Efficient production of poly(γ-glutamic acid) by newly isolated Bacillus subtilis NX-2

A bacterium with high poly(gamma-glutamic acid) ( gamma-PGA) productivity was isolated from soil. The bacterial strain NX-2 was identified taxonomically as Bacillus subtilis with the exception that it could not assimilate citric acid. The production of gamma-PGA was investigated. Exogenous glutamic acid and additional carbon source was necessary for the production of y-PGA. The suitable carbon sources were glucose, sucrose, maltose, starch and glycerol. However, gamma-PGA could not be produced when citric acid was used as carbon sources, which is different from the other bacteria reported before. The amount of gamma-PGA increased upon addition of glutamic acid to the medium. When 70 g/l of L-glutamic acid was added to the medium, the highest y-PGA concentration of 41 g/l was obtained. But the apparent conversion rate to L-glutamic acid substrate was relatively low, only 58% in this case. The amount of -y-PGA reached 30.2 g/l in the presence of 30 g/l L-glutamic acid after the short incubation time of 24 h, resulting in the high apparent conversion rate of 101% and high productivity of 1.26 g/l/h. The total amount of glutamic acid including that accumulated in gamma-PGA and residual glutamic acid in broth was much more than the glutamic acid supplied to the medium. The yield of -y-PGA also exceeded the amount of glutamic acid came from glucose conversion. This showed that the glutamic acid units in gamma-PGA not only came from the glutamic acid added to the medium but also from glucose through the de novo pathway of glutamic acid synthesis. (C) 2003 Elsevier Ltd. All rights reserved.