Isolation and characterization of Escherichia coli mutant strains sensitive to 2-aminopurine

MARTINA, M. A.; NAVARRO, A.; BARRA, J. L.

San Luis

Congreso; XLVII Reunión anual SAIB; 2011

SAIB

Escherichia coli strains deficient in DNA adenine methyltransferase (Dam) are soft mutators but their mutation rate rapidly increase in the presence of mutator agents like the base analogue 2-aminopurine (2AP). Although this increment in mutation rate could represent and adaptive advantage under stress conditions, as Dam methylation is important for expression of a number of virulence factors, dam cells of several bacteria strains are attenuated.

Therefore, we screened an E. coli library searching for strains sensitive to 2AP but that retain their DNA methylation capacity. We found two strains with these characteristics.

Complementation assays showed that overexpression of the wild type dam gene reverts the sensitivity to 2AP of one of these strains. DNA sequencing of the endogenous dam gene let us identify a mutation in the coding sequence of the gene as well as others in the 5´ region that could be affecting the promoter regulation. This suggested that a mutant, but still functional, Dam protein or an altered expression of this protein could be responsible for the phenotype of these strains. We are currently analyzing the molecular mechanism responsible for this phenotype and the putative adaptive advantage of these strains.