Autoregulation of Lantibiotic Bovicin HJ50 Biosynthesis by the BovK-BovR Two-Component Signal Transduction System in Streptococcus bovis HJ50

Streptococcus bovis HJ50 produces a lacticin 481-like 33-amino-acid-residue lantibiotic, designated bovicin HJ50. bovK-bovR in the bovicin HJ50 biosynthetic gene cluster is predicted to be a two-component signal transduction system involved in sensing signals and regulating gene expression. Disruption of bovK or bovR resulted in the abrogation of bovicin HJ50 production, suggesting both genes play important roles in bovicin HJ50 biosynthesis. Addition of exogenous bovicin HJ50 peptide to cultures of a bovM mutant that lost the capability for bovicin HJ50 production and structural gene bovA transcription in S. bovis HJ50 induced dose-dependent transcription of the bovA gene, demonstrating that bovicin HJ50 production was normally autoregulated. The transcription of bovA was no longer induced by bovicin HJ50 in bovK and bovR disruption mutants, suggesting that BovK-BovR plays an essential role in the signal transduction regulating bovicin HJ50 biosynthesis. A phosphorylation assay indicated that BovK has the ability to autophosphorylate and subsequently transfer the phosphoryl group to the downstream BovR protein to carry on signal transduction. Electromobility shift assays (EMSA) and green fluorescent protein (GFP) reporter gene expression assays showed the specific binding of BovR to the bovA promoter, indicating that BovR regulates bovA expression by direct binding between them. Taken together, bovicin HJ50 biosynthesis is induced by bovicin HJ50 itself and regulated via the two-component signal transduction system BovK-BovR.