Bacillus subtilis with a 1% population enhances the activity of Enterococcus faecalis with a 99% population

Abstract

Microbes are present as communities in the environment. However, the importance of minor populations has not been well studied experimentally. In this study, we evaluated the role of Bacillus subtilis with a 1% population and its effect on co-incubated Enterococcus faecalis with a 99% population. Here we used an azo dye-decolorizing Enterococcus faecalis strain T6a1 and non-dye-decolorizing Bacillus subtilis strain S4ga. The dye decolorization assay enabled the investigation of the effects of Bacillus subtilis S4ga on the activity of Enterococcus faecalis T6a1, even when Bacillus subtilis S4ga was present at only 1% relative abundance or lower. We found that non-decolorizing Bacillus subtilis S4ga enhanced the dye decolorization activity of Enterococcus faecalis T6a1, shortened the lag time of Enterococcus faecalis T6a1 to start decreasing the dye concentration, and increased the time for Enterococcus faecalis T6a1 to continue dye decolorization. These effects were correlated with redox potential values. We compared the extracellular amino acids between each incubation culture of Enterococcus faecalis T6a1 and Bacillus subtilis S4ga, which revealed their mutual relationship by cross-feeding of specific amino acids. We also compared the intracellular primary metabolites between co-incubation and sole incubation of E. faecalis T6a1. The arginine deiminase (ADI) pathway in the co-incubated E. faecalis T6a1 was activated compared to that of E. faecalis T6a1 incubated solely. These findings explained that co-incubation with Bacillus subtilis S4ga promoted ATP production in Enterococcus faecalis T6a1 cells to a greater extent and enhanced dye-decolorization activity.