Molecular characterization of the possible regulation of multiple bacteriocin production through a three-component regulatory system in Enterococcus faecium NKR-5-3

Enterococcus faecium NKR-5-3 produces multiple-bacteriocins, enterocins NKR-5-3A, B, C, D, and Z (Ent53A, Ent53B, Ent53C, Ent53D, and Ent53Z). However, the biosynthetic mechanisms on how their productions are regulated are yet to be fully understood. In silico analysis revealed putative promoters and terminators in the enterocin NKR-5-3ACDZ gene cluster, and the putative direct repeats (5'-ATTTTAGGATA-3') were conserved upstream of each promoter. Transcriptional analysis by quantitative real-time polymerase chain reaction (PCR) of the biosynthetic genes for the enterocins NKR-5-3 suggested that an inducing peptide (Ent53D) regulates the transcription of the structure genes and corresponding biosynthetic genes of enterocins NKR-5-3, except for Ent53B (a circular bacteriocin), thus consequently regulating their production. Moreover, transcriptional analysis of some knock-out mutants showed that the production of Ent53A, C, D and Z is controlled by a three-component regulatory system (TCS) consisting of Ent53D, EnkR (response regulator), and EnkK (histidine kinase). The production of the circular bacteriocin Ent53B appeared to be independent from this TCS. Nevertheless, disrupting the TCS by deletion of a single component (enkD, enkR and enkK) resulted in a slight increase of enkB transcription and consequently the production of Ent53B, presumably, as an indirect consequence of the increase of available energy to the strain NKR-5-3. Here, we demonstrate the regulatory control of the multiple bacteriocin production of strain NKR-5-3 likely through the TCS consisting of Ent53D, EnkR, and EnkK. The information of the sharing of the regulatory machinery between bacteriocins in strain NKR-5-3 can be useful in its future application such as designing strategies to effectively dispense its multiple bacteriocin arsenal.