Membrane-targeting antimicrobials trigger lysis in Bacillus subtilis by disturbing the MreB-dependent regulation of peptidoglycan hydrolases

Abstract

Membrane-targeting antimicrobials are generally assumed to kill bacteria through bacteriolysis induced by the permeabilisation of the cytoplasmic membrane. This model relies on the notion that bacteriolysis is the direct cellular manifestation of the membrane-disruptive (membranolytic) activity of an antibacterial compound. However, it underappreciates the key role of peptidoglycan hydrolases in bacteriolysis. Using the Gram-positive model organism Bacillus subtilis, we demonstrate that the bacteriolytic activity of membrane-targeting antimicrobials arises from the misregulation of peptidoglycan hydrolases, regardless of whether they induce large membrane pores or trigger more subtle membrane disturbances such as depolarisation. Contrary to previous models, the autolysis of B. subtilis induced by membrane depolarising compounds does not depend on pH changes associated with the cell surface. Instead, the autolytic process is triggered by membrane depolarisation-dependent dissociation of the bacterial actin homolog MreB, a key spatial coordinator of cell wall synthesis in rod-shaped bacteria, from the cytoplasmic membrane. These findings provide valuable insights into the cellular pathways involved in autolysis, highlight the challenges in distinguishing between direct and indirect cellular effects of membrane-targeting antibiotics, and improve our understanding of antibiotic-induced bacteriolysis.