Abstract
While the harmful effects of lactic acid bacterial bacteriophages in the dairy industry are well-established, the importance of Bacillus subtilis-infecting bacteriophages on soybean fermentation is poorly-studied. In this study, we isolated a B. subtilis-infecting bacteriophage BSP10 from Meju (a brick of dried fermented soybean) and further characterized it. This Myoviridae family bacteriophage exhibited a narrow host range against B. subtilis strains (17/52, 32.7%). The genome of bacteriophage BSP10 is 153,767 bp long with 236 open reading frames and 5 tRNAs. Comparative genomics (using dot plot, progressiveMauve alignment, heat-plot, and BLASTN) and phylogenetic analysis strongly suggest its incorporation as a new species in the Nit1virus genus. Furthermore, bacteriophage BSP10 was efficient in the growth inhibition of B. subtilis ATCC 15245 in liquid culture and in Cheonggukjang (a soybean fermented food) fermentation. Artificial contamination of as low as 102 PFU/g of bacteriophage BSP10 during Cheonggukjang fermentation significantly reduced bacterial numbers by up to 112 fold in comparison to the control (no bacteriophage). Moreover, for the first time, we experimentally proved that B. subtilis-infecting bacteriophage greatly enhanced poly-γ-glutamic acid degradation during soybean fermentation, which is likely to negatively affect the functionalities of Cheonggukjang.
Highlights
Bacillus subtilis is a Gram-positive, endospore-forming bacterium commonly found in soil and the human gut [1]
Bacteriophage BSP10 was isolated from a fermented soybean brick, Meju, by using B. subtilis
Bacteriophage BSP10 was found to be a member of the Myoviridae family with an isometric head (82 ± 8 nm long in diameter; n = 6) and a contractile tail (Figure 1)
Summary
Bacillus subtilis is a Gram-positive, endospore-forming bacterium commonly found in soil and the human gut [1]. It is an industrially important microorganism used for its probiotic activities in humans [2] and for commercial enzyme production [3]. B. subtilis is one of the major fermenting bacteria in soybean-based fermented foods such as Korean Cheonggukjang (a fast-fermented soybean product), Deonjang (fermented soybean paste), Gochujang (hot red pepper paste), and Japanese. Natto [4,5] These types of soybean-based fermented foods are an integral part of the diet of Asian peoples and the market values of these products are increasing day by day [4]. A bacteriophage is a virus that infects host bacteria. The bacteriophage infecting beneficial bacteria are as important as those killing pathogenic bacteria
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