Fermentation characteristics of Megasphaera elsdenii J6 derived from pig feces on different lactate isomers

D-Lactate-utilizing bacteria play important roles in maintaining the balance of gut lactate; however, studies on gut D-lactate-utilizing bacteria have been limited. This study aimed to isolate and identify D-lactate-utilizing bacteria from pig gut using the Hungate roll-tube method, and to investigate their metabolic characteristics in vitro. Six different anaerobes were isolated from pig feces, which were identified as related to Bacteroides fragilis, Bacteroides acidifaciens, Veillonella denticariosi, Veillonella caviae, Bacteroides uniformis, and Megasphaera elsdenii based on the 16S rRNA gene sequences. All strains had a significant ability to utilize D-lactate, which was concluded after in vitro fermentation with 25 mmol L−1 D-lactate as the primary carbon source. Of all 6 strains, M. elsdenii J6 showed the highest efficiency of D-lactate utilization and produced a higher ratio of butyrate in total short chain fatty acids (SCFAs). Thus, the in vitro fermentation characteristics of this strain in D-, L-, and DL-lactate mixtures (D-lactate:L-lactate=1:1 or 1:2) were further studied. The results showed that M. elsdenii J6 preferred utilizing D-lactate, and produced more SCFA when using D-lactate as the primary carbon source. The findings suggest that the administration of D-lactate-utilizing bacteria such as M. elsdenii J6 may have a potential advantage in the alleviation of D-lactic acidosis in the animal gut.