The Role of SilX in Bacteriocin Production of Streptococcus anginosus

Abstract

Streptococcus anginosus produces the novel antimicrobial peptide Angicin, which inhibits Gram positive microorganisms and is classified as a group IId bacteriocin. Production of Angicin is regulated by the quorum sensing system Sil (Streptococcus invasion locus), which is located adjacent to the bacteriocin gene cluster. Within this genetic region a typical CAAX protease is encoded, which was designated SilX. Nelfinavir, a HIV protease inhibitor, led to a concentration dependent reduction in antimicrobial activity, presumably through the inhibition of SilX. Concentrations exceeding 25 μM Nelfinavir caused a complete abolishment of bacteriocin activity against Listeria monocytogenes. These results are supported by the observation, that a SilX deletion mutant of S. anginosus strain BSU 1211 no longer inhibits the growth of L. monocytogenes. Antimicrobial activity could be restored by addition of synthetically synthesized mature SilCR, implying that SilX may be involved in the export and processing of the signal peptide SilCR. Some CAAX proteases have been reported to provide immunity against bacteriocins. However, in a radial diffusion assay the deletion mutant S. anginosus BSU 1211ΔSilX showed no sensitivity toward Angicin arguing against a role of SilX in the immunity of S. anginosus. The putative processing of the signal peptide SilCR indicates a novel function of the CAAX protease SilX, in the context of S. anginosus bacteriocin production.

Acetate Secretion Induces Bacteriocin Synthesis and Activates the Transcriptional Regulators rgg and rpoD

“…Competition between bacteriocin producers and competitors results in the exclusion of one or the other, depending on their initial ratio, community density and nutrient availability [12]. When the density of the competitor is low, the producer slightly upregulates the production of bacteriocin [28]; when the density of the competitor is much higher than that of the producer, the production of bacteriocin is reduced or the producer cannot become the dominant flora [12]. Therefore, there is positive and negative feedback regulation in the regulation of bacteriocin production by population competition.…”