FACTORS AFFECTING LACTATE AND MALATE UTILIZATION BY SELENOMONAS-RUMINANTIUM

Lactate utilization by Selenomonas ruminantium is stimulated in the pr esence of malate. Because little information is available describing l actate-plus-malate utilization by this organism, the objective of this study was to evaluate factors affecting utilization of these two orga nic acids by two strains of S. ruminantium. When S. ruminantium HD4 an d H18 were grown in batch culture on DL-lactate and DL-malate, both st rains coutilized both organic acids felt the initial 20 to 24 h of inc ubation and acetate, propionate, and succinate accumulated. However, w hen malate and succinate concentrations reached 7 mM, malate utilizati on ceased, and with strain H18, there was a complete cessation of DL-l actate utilization. Malate utilization by both strains was also inhibi ted in the presence of glucose. S. ruminantium HD4 was unable to grow on 6 mM DL-lactate at extracellular pH 5.5 in continuous culture (dilu tion rate, 0.05 h(-1)) and washed out of the culture vessel. Addition of 8 mM DL-malate to the medium prevented washout on 6 mM DL-lactate a t pH 5.5 and resulted in succinate accumulation. Addition of malate al so increased bacterial protein, acetate, and propionate concentrations in continuous culture. These results suggest that 8 mM DL-malate enha nces the ability of strain HD4 to grow on 6 mM DL-lactate at extracell ular pH 5.5.