SERINE UTILIZATION AS A POTENTIAL COMPETITION MECHANISM BETWEEN SALMONELLA AND A CHICKEN CECAL BACTERIUM

Our objective in this study was to use batch culture to estimate growth kinetic parameters for a growth-limiting amino acid, serine, in Salmonella typhimurium and a in chicken cecal bacterium, Escherichia fergusonii, and to test these predictions for competitiveness in a mixed culture of the two organisms. Under anaerobic growth conditions, the two bacteria grew only when serine was provided as the nitrogen source. When serine was used as a carbon source in aerobic media, the maximum growth rates of the two organisms were considerably lower and the affinity constants were higher than when serine was used as a nitrogen source. The maximum growth rates of the two organisms were lower in anaerobic media than in aerobic media, but serine anaerobic affinity constants were lower than those from aerobic media. In aerobic mixed culture, S. typhimurium outgrew E. fergusonii in N-limited minimal media containing 0.1 mM serine but in N-nonlimited minimal media containing 10 mM serine, E. fergusonii outgrew S. typhimurium. In anaerobic mixed culture, E. fergusonii outgrew S. typhimurium in media containing both 0.1 mM and 10 mM serine concentrations. It appears that the cause of inhibition of Salmonella with serine as the variable nutrient differs depending on the oxidation-reduction status.