Bacillus subtilis enhances production of Paracin1.7, a bacteriocin produced by Lactobacillus paracasei HD1-7, isolated from Chinese fermented cabbage

Lactobacillus paracasei HD1-7 (CCTCCM 205015), isolated from Chinese sauerkraut fermentation broth, was found to contain the bacteriocin Paracin1.7, which possesses broad-spectrum antibacterial activity. We examined the relationship between bacteriocin production by L. paracasei strain HD1-7 and the cell density of co-cultured bacteria. The cells and supernatants from cultures of different densities of five microbes, four bacteria, and a yeast were co-cultured with L. paracasei HD1-7, and the change in Paracin1.7 levels in the culture broth was measured by the agar-well diffusion method. When the initial cell density of the L. paracasei HD1-7 inoculum was 106 CFU/mL, the strain did not produce bacteriocin, and this was termed the threshold concentration. The five species of microbes tested were grown with added culture supernatant of L. paracasei HD1-7, and the growth of the tested bacteria was inhibited to varying degrees. We found that the supernatants and cells of Bacillus subtilis could induce production of Paracin1.7 in the culture supernatant of L. paracasei HD1-7. Lactobacillus paracasei HD1-7 secretes a bacteriocin called Paracin1.7 into the culture supernatant that inhibits the growth of the four species of bacteria tested, but not Saccharomyces cerevisiae. We found that Bacillus subtilis could increase the concentration of Paracin1.7 in the culture supernatant at a certain threshold cell density. We ultimately showed that this inducer can be purified from the Bacillus subtilis culture supernatant, and that it may be a protein. This study demonstrated that there was a certain ecological relationship between the L. paracasei HD1-7 and other microbes.