Identification and biochemical characterization of membranous short-chain polyglutamate from Bacillus subtilis

It is generally thought that natural strains of Bacillus subtilis produce poly-gamma-glutamate (PGA) as a large exopolymer (over 1,000 kDa) with high water solubility. However, extracellular PGA (ePGA) of B. subtilis is actually diverse in molecular size and configuration. In this study, we identified membranous PGA (mPGA) from both natural and domestic strains of B. subtilis. In contrast to ePGA, mPGA was relatively small and consistently l-glutamate-rich. Genetic analysis revealed that the pgs operon of B. subtilis is responsible for mPGA production as well as ePGA production. Biochemical analyses using the membranous fractions from B. subtilis ssp. chungkookjang indicated that the presence of zinc ions (Zn(2+)) affected both the membrane association of mPGA and in vitro synthesis (elongation) of PGA. Our observations highlighted three important factors that will affect the structural diversity of B. subtilis PGA, namely the occurrence of mPGA, the effects of Zn(2+), and the configuration of glutamate substrate.