Characteristics of the bovicin HJ50 gene cluster in Streptococcus bovis HJ50

1 State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China 2 Graduate University of Chinese Academy of Sciences, Beijing 100039, PR China 3 Center for Metabolic Engineering of Microorganisms, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China Correspondence Jin Zhong zhongj{at}sun.im.ac.cn Bovicin HJ50 is a new lantibiotic containing a disulfide bridge produced by Streptococcus bovis HJ50; its encoding gene bovA was reported in our previous publication. To identify other genes involved in bovicin HJ50 production, DNA fragments flanking bovA were cloned and sequenced. The bovicin HJ50 biosynthesis gene locus was encoded by a 9.9 kb region of chromosomal DNA and consisted of at least nine genes in the following order: bovA , - M , - T , - E , - F, ORF1, ORF2, bovK and bovR . A thiol–disulfide oxidoreductase gene named sdb1 was located downstream of bovR . A knockout mutant of this gene retained antimicrobial activity and the molecular mass of bovicin HJ50 in the mutant was the same as that of bovicin HJ50 in S. bovis HJ50, implying that sdb1 is not involved in bovicin HJ50 production. Transcriptional analyses showed that bovA, bovM and bovT constituted an operon, and the transcription start site of the bovA promoter was located at a G residue 45 bp upstream of the translation start codon for bovA , while bovE through bovR were transcribed together and the transcription start site of the bovE promoter was located at a C residue 35 bp upstream of bovE . We also demonstrated successful heterologous expression of bovicin HJ50 in Lactococcus lactis MG1363, which lacks thiol–disulfide oxidoreductase genes; this showed that thiol–disulfide oxidoreductase genes other than sdb1 are not essential for bovicin HJ50 biosynthesis. Present address: Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. The GenBank/EMBL/DDBJ accession number for the bovicin HJ50 biosynthesis gene cluster is EU497962.