The mode of action of a group of glycosylated antimicrobial peptides known as glycocins remains to be elucidated. In the current study of one glycocin, sublancin, we identified the phosphoenolpyruvate:sugar phosphotransferase system (PTS) of Bacillus species as a key player in bacterial sensitivity. Sublancin kills several Gram-positive bacteria, such as Bacillus species and Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). Unlike other classes of bacteriocins for which the PTS is involved in their mechanism of action, we show that the addition of PTS-requiring sugars leads to increased resistance rather than increased sensitivity, suggesting that sublancin has a distinct mechanism of action. Collectively, our present mutagenesis and genomic studies demonstrate that the histidine-containing phosphocarrier protein (HPr) and domain A of enzyme II (PtsG) in particular are critical determinants for bacterial sensitivity to sublancin.
Bacteriocins are ribosomally synthesized peptides produced by a wide range of bacterial species. These bacteriocins endow the producing bacteria with a competitive advantage in their respective niche. Many bacteriocins are heavily posttranslationally processed during their biosynthesis, and these modifications are required for activity (1). Nisin is the best-studied bacteriocin and belongs to the lantibiotic family (2). The mode of action of nisin involves binding to lipid II, which prevents further cell wall synthesis, followed by the formation of pores within the membrane. The leakage of essential metabolites from these cells results in death of the bacteria. Targeting of lipid II by bacteriocins is a common mechanism of action (3-5). Other mechanisms include the targeting of phosphotransferase systems (6, 7), acting as Trojan horses (8, 9), parasitizing iron uptake pathways (10) and causing the collapse of membrane potential, together with leakage of ions and/or a decrease in intracellular ATP concentrations (11). There is much interest in bacteriocins for use in the control of bacterial infections and therefore in their mechanisms of action.Sublancin is a bacteriocin produced by the Gram-positive soil bacterium Bacillus subtilis strain 168. It is capable of killing several species of Gram-positive bacteria, such as Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) (12). Sublancin is encoded by the sunA gene on the SP prophage as a prepeptide (13). The genes necessary for the synthesis of sublancin are also included in this region and are expressed from two promoters. The biosynthetic operon is made up of five individual genes, which are responsible for producing active sublancin. The sunT gene is responsible for the export of sublancin and cleavage of its leader sequence. Two thiol-disulfide oxidoreductases, encoded by bdbA (the only gene of the operon that is dispensable for active sublancin production) and bdbB, are responsible for creating the two disulfide bonds of sublancin. These disulfide bonds involve four of the five cysteine re...
