Regulation of bacteriocin production by Ruminococcus albus 7

Quorum sensing is a process of bacterial cell-cell communication that uses small molecules to coordinate diverse behaviors in response to population density. The small signal molecules are known as autoinducers, which will cause bacterial response once they reach a threshold level. The efficiency of ruminants to utilize wide variety of feeds is dependent on highly diversified rumen microbial ecosystem. Previous study showed that in vitro cellulose digestion decreased when two major cellulolytic bacteria, Ruminococcus albus and R. flavefaciens were cocultured. R. albus produced bacteriocin to inhibit the growth of R. flavefaciens when they were cocultured. There is not available information about the relationship between quorum sensing and bacteriocin production in R. albus. The purpose of this study is to study the regulation route(s) of bacteriocin production by R. albus.o investigate whether R. albus 7 and R. flavefaciens C94 possess universal LuxS quorum sensing system, we used Vibrio harveyi BB170 bioluminescence assay to test the presence of AI-2 autoinducer. AI-2 reached a maximal activity in late-exponential to early stationary phase of R. albus 7, whereas R. flavefaciens C94 produced less than 1/5 AI-2 activity of R. albus 7 during the same 24 hr incubation period. Furthermore, when R. albus 7 was cocultured with R. flavefaciens C94 or its supernatant, bacteriocin production occurred one hour earlier than R. albus cultured alone. By applying AI-2 obtained from V. harveyi BB152 supernatant, it was found that eight times diluted supernatant stimulated the highest bacteriocin activity and had a similar response pattern as with R. flavefaciens C94 supernatant. Comparing 4, 10, and 24 hr supernatants from R. flavefaciens C94, only the 24 hr supernatant could induce bacteriocin production. But, the AI-2 level was very low in this supernatant compared to the AI-2 level produced by R. albus 7 itself. These results suggested that 24 hr supernatant probably contained certain inducing signal peptide which could stimulate R. albus 7. The proteinaceous material from R. flavefaciens C94 24 hr supernatant was precipitated in sequence with 20, 40, and 60% ammonium sulfate, and purified by size exclusion using FPLC. The result showed that R. flavefaciens C94 had autuinducing peptide with molecular weight between 213 to 5380 Da which could induce bacteriocin production by R. albus 7.n conclusion, bacteriocin production by R. albus 7 could be induced by AI-2 from V. harveyi BB152. In addition, R. albus 7 also can react to the specific autoinducer peptide from R. flavefaciens C94 and produce bacteriocin.