ABSTRACT
Spontaneous mutations are important players in evolution. Nevertheless, there is a paucity of information about the mutagenic processes operating in most bacterial species. In this work, we implemented two forward mutational markers for studies in Caulobacter crescentus. We confirmed previous results in which A:T â G:C transitions are the most prevalent type of spontaneous base substitutions in this organism, although there is considerable deviation from this trend in one of the loci analyzed. We also investigated the role of dinB and imuC, encoding error-prone DNA polymerases, in spontaneous mutagenesis in this GC-rich organism. Both dinB and imuC mutant strains show comparable mutation rates to the parental strain. Nevertheless, both strains show differences in the base substitution patterns, and the dinB mutant strain shows a striking reduction in the number of spontaneous -1 deletions and an increase in C:G â T:A transitions in both assays.
ABSTRACT
Mutator strains were identified by screening random Tn5 insertion clones of Caulobacter crescentus. We identified clones with robust increases in mutation rates with Tn5 insertions in the mutY, mutS, mutL and uvrD genes, known to act in mutation-preventing pathways in Escherichia coli. Analysis of mutations in the rpoB gene revealed that in both the parental strain and mismatch repair-deficient mutants, A:TâG:C transitions predominate by a large margin over C:GâT:A. We have also investigated the role of the error-prone polymerase encoded by imuC (dnaE2) in spontaneous mutagenesis, and found that a imuC mutant strain shows mutation rates and sequences comparable to the parental strain. Our study characterizes for the first time mutator strains in a member of the alphaproteobacteria group. In spite of the limitations of using a single marker, possible reasons for the observed mutational bias are discussed in the light of the repertoire of DNA repair genes in this bacterium.
