Stabilization of γ-PGA Production by a recA Mutant in Bacillus subtilis

Abstract

Natto is a traditional Japanese food with a unique viscous property. The viscous property mainly derives from the poly-γ-glutamate (γ-PGA) produced by Bacillus subtilis, the so-called natto bacterium, during the fermentation of steamed soybeans. However, the γ-PGA-producing ability of B. subtilis is easily lost by insertion sequence (IS) transposition to the comP locus. We isolated a recA-deficient mutant, and evaluated the γ-PGA production and IS transposition in B. subtilis. After repeated passages, the parent strain lost the γ-PGA-producing ability whereas the recA-deficient strain retained it; IS transposition to the comP locus was observed in the parent strain, but not in the recA mutant. Furthermore, the amount of γ-PGA produced by the parent strain in natto was reduced to less than 1/10 that of the recA mutant. These findings suggest that the recA mutant may stabilize the viscous property of natto fermented food.