Cloning and Analysis of the l -Lactate Utilization Genes from Streptococcus iniae

Abstract

ABSTRACT The presence of lactate oxidase was examined in eight Streptococcus species and some related species of bacteria. A clone (pGR002) was isolated from a genomic library of Streptococcus iniae generated in Escherichia coli , containing a DNA fragment spanning two genes designated lctO and lctP . We show that these genes are likely to be involved in the l -lactic acid aerobic metabolism of this organism. This DNA fragment has been sequenced and characterized. A comparison of the deduced amino acid sequence of LctP protein demonstrated that the protein had significant homology with the l -lactate permeases of other bacteria. The amino acid sequence of the LctO protein of S. iniae also showed a strong homology to l -lactate oxidase from Aerococcus viridans and some NAD-independent lactate dehydrogenases, all belonging to the family of flavin mononucleotide-dependent α-hydroxyacid-oxidizing enzymes. Biochemical assays of the gene products confirm the identity of the genes from the isolated DNA fragment and reveal a possible role for the lactate oxidase from S. iniae . This lactate oxidase is discussed in relation to the growth of the organism in response to carbon source availability.