Antimicrobial peptide sublancin - mechanism of its function and resistance

Sublancin is a highly stable 37 amino-acid antimicrobial peptide synthesised by the Gram- positive soil bacterium Bacillus subtilis. Sublancin is bactericidal against many Gram-positive bacteria, including clinically significant pathogens of the Streptococcus and Staphylococcus genera. This makes sublancin a potential candidate for clinical applications. However, despite decades of research, the mechanism of action of this antimicrobial peptide has not yet been elucidated. Previous results from whole-genome sequencing of sublancin-resistant B. subtilis mutants obtained in our laboratory revealed two genes - glcR and ptsG - as key determinants of sublancin sensitivity. GlcR is a poorly characterised transcription factor acting as a negative regulator of its own operon. PtsG is a membrane permease of the phosphotransferase system (PTS) composed of three domains (IIB, IIA, IIC), which are responsible for transporting glucose into the cell. In this Thesis, sublancin was purified from the B. subtilis culture supernatant and its activity was tested against B. subtilis deletion mutants lacking glcR and ptsG. Results of these experiments revealed that the loss of glcR and ptsG in a sublancin-sensitive strain results in full resistance to sublancin. Subsequent in vitro transcription assays with purified...