Characterization of Bacillus subtilis strains in Thua nao, a traditional fermented soybean food in northern Thailand

Aims: To clarify the diversity of Bacillus subtilis strains in Thua nao that produce high concentrations of products useful in food manufacturing and in health-promoting compounds. Method and Results: Production of amylase, protease, subtilisin NAT (nattokinase), and gamma-polyglutamic acid (PGA) by the Bacillus subtilis strains in Thua nao was measured. Productivity of protease NAT by these strains tended to be higher than by Japanese commercial natto-producing strains. Molecular diversity of isolated strains was analysed via randomly amplified polymorphic DNA-PCR fingerprinting. The strains were divided into 19 types, including a type with the same pattern as a Japanese natto-producing strain. Conclusion: B. subtilis strains that could be a resource for effective production of protease, amylase, subtilisin NAT, or PGA were evident in Thua nao produced in various regions in northern Thailand. Significance and inpact of study: This study clearly demonstrated the value of Thua nao as a potential resource of food-processing enzymes and health-promoting compounds.