective] The mechanism of the generation of various kinds of poly-γ-glutamic acids (γ-PGA) from Bacillus licheniformis WBL-3 affected by Mn2+ was investigated in this study. [Methods] Three L- and D-glutamic metabolism related enzymes, glutamate racemase (GR; encoded by racE), D-alanine aminotransferase (D-DDT; encoded by dat) and glutamine synthetase (GS; encoded by gltA), were cloned and expressed meanwhile B. subtilis KH-2 was used as the control strain. The mechanism synthesis of γ-PGA by different concentration of Mn2+ was studied using the methods of enzyme activity, combined with transcriptional analysis. [Results] When the concentration of Mn2+ varied from 0 to 0.6 mmol/L, the proportion of D- isomer increased from 22% to 67%. The catalytic activity (kcat/Km) of GR in Bacillus licheniformis WBL-3 with 0.6 mmol/L Mn2+ is higher than that without Mn2+. The GS activity was measured only in the presence of Mn2+. RT-PCR study showed that the transcription ratio of racE, dat and gltA with 0.6 mmol/L Mn2+ to those without Mn2+ was 2.16, 4.44 and 1.84-fold, respectively. [Conclusion] Mn2+ activated the expression of GR, D-DDT and GS, promoted the metabolism of L-glutamic acid, increased the proportion of D-glutamic acid, and increased the proportion of γ-D-PGA.