Adaptation of Bacillus subtilis MreB Filaments to Osmotic Stress Depends on Influx of Potassium Ions

Abstract

The circumferential motion of MreB filaments plays a key role in cell shape maintenance in many bacteria. It has recently been shown that filament formation of MreB filaments in Bacillus subtilis is influenced by stress conditions. In response to osmotic upshift, MreB molecules were released from filaments, as seen by an increase in freely diffusive molecules, and the peptidoglycan synthesis pattern became less organized, concomitant with slowed-down cell extension. In this study, biotic and abiotic factors were analysed with respect to a possible function in the adaptation of MreB filaments to stress conditions. We show that parallel to MreB, its interactor RodZ becomes more diffusive following osmotic stress, but the remodeling of MreB filaments is not affected by a lack of RodZ. Conversely, mutant strains that prevent efficient potassium influx into cells following osmotic shock show a failure to disassemble MreB filaments, accompanied by less perturbed cell wall extension than is observed in wild type cells. Because potassium ions are known to negatively affect MreB polymerization in vitro, our data indicate that polymer disassembly is directly mediated by the physical consequences of the osmotic stress response. The lack of an early potassium influx response strongly decreases cell survival following stress application, suggesting that the disassembly of MreB filaments may ensure slowed-down cell wall extension to allow for efficient adaptation to new osmotic conditions.