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While the detrimental effect of bacteriophages on lactic acid bacterial fermentation is well documented, the importance of Bacillus subtilis phages in soybean-based fermented foods is not. In this study, we show for the first time that 100% of Korean soybean-based fermented foods (Doenjang, Gochujang, and Cheonggukjang) and 70% of raw materials (Meju and rice straw) were contaminated with B. subtilis-infecting phages (as high as 3.7 × 104 PFU g−1). Among 15 isolated B. subtilis-infecting phages, BSP18 was selected for further studies due to its specificity to and relatively broad host infectivity (34%) against B. subtilis. This Myoviridae family phage, BSP18 could infect all of the tested wild-type and commercially-used strains for soybean-based fermented food preparation. Furthermore, artificial contamination of as low as 102 PFU g−1 of BSP18 significantly inhibited B. subtilis growth during Cheonggukjang fermentation. Moreover, phage-treated samples contained considerably more degraded γ-PGA which could negatively affect the functional property of Cheonggukjang. We also present the data, strongly suggesting BSP18-encoded, not bacterial, γ-PGA hydrolase was responsible for γ-PGA degradation. In conclusion, B. subtilis phages are widespread in Korean soybean-based fermented foods and it should be of great concern as phages may hamper the bacterial growth during fermentation and yield poor quality products.

Previous studies on Bacillus subtilis-producing bacteriocins (or bacteriocin-like inhibitory substance, BLIS) against Clostridium perfringens provided with limited information to show their potentials. In this study, B. subtilis BSC35 was newly-isolated and its BLIS-containing cell-free supernatant exhibited a strong antimicrobial activity (maximum 24 mm of lysis zone in standard well diffusion assay) against all the tested C. perfringens strains (22 farm isolates and 2 references). The culture condition was optimized (30 °C, 240 rpm, TSB at pH 7.5) to maximize BLIS BSC35 production and stability of BLIS BSC35 was tested. After zymogram study following partial purification, BLIS BSC35 was measured approximately 4 kDa in size. Finally, when cell-free-supernatant or B. subtilis BSC35 culture was used to control C. perfringens in liquid medium and a food model (Cheonggukjang), as low as 0.1% and 104 CFU/g addition, respectively, was enough to strongly inhibit the growth of C. perfringens with a rapid bactericidal mode of action, implying high anti-C. perfringens potentials and wide range of applicabilities.