The unusual mode of action of the polyketide glycoside antibiotic cervimycin C

Abstract

Cervimycins A–D are bis-glycosylated polyketide antibiotics produced by <em>Streptomyces tendae</em> HKI 0179 with bactericidal activity against Gram-positive bacteria. In this study, cervimycin C (CmC) treatment caused a spaghetti-like phenotype in <em>Bacillus subtilis</em> 168, with elongated curved cells, which stayed joined after cell division, and exhibited a chromosome segregation defect, resulting in ghost cells without DNA. Electron microscopy of CmC-treated <em>Staphylococcus aureus</em> (3 × MIC) revealed swollen cells, misshapen septa, cell wall thickening, and a rough cell wall surface. Incorporation tests in <em>B. subtilis</em> indicated an effect on DNA biosynthesis at high cervimycin concen trations. Indeed, artificial downregulation of the DNA gyrase subunit B gene (<em>gyrB</em>) increased the activity of cervimycin in agar diffusion tests, and, in high concentrations (starting at 62.5 × MIC), the antibiotic inhibited <em>S. aureus</em> DNA gyrase supercoiling activity <em>in vitro</em>. To obtain a more global view on the mode of action of CmC, transcriptomics and proteomics of cervimycin treated versus untreated <em>S. aureus </em>cells were performed. Interestingly, 3 × MIC of cervimycin did not induce characteristic responses, which would indicate disturbance of the DNA gyrase activity <em>in vivo</em>. Instead, cervimycin induced the expression of the CtsR/HrcA heat shock operon and the expression of autolysins, exhibiting similarity to the ribosome-targeting antibiotic gentamicin. In summary, we identified the DNA gyrase as a target, but at low concentrations, electron microscopy and omics data revealed a more complex mode of action of cervimycin, which comprised induction of the heat shock response, indicating protein stress in the cell.