Regulation of polyglutamic acid synthesis by glutamate in Bacillus licheniformis and Bacillus subtilis

Abstract

The synthesis of polyglutamic acid (PGA) was repressed by exogenous glutamate in strains of Bacillus licheniformis but not in strains of Bacillus subtilis, indicating a clear difference in the regulation of synthesis of capsular slime in these two species. Although extracellular gamma-glutamyltranspeptidase (GGT) activity was always present in PGA-producing cultures of B. licheniformis under various growth conditions, there was no correlation between the quantity of PGA and enzyme activity. Moreover, the synthesis of PGA in the absence of detectable GGT activity in B. subtilis S317 indicated that this enzyme was not involved in PGA biosynthesis in this bacterium. Glutamate repression of PGA biosynthesis may offer a simple means of preventing unwanted slime production in industrial fermentations using B. licheniformis.

FIG. 1

Growth of B. licheniformis S173 and PGA biosynthesis in medium containing casein hydrolysate as the nitrogen source. Symbols: □, OD₆₆₀; ◊, PGA accumulation. At the times indicated by the arrows, the cultures were equally divided into two flasks and sodium glutamate was added to 4 g/liter to one of the flasks. Incubation of both flasks continued for 26 h, and the final yield of PGA after incubation in the presence of sodium glutamate is given in milligrams per milliliter above the arrows.

FIG. 2

Molecular size of extracellular PGA from B. licheniformis S 173 as a function of culture age (numbers above lanes represent hours since inoculation). PGA was precipitated from culture supernatant and examined by SDS-PAGE (see text for details).