Production of Ruminococcus flavefaciens growth inhibitor(s) by Ruminococcus albus

While trying to develop a most probable number (MPN) selective medium for the enumeration of Ruminococcus albus 7 and Ruminococcus flavefaciens B1a in coculture, it was observed that when cultures of the two organisms were mixed for testing the media, growth of R. flavefaciens B1a was inhibited. Subsequent studies indicated that R. albus 7 produced an inhibitory substance that was present in cell-free culture filtrates and the extent of inhibition increased with the quantity of R. albus filtrate. R. albus, MO2a and MO3g were also tested for inhibitory activity against R. flavefaciens B1a, B34b, R13e2 and C1a, Fibrobacter succinogenes S85 and Butyrivibrio fibrisolvens H17c. R. flavefaciens B1a and C1a were found to be inhibited by all strains of R. albus and strain B34b was inhibited by R. albus MO2a and MO3g. The inhibitory substance(s) was heat-labile and destroyed by protease. When R. albus strains were cocultured with a proteolytic organism isolated from the rumen, B. fibrisolvens H17c, inhibitory activity was decreased or completely destroyed. These results suggest that the inhibitory material is proteinaceous and may be a bacteriocin-like compound.