Bacterial competition between a bacteriocin-producing and a bacteriocin-negative strain of Streptococcus bovis in batch and continuous culture

Abstract

A bacteriocin-producing Streptococcus bovis strain (HC5) outcompeted 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 coinoculated into minimal medium, bacteriocin-negative isolates predominated, and this effect could be explained by the longer lag time (0.5 vs. 1.5 h) of S. bovis HC5. If the glucose concentration of the minimal medium was increased from 2 to 7 mg mL(-1), the effect of lag time was diminished and bacteriocin-producing isolates once again dominated the coculture. 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.

The activity and stability of cell-associated activity of bovicin HC5, a bacteriocin from Streptococcus bovis HC5

“…Clostridium sticklandii SR is more sensitive to bovicin HC5 than S. bovis JB1 (Mantovani & Russell, 2003), but coculture experiments indicated that S. bovis JB1 was inhibited by S. bovis HC5 if the pH was 6.7 (Xavier & Russell, 2006), a pH where little potassium efflux is seen. Breukink and his colleagues (Breukink et al , 2003; Martin & Breukink, 2007) indicated that that nisin had two different activities, pore formation and a direct inhibition of peptidoglycan formation via its interaction with lipid II.…”