Spore-forming Bacillus strains that produce extracellular poly-␥-glutamic acid were screened for their application to natto (fermented soybean food) fermentation. Among the 424 strains, including Bacillus subtilis and B. amyloliquefaciens, which we isolated from rice straw, 59 were capable of fermenting natto. Biotin auxotrophism was tightly linked to natto fermentation. A multilocus nucleotide sequence of six genes (rpoB, purH, gyrA, groEL, polC, and 16S rRNA) was used for phylogenetic analysis, and amplified fragment length polymorphism (AFLP) analysis was also conducted on the natto-fermenting strains. The ability to ferment natto was inferred from the two principal components of the AFLP banding pattern, and natto-fermenting strains formed a tight cluster within the B. subtilis subsp. subtilis group.The Bacillus subtilis species complex is a tight assemblage of related species that includes the laboratory strain B. subtilis subsp. subtilis 168, which has been used as a model organism for 32). B. subtilis subsp. subtilis BEST195, the starter strain used for natto (fermented soybean food) production, is thought to have been isolated about 100 years ago. Since then, it has been distributed to major commercial manufacturers (28). Before the isolation of the starter strain, dried rice straw had been used to initiate natto fermentation; rice straw is the natural habitat of the spore-forming B. subtilis strains that facilitate soybean fermentation. Recently, the entire genome information of the BEST195 strain was published (21). Completion of this project has facilitated the creation of a genomically directed starter cultivation program for natto. Natto starter cultivation targets genes regulating the metabolic pathways of secondary metabolites that affect flavor, sensitivity to bacteriophages, spore formation, and germination.The genome structure of B. subtilis subsp. subtilis BEST195 is very similar to that of the B. subtilis laboratory strain B. subtilis subsp. subtilis 168 (15, 21, 32), but it is not possible to produce natto with the latter (21), apparently due to mutations in the genes degQ and swrA, which regulate poly-␥-glutamic acid (␥PGA) synthesis (27). In contrast, BEST195 actively produces ␥PGA via the pgs operon (1, 2, 4), which provides a sticky texture to natto. However, ␥PGA production alone is not a predictor of the ability to ferment natto, as many ␥PGA-positive strains cannot be used for natto production. These observations have spurred great interest in the genetic basis of natto fermentation ability in Bacillus. Reports on the diversity of natto-fermenting strains are limited to elucidating the genetic background required for natto fermentation. To clarify the taxonomic positions of such strains within the genus Bacillus and to increase genetic sources for cultivating starters, we screened ␥PGA-positive strains from rice straw to determine their abilities to ferment natto.The commercial natto starter strain BEST195 requires biotin for growth. It is sensitive to specific bacteriophages (10, 25)...

We investigated the fate of radioactive cesium ((134)Cs plus (137)Cs) during the production of tofu, natto, and nimame (boiled soybean) from a contaminated Japanese soybean cultivar harvested in FY2011. Tofu, natto, and nimame were made from soybean grains containing radioactive cesium (240 to 340 Bq/kg [dry weight]), and the radioactive cesium in the processed soybean foods and in by-product fractions such as okara, broth, and waste water was measured with a germanium semiconductor detector. The processing factor is the ratio of radioactive cesium concentration of a product before and after processing. For tofu, natto, nimame, and for the by-product okara, processing factors were 0.12, 0.40, 0.20, and 0.18, respectively; this suggested that these three soybean foods and okara, used mainly as an animal feed, can be considered safe for human and animal consumption according to the standard limit for radioactive cesium of soybean grains. Furthermore, the ratio of radioactive cesium concentrations in the cotyledon, hypocotyl, and seed coat portions of the soybean grain was found to be approximately 1:1:0.4.

A new Bacillus subtilis natto-fermenting strain, Miyagi-4100, showing enhanced exoenzyme production and developed from the parental Miyagi-4 strain, was used to prepare natto from hard-hulled black soybeans. In this study, we evaluated the ability of Miyagi-4100 to ferment black soybeans, based on the amount of viscous substances, poly-γ-glutamic acid and levan, as well as the degree of hardness of the fermented black soybean component. Miyagino, a commercial starter strain, and Miyagi-4 were compared to Miyagi-4100. Black soybean natto produced with Miyagi-4100 contained much more levan than that produced with Miyagi-4, and showed a tendency for decreased hardness. Therefore, we conclude that Miyagi-4100 is highly applicable to fermenting black soybeans to natto.

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