Evolutionary rescue of sphericalmreBdeletion mutants of the rod-shape bacteriumPseudomonas fluorescensSBW25

Abstract

Cell shape is a fundamental property in bacterial kingdom. MreB is a protein 22 that determines rod-like shape, and its deletion is generally lethal. Here, we 23 deleted the mreB homolog from rod-shaped bacterium Pseudomonas fluorescens 24 SBW25 and found that ΔmreB cells are viable, spherical cells with a 20% 25 reduction in competitive fitness and high variability in cell size. We show that 26 cell death, correlated with increased levels of elongation asymmetry between 27 sister cells, accounts for the large fitness reduction. After a thousand generations 28 in rich media, the fitness of evolved ΔmreB lines was restored to ancestral levels 29 and cells regained symmetry and ancestral size, while maintaining spherical 30 shape. Using population sequencing, we identified pbp1A, coding for a protein 31 involved in cell wall synthesis, as the primary target for compensatory mutations 32 of the ΔmreB genotype. Our findings suggest that reducing elongasome 33 associated PBPs aids in the production of symmetric cells when MreB is absent. 34 35

Evolved Biofilm: Review on the Experimental Evolution Studies of Bacillus subtilis Pellicles

“…Discovery of hidden evolutionary pathways in mutant backgrounds goes beyond the biofilms of B. subtilis, and is readily observed in other species, including the parallel evolution of WS morphotypes in Pseudomonas fluorescens when commonly observed adaptation routes are removed [74]. Recently, evolutionary solutions to suboptimal cell shape were studied using a spherical mutant of P. fluorescens, again demonstrating that even seemingly lethal mutations are vincible by compensatory mutations [75].…”

Evolutionary Repair Experiments as a Window to the Molecular Diversity of Life

“…Which Genetic Analyses Were Performed? For most recent evolutionary repair experiments, one of the primary analyses to be performed on evolved clones is wholegenome sequencing [45][46][47]. Comparing ancestral and evolved strains reveals mutations, and two methods identify candidate adaptive mutations: genes that are mutated more often than expected by chance across replicate populations [41], and bulk-segregant analysis [48,49].…”

Polar accumulation of pyoverdin and exit from stationary phase

“…Finally, the rod-cell-shape characteristic of Pseudomonas was considered a possible contributory factor. To test this, pyoverdin accumulation was observed in a spherical Δ mreB mutant [31]. Despite the aberrant cell shape, this mutant displays fluorescence foci of pyoverdin after extended culture (Fig.…”