A lactate-utilizing bacteria BEY8 was isolated from the pit mud and produced butyrate with lactate. Based on phylogenetic analysis of 16S rRNA gene sequences, strain BEY8 should belong to the genus Clostridium. The most closely related type strain is Clostridium tyrobutyricum DSM 2637, with 99.8％gene similarity. The optimal values of pH for bacterial growth and lactate metabolism were found to be 5.5-6.0. The lag time of bacterial growth and lactate metabolism were observed at pH 4.8 and pH6.5, but finally lactate could be converting to butyrate as main metabolic product. In addition, when the concentration of lactate was more than 156 mM, the lag time of bacterial growth and lactate metabolism were also observed, and the arrearage time increase as increasing lactate concentration, but finally lactate could mainly be convert to butyrate as metabolic product. It was suggested that the isolate has a potential to adapt environment change, and these environmental factors do not affect the change of bacterial metabolic pathway. Furthermore, at pH4.8, the addition of acetate can significantly reduce the lag time of BEY8 growth and improve the metabolic rate of lactate. But acetate could not serve as the sole energy source for bacterial growth, and just as electron acceptor in metabolism of lactate and butyrate production.
