Effects of a Saccharomyces cerevisiae culture on ruminal bacteria that utilize lactate and digest cellulose.

The objective of this study was to determine the effects of a yeast (Saccharomyces cerevisiae) culture on lactate utilization and cellulose digestion by ruminal bacteria. Growth of Selenomonas ruminantium HD4 in medium that contained 5 g/L of DL-lactate, Trypticase, and yeast extract was stimulated 7 and 15% by 1 and 5% (vol/vol) yeast culture filtrate respectively. The 1 and 5% yeast culture filtrate stimulated growth of Selenomonas ruminantium H18 and Megasphaera elsdenii B159 and T81 on 5 g/L of DL-lactate in medium without Trypticase or yeast extract. Growth of Fibrobacter succinogenes S85 and Ruminococcus albus B199 on 6 g/L of cellobiose was stimulated by the addition of yeast culture filtrate to medium without Trypticase or yeast extract. The yeast culture filtrate increased the concentrations of acetate and total volatile fatty acids that were produced by Sel. ruminantium HD4 and increased the concentrations of propionate and total volatile fatty acids that were produced by Sel. ruminantium H18 but did not alter end-product formation of M. elsdenii or cellulolytic bacteria. Treatment with yeast culture increased the initial rate but not the extent of cellulose digestion by F. succinogenes S85 and Ruminococcus flavefaciens FD1. Collectively, these results suggest that yeast culture provides soluble growth factors (i.e., organic acids, B vitamins, and amino acids) that stimulate growth of ruminal bacteria that utilize lactate and digest cellulose.