Expression of the pgsB Encoding the Poly-gamma-DL-glutamate Synthetase of Bacillus subtilis (natto)

Abstract

An industrial strain of Bacillus subtilis (natto) was used to produce poly-gamma-DL-glutamate (γPGA), a polymer of DL-glutamate linked by a γ-peptide bond. In spite of efforts to improve γPGA production by modifying the medium, little attention has been paid to the expression of the γPGA synthetase gene. In this study, we investigated the expression of the γPGA synthetic gene and the γPGA product under various conditions with the LacZ-fusion of the synthetic gene (pgsB-lacZ). The 5′ upstream regulatory region of the pgsB gene was also investigated by constructing deletion mutations of lacZ-fusion. The pgsB-lacZ was clearly expressed in the early stationary phase and was abolished by degU gene disruption. The results showed that pgsB-lacZ expression was repressed in rich media, and that γPGA production was limited by the substrate supply rather than by the amount of synthetase. Adding D-glutamate to the medium reduced γPGA production and synthetic gene expression. The transcription start point was determined by primer extension, and it was found that up to −721 bp (translation start point = +1) of the 5′ untranslated region (UTR) was required for optimal pgsB-lacZ fusion gene expression.