New crosstalk between probiotics Lactobacillus plantarum and Bacillus subtilis

It was reported that oral administration of Bacillus favored the growth of Lactobacillus in the intestinal tract. Here, this phenomenon was confirmed by co-cultivation of Bacillus subtilis 168 and Lactobacillus plantarum SDMCC050204-pL157 in vitro. To explain the possible molecular mechanisms, B. subtilis 168 cells were incubated in simulated intestinal fluid at 37 °C for 24 h, and up to 90% of cells autolysed in the presence of bile salts. Addition of the autolysate to medium inoculated with Lb. plantarum SDMCC050204 decreased the concentration of H₂O₂ in the culture, alleviated DNA damage and increased the survival of Lb. plantarum, as like the results of exogenous heme addition. These results suggested that the autolysate provided heme, which activated the heme-dependent catalase KatA in Lb. plantarum SDMCC050204. HPLC confirmed the presence of heme in the autolysate. Disruption of the Lb. plantarum SDMCC050204 katA gene abolished the protective effect of the B. subtilis 168 autolysate against H₂O₂ stress. We thus hypothesized that the beneficial effect of Bacillus toward Lactobacillus was established through activation of the heme-dependent catalase and remission of the damage of reactive oxygen species against Lactobacillus. This study raised new crosstalk between the two frequently-used probiotics, highlighting heme-dependent catalase as the key mediator.