Evolution of Cell Shape in Bacteria

Abstract

In this study, we attempted to understand the evolution of bacterial cell shape, by investigating the function of different proteins involved in cell shape and division in the rod-shaped bacteria Pseudomonas fluorescens, SBW25. This was primarily in the context of the unfit, spherical, asymmetrically dividing ∆mreB mutants of SBW25, that evolved to increase fitness and divide symmetrically after being subjected to a long- term evolution experiment. Firstly, we found that the compensatory point mutation that arose in pbp1A gene in these mutants speculated to cause loss of function was different from the pbp1A deletion mutant in the wildtype background and hence might have an altered function. Secondly, we identified the protein MinC in SBW25, found that it localises to one of the poles of the cell and its inactivation gave rise to cells that had decreased fitness and serious cell division defects dependent on the environment. The study has led to an improvement in bacterial selection techniques, microscopy and bacterial cell morphology quantitation. By providing a better understanding about pbp1A and minC in wildtype cells and improved techniques, the study has opened up the possibility to understand their implications in the fitness and symmetry of division in the evolved and ancestral ∆mreB mutants and has given ∆minC mutant as the next candidate for a long-term evolution experiment.