Growth of Streptococcus bovis and a Butyrivibrio in batch and continuous culture and the relationship of molar growth yield to intermicrobial competition : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology.

Abstract

Cell growth yield of Streptococcus bovis and Butyrivibrio were determined in batch cultures where growth was separately limited by glucose, CO2 and trypticase. With bovis, glucose limited growth and a Yg of 39.6 g / M in the presence of excess CO2 was determined. S. bovis grew in the absence of CO2 , but the Yg was reduced to 16.5 g / M. In the presence of excess CO2 the Yg determined for Butyrivibrio was 55 g / M. Butyrivibrio was strictly limited by CO2 and the YCO2 was equal to Yg. This led to the suggestion that CO2 metabolism allows the generation of at least two additional ATP when combined with glucose metabolism for both organisms. Monod growth constants were determined for both organisms in continuous culture under glucose limitation. Ks and μmax for S. bovis were 0.429 mM / 1 and 2.47 hr-1 , respectively. For Butyrivibrio, Ks and μmax were 0.332 mM / 1 and 0.704 hr-1 , respectively. The cell growth yields for S. bovis and Butyrivibrio were determined to be 39.6 g / M and 69.1 g / M, respectively. At growth rates less than 0.2 hr-1 colony forming units and total cell counts of S. bovis decreased, but cell yield did not. Colony forming units, total counts and cell growth yield of Butyrivibrio did not decrease at low growth rates. When S. bovis and Butyrivibrio were grown in continuous mixed culture, Butyrivibrio dominated at growth rates below 0.5 hr-1 and growth of S. bovis was strongly depressed. That Butyrivibrio dominated mixed cultures supports the proposition that an organism deriving more ATP per mole of substrate that another will dominate in environments comparable with continuous culture. The roles of maintenance energy, Ks and μmax and cell yield in competition are considered