Takanori Kumagai, Yasuyuki Matoba, Masafumi Noda, Masanori Sugiyama, Rumi Miyauchi, Narandalai Danshiitsoodol
We have previously shown that a lactic acid bacterium Lactobacillus (Lb.) brevis 174A isolated from a Citrus iyo fruit produces bacteriocin designated brevicin 174A, which is comprised of two antibacterial polypeptides (designated brevicin 174A-β and 174A-γ). We have also found a gene cluster, composed of eight open reading frames (ORFs), that contains genes for the biosynthesis of brevicin 174A, self-resistance to its own bacteriocin, and two transcriptional regulatory proteins.Some lactic acid bacterial strains have a system to start the production of bacteriocin at an adequate stage of the growth. Generally, the system consists of a membrane-bound histidine protein kinase (HPK) that senses a specific environmental stimulus and a corresponding response regulator (RR) that mediates the cellular response.We have previously shown that although the HPK- and RR-encoding genes are not found on the brevicin 174A biosynthetic gene cluster in the 174A strain, two putative regulatory genes, designated breD and breG, are in the gene cluster.In the present study, we demonstrate that the expression of brevicin 174A production and self-resistance is positively controlled by two transcriptional regulatory proteins, designated BreD and BreG. The BreD is expressed together with BreE as the self-resistance determinant of Lb. brevis 174A. The DNase I footprinting analysis and the promoter assay demonstrate that BreD binds to the breED promoter as a positive autoregulator. The present study also demonstrates that BreG, carrying a transmembrane domain, binds to the common promoter of breB and breC encoding brevicin 174A-β and 174A-γ, respectively, in order to regulate positively.Importance. The problem of appearance of bacteria resistant to practical antibiotics and the increasing demand for safe foods have increased the interest in replacing conventional antibiotics with bacteriocin produced by the lactic acid bacteria. The antibacterial substance can inhibit the growth of pathogenic bacteria without a side-effect to human body. The bacteriocin, which is produced by a Citrus iyo-derived Lactobacillus brevis, inhibits the growth of pathogenic bacteria such as Listeria monocytogenes, Staphylococcus aureus, and Streptococcus mutansIn general, lactic acid bacterial strains have a system to start the production of bacteriocin at an adequate stage of the growth, which is called quorum-sensing system. The system consists of a membrane-bound histidine protein kinase that senses a specific environmental stimulus and a corresponding response regulator that mediates the cellular response. The present study demonstrates that the expression of the bacteriocin biosynthesizing- and self-resistance determinant-encoding genes is positively controlled by two transcriptional regulatory proteins.
