Ruminococcin C, a new anti-Clostridium perfringens bacteriocin produced in the gut by the commensal bacterium Ruminococcus gnavus E1.

When colonizing the digestive tract of mono-associated rats, Ruminococcus gnavus E1 - a bacterium isolated from human faeces - produced a trypsin-dependent anti-Clostridium perfringens substance collectively named Ruminococcin C (RumC). RumC was isolated from the caecal contents of E1-monocontaminated rats and found to consist of two antimicrobial fractions: a single peptide (RumCsp) of 4235 Da, and a mixture of two other peptides (RumCdp) with distinct molecular masses of 4324 Da and 4456 Da. Both RumCsp and RumCdp were as effective as metronidazole in combating C. perfringens and their activity spectra against different pathogens were established. Even if devoid of synergistic activity, the combination of RumCsp and RumCdp was observed to be much more resistant to acidic pH and high temperature than each fraction tested individually. N-terminal sequence analysis showed that the primary structures of these three peptides shared a high degree of homology, but were clearly distinct from previously reported amino acid sequences. Amino acid composition of the three RumC peptides did not highlight the presence of any Lanthionine residue. However, Edman degradation could not run beyond the 11th amino acid residue. Five genes encoding putative pre-RumC-like peptides were identified in the genome of strain E1, confirming that RumC was a bacteriocin. This is the first time that a bacteriocin produced in vivo by a human commensal bacterium was purified and characterized.

Production of an antibacterial substance in the digestive tract involved in colonization-resistance against Clostridium perfringens.

Ruminococcus gnavus E1, Bacteroides thetaiotaomicron LEMF4, Clostridium hathewayi LEMC7, and Clostridium orbiscindens LEMH9 were isolated from ex germ-free mice inoculated with a human faecal microbiota. When initially germ-free mice who were previously inoculated with the strain E1 alone, or a four-strain consortium [E1, LEMF4, LEMC7, and LEMH9], were then challenged with 108 counts of Clostridium perfringens; the target strain was rapidly eliminated from the digestive tract of the animals (<10² cfu g⁻¹ of faeces). R. gnavus E1 was able to produce a diffusible anti-C. perfringens substance that accumulated in the faeces of monoassociated animals, but failed to be detected in the faeces of mice associated with the four-strain consortium. The capability to produce the antibacterial substance was transferred in the digestive tract of gnotobiotic mice to a Dorea longicatena strain. Further experiments realized with the D. longicatena wild type strain and the transconjugant support the assumption that the diffusible antibacterial substance was necessary for obtaining the antagonistic effect against C. perfringens, but that it acted as a precursor in the mechanism of interaction of the four-strain consortia.