Subtilisin NAT, a subtilisin-like serine protease present in fermented soybean “natto” extract, inhibits Streptococcus mutans biofilm formation

Abstract

Our previous study indicated that the water-soluble extract obtained from commercially available natto products inhibited the sucrose-dependent cariogenic biofilm formation of Streptococcus mutans. This inhibitory effect correlated with the protease activity levels of the extract. Subtilisin NAT (nattokinase), a subtilisin-like serine protease, is a dominant protease found in natto products. In this study, we investigated the effect of natto products produced by a subtilisin NAT-deficient mutant (aprN⁻) of the Bacillus subtilis strain NBRC16449 on S. mutans biofilm formation. The mutation decreased the γ-poly glutamic acid (γ-PGA) levels and reduced protease activity in natto products. A significant reduction of the inhibitory effect was observed in the extract from natto products prepared with the aprN⁻ strain. The γ-PGA obtained from the natto products did not affect biofilm formation. We propose that subtilisin NAT plays a major role in biofilm inhibition induced by natto extract.