EFFECTS OF A STRAIN OF SACCHAROMYCES-CEREVISIAE (LEVUCELL(R) SC1), A MICROBIAL ADDITIVE FOR RUMINANTS, ON LACTATE METABOLISM IN-VITRO

The effect of Levucell(R) SC, a strain of Saccharomyces cerevisiae mar ked as a feed additive for ruminants, was investigated in vitro on lac tate metabolism by the ruminal bacteria Streptococcus bovis and Megasp haera elsdenii. The coculture between 10(7) live cells . mL(-1) of SC and a Streptococcus bovis strain in the presence of glucose reduced la ctate production by the bacterial strain. Live yeast cells were able t o compete with Streptococcus bovis for glucose utilization in strictly anaerobic conditions, so less glucose was available for the bacterium . SC also stimulated L-lactate utilization by a strain of M. elsdenii. The effect depended on the concentration of yeast cells added. Bacter ial growth and fermentation end-product concentrations were also incre ased in the presence of SC. Some amino acids and vitamins, but not dic arboxylic acids, stimulated the bacterial specific activity of L-lacta te uptake. SC was able to provide amino acids to M. elsdenii. In a coc ulture of Streptococcus bovis and M. elsdenii on glucose, the reductio n of lactate concentration was improved by SC, the same trend being ob served when maltose or soluble starch were used as carbon and energy s ource. These results indicate that SC can be a very useful tool to red uce lactate accumulation in vitro during fermentation of soluble sugar s.