Identification and characterization of a Bacillus subtilis strain HB-1 isolated from Yandou, a fermented soybean food in China

Abstract

A Gram-positive Bacillus strain HB-1 was isolated from Yandou, a traditional fermented Chinese soybean product. Comparative 16S rRNA sequence analysis suggested that HB-1 belongs to Bacillus subtilis group without further classification to the individual species. At the same time, Biolog classifying results suggested that HB-1 might be Bacillus licheniformis, one of the eight members in B. subtilis group. In order to determine HB-1 to the species level, the 16S–23S rRNA internal transcribed spacer (ITS) sequences were cloned and analyzed. The analyses indicated that the ITS sequences of HB-1 were 99–100% and 91–92% identical to that of B. subtilis strain 168 and B. licheniformis ATCC 14580, respectively. Thus, the isolated strain HB-1 could be identified as B. subtilis. In addition, neutral protease activity and γ-polyglutamic acid production of strain HB-1 were determined to be 43.4 ± 3.9 U/ml and 9.0 ± 0.6 g/l, respectively. Finally, total viable counts and sensory evaluations were also performed in Yandou prepared in the laboratory by mimicking natural fermentation process. Without inoculation of pure culture, the bacterial number reached a maximum of 8.9 ± 0.7 log 10 CFU/g after 48 h of incubation.