Summary auto-generated
This study investigates how class II one-peptide bacteriocins recognize and bind to their targets on bacterial cells. Researchers conducted a phylogenetic analysis of 86 mannose-phosphotransferase system (man-PTS) proteins from diverse bacterial species and found they cluster into three distinct groups. Through experimental testing in a laboratory strain of Lactococcus lactis, they demonstrated that only group I man-PTS proteins function as receptors for class IIa bacteriocins (pediocin-like), while a different group I protein serves as receptor for class IIc bacteriocins. The researchers identified three specific amino acid regions in the IIC and IID protein subunits that distinguish bacteriocin-susceptible from non-susceptible groups. Additionally, they found that among three Lactobacillus sakei strains with identical man-PTS genes, differences in bacteriocin sensitivity correlated with varying expression levels of the man-PTS genes. These findings establish that bacteriocin susceptibility is primarily determined by the specific man-PTS protein structure present on bacterial cells, with gene expression levels playing a secondary but important role.
Key findings
- Only phylogenetic group I man-PTS proteins function as receptors for class IIa bacteriocins, while group I also contains a distinct receptor for class IIc bacteriocins
- Three amino acid sequence regions in man-PTS proteins (two in IIC and one in IID subunits) distinguish bacteriocin-susceptible from non-susceptible bacteria
- Bacteriocin sensitivity can vary among bacterial strains with identical man-PTS genes due to differences in man-PTS gene expression levels
- Man-PTS protein structure is the primary determinant of bacteriocin receptor function, explaining the narrow inhibitory spectra observed for most bacteriocins
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Abstract
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.