Class II one-peptide bacteriocins target a phylogenetically defined subgroup of mannose phosphotransferase systems on sensitive cells.

Membrane-located proteins (IIC and IID) of the mannose-phosphotransferase system (man-PTS) have previously been shown to serve as target receptors for several bacteriocins. Although many bacteria contain at least one such man-PTS in their genome, most bacteriocins display a narrow inhibitory spectrum, targeting predominantly bacteria closely related to the producers. In the present study we have analysed the receptor spectrum of one-peptide bacteriocins of class II. A phylogenetic analysis of 86 man-PTSs from a wide range of bacterial genera grouped the man-PTSs into three main clusters (groups I-III). Fourteen man-PTSs distributed across the phylogenetic tree were selected for experimental analysis in a heterologous host. Only members of group I could serve as receptors for class IIa bacteriocins, and the receptor efficiencies varied in a pattern directly related to their phylogenetic position. A multiple sequence alignment of IIC and IID proteins revealed three sequence regions (two in IIC and one in IID) that distinguish members of the bacteriocin-susceptible group from those of the other groups, suggesting that these amino acid regions confer the specific bacteriocin receptor function. Moreover, we demonstrated that variation in sensitivity might also exist within the same species due to differential expression levels of the receptor, since three strains of Lactobacillus sakei harbouring identical man-PTSs were shown to display different expression levels of a man-PTS gene that corresponded to the variation in bacteriocin sensitivity. Together, the results of our study show that the level of bacteriocin susceptibility for a bacterial cell is primarily determined by differences in its man-PTS proteins, although the expression levels of the corresponding genes also play an important role.