Kavli Affiliate: Michael Miller
| Authors: Paul Richard Yulo, Nicolas Desprat, Monica L. Gerth, Barbara Ritzl-Rinkenberger, Andrew D Farr, Yunhao Liu, Xue-Xian Zhang, Michael Miller, Felipe Cava, Paul B. Rainey and Heather L Hendrickson
| Summary:
Maintenance of rod-shape in bacterial cells depends on the actin-like protein MreB. Deletion of mreB from Pseudomonas fluorescens SBW25 results in spherical cells of variable volume and reduced fitness. Using a combination of time-resolved microscopy and biochemical assay of peptidoglycan synthesis we show that reduced fitness is a consequence of the production of non-viable cells that arise from unequal septation, but primarily from differential growth (elongation) of daughter cells due to heterogeneity in cell wall synthesis. A 1,000-generation selection experiment resulted in rapid restoration of fitness with derived cells retaining spherical shape, but having reduced cell volume. Mutations in the peptidoglycan synthesis protein Pbp1A were identified in four replicate lineages with genetic reconstructions demonstrating causal connections to fitness compensation. The pbp1A mutations targeting transpeptidase activity reduced variation in elongation rate among daughter cells by restoring homogeneity of cell wall synthesis on lateral surfaces. Together our experimental approach emphasizes the value of strategies that exploit the power of natural selection to rescue fitness-compromised mutants.