Effects of an Aspergillus oryzae fermentation extract and other factors on lactate utilization by the ruminal bacterium Megasphaera elsdenii.
The objective of this study was to determine the effects of an Aspergillus oryzae fermentation extract (Amaferm) as well as other factors on lactate utilization by the ruminal bacterium Megasphaera elsdenii B159. Addition of Amaferm or a filter-sterilized Amaferm filtrate stimulated L-lactate uptake by both M. elsdenii and the ruminal selenomonad strain H18. Growth of M. elsdenii in medium that contained DL-lactate (2 g/L), Trypticase, and yeast extract was only slightly stimulated by the addition of 5% (vol/vol) Amaferm filtrate after 24 h. However, growth of M. elsdenii in a similar medium lacking Trypticase and yeast extract was increased over twofold by the addition of either 2 or 5% (vol/vol) Amaferm filtrate. These results suggest that Amaferm provides growth factors (i.e., amino acids, B vitamins) to support growth of M. elsdenii on lactate. There was no inhibition of L-lactate uptake when lactate-grown cells of M. elsdenii were incubated with excess (10 mM) glucose, sucrose, or maltose. In addition, when cells were grown on glucose, sucrose, or maltose rather than lactate there was little difference in L-lactate uptake, suggesting that L-lactate transport in M. elsdenii is not subject to catabolite repression by these soluble sugars. Both K+ and Na+ had little effect on L-lactate uptake. Uptake was unaffected at extracellular pH values between 6.0 and 8.0, whereas pH values of 5.0 and 4.0 increased uptake. In addition, L-lactate uptake was inhibited between 34 and 61% by protonophores. These results suggest that protons may be involved in the uptake of L-lactate by M. elsdenii B159.