Submitted to: Federation of European Microbiological Societies Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2006
Publication Date: 12/15/2006
Citation: Xavier, B.M., Russell, J.B. 2006. Bacterial competition between a bacteriocin producing and a non-producing strain of streptococcus bovis in batch and continuous culture. Federation of European Microbiological Societies Microbiology Ecology. 58:317-322.
Interpretive Summary: Cattle in the U.S. are often fed antibiotics, but the widespread use of antibiotics in animal feed has been criticized. Antibiotics are primarily targeted against gram-positive gut bacteria. Gram-positive ruminal bacteria produce large amounts of hydrogen a precursor of methane, ammonia, a wasteful end-product of amino acid degradation, and lactic acid, an acid that causes ruminal acidosis, ruminal ulcers, founder and even death of the animal. Some bacteria produce peptides (bacteriocins) that can inhibit gram-positive bacteria, and bacteriocins have been proposed as an alternative to antibiotics. In this paper, we describe the ability of a bacteriocin producing strain of Streptococcus bovis to compete with one that does not produce bacteriocin. Results indicated that bacteriocin producer was, in most cases, able to out-compete the other. Research on bacteriocins has the potential to decrease the need for antibiotic in animal feed.
Technical Abstract: A bacteriocin-producing Streptococcus bovis strain (HC5) out-competed a sensitive strain (JB1) before it reached stationary phase (pH 6.4) even though it grew 10% slower and cell-free bovicin HC5 could not yet be detected. The success of bacteriocin-negative S. bovis isolates was enhanced by the presence of another sensitive bacterium (Clostridium sticklandii SR). PCR based on repetitive DNA sequences indicated that S. bovis HC5 was not simply transferring bacteriocin genes to S. bovis JB1. When the two S. bovis strains were co-inoculated into minimal medium, bacteriocin-negative producing isolates predominated, and this effect could be explained by the longer lag time (0.5 versus 1.5 h) of S. bovis HC5. If the glucose concentration of the minimal medium was increased from 2 to 7 mg per ml, the effect of lag time was diminished and bacteriocin-producing isolates once again dominated the co-culture. When the competition was examined in continuous culture, it became apparent that batch culture inocula were never able to displace a strain that had already reached steady state, even if the inoculum was large. This result indicated that bacterial selection for substrate affinity was even more important than bacteriocin production.