Vibrio cholerae shows differential behavior along a Long Term Evolution Experiment (LTEE) according to the positioning of ribosomal protein genes.

ALFONSO SOLER BISTUE; PIERRE FAURE; JULIE LAMBERT; VARUN KHANA

Roskoff

Congreso; The Vibrio Meeting 2016; 2016

It is unclear how gene order within the chromosome influences bacterial evolution. Bioinformatic studies have shown that translation genes, in particular ribosomal protein genes (RP), are located near the replication origin (oriC) in fast-growing bacteria. We recently relocated half of RP to different genomic loci in Vibriocholerae, revealing important differences in growth rate (GR) and  infectivity within this isogenic strain set. Competition experiments showed that the relocation of RP far-away from oriC impairs fitness of such strains. These evidences indicate that RP location may influence genome evolution. To further understand this issue, we evolved 3 populations of either the wild type (wt) or the most affected strains, where RP genes were located far from oriC (movants), for 1000 generations in fast-growing conditions. Along the LTEE, all populations showed an increment in GR. WT populations showed a sudden increment at 250 generations while movants showed smaller improvement at later stages. Competition experiments done in rich medium revealed a modest fitness improvement in the populations. In minimal media, we noticed an unexpected big fitness increase at 250 generations followed by continuous reduction along LTEE. In both conditions, fitness differences between wt and the movant populations persisted. After 350generations, all populations developed rugose phenotype clones associated to aggregates and biofilms. NGS was performed on one wt and one movant population to determine mutations associated to the phenotypic changes. After250 generations 1 mutation was fixed per population. After 1000 generations,the wt population fixed 26 mutations while we found only 3 mutations in the movant population suggesting a slow evolution rate of the latter.Interestingly, mutations occurred on genes linked to LPS synthesis, flagellum,QS and translation. In sum, biofilm was a common adaptation to in vitro culture. RP location conditioned the evolution of GR, fitness and, possibly,the mutation rate.