BACTERIAL COMPETITION BETWEEN A BACTERIOCIN PRODUCING AND A NON-PRODUCING STRAIN OF STREPTOCOCCUS BOVIS IN BATCH AND CONTINUOUS CULTURE

Authors: XAVIER, BRUNO - CORNELL UNIV.; Russell, James

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/2006
Publication Date: 5/1/2006
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 (CD-ROM) Omnipress ISBN 1-55581-389-5. Orlando, FL; May 21-25, 2006 #1054. American Society for Microbiology Annual Meeting.

Interpretive Summary:

Technical Abstract: Cattle are fed antibiotics to alter ruminal fermentation and improve feed utilization, but this non-therapeutic use has been criticized. The European Union will ban antibiotics as growth promotants in 2006, and a similar ban is being debated in the United States. Because bovicin HC5, a bacteriocin from Streptococcus bovis, has the same effect on ruminal fermentation in vitro as the mostly commonly used antibiotic (monensin), it could be an alternative. Experiments were conducted to determine the ability of S. bovis HC5 to compete with S. bovis JB1, a non-bacteriocin producing sensitive strain. We hypothesized that S. bovis HC5 would out-compete S. bovis JB1 but only if cell-free bovicin HC5 had already accumulated. S. bovis HC5 and the control strain, JB1, were co-inoculated into batch and continuous cultures. To assess the out-come of the competition, isolates from the co-cultures were screened for their ability to produce bovicin HC5 and BOX PCR patterns. S. bovis HC5 out-competed JB1 before stationary phase was reached. Even though it grew 10% slower, cell-free bovicin HC5 had not yet accumulated, and the final pH was 6.4. The success of S. bovis HC5 over JB1 was enhanced by the presence of another sensitive bacterium (Clostridium sticklandii SR). When yeast extract and Trypticase were removed, and ammonia was the only nitrogen source, S. bovis JB1 dominated the co-cultures. This latter effect could be explained by the longer lag time (0.5 versus 1.5 h) of 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 S. bovis HC5 once again dominated. Competition in continuous culture was complicated by another avenue of selection (substrate affinity), and batch culture inocula were never able to displace a strain that had already reached steady state even if the inoculum was large. Amplification (PCR) of repetitive DNA sequences (BOX) indicated that S. bovis HC5 was not simply transferring its bacteriocin genes to S. bovis JB1. The bacteriocin, bovicin HC5, gives S. bovis HC5 a growth advantage over a strain that would otherwise be more competitive.