Direct evidence of recombination in the recA gene of Aeromonas bestiarum

Abstract

tTwo hundred and twenty-one strains representative of all Aeromonas species were characterized usingthe recA gene sequence, assessing its potential as a molecular marker for the genus Aeromonas. The inter-species distance values obtained demonstrated that recA has a high discriminatory power. Phylogeneticanalysis, based on full-length gene nucleotide sequences, revealed a robust topology with clearly sepa-rated clusters for each species. The maximum likelihood tree showed the Aeromonas bestiarum strains ina well-defined cluster, containing a subset of four strains of different geographical origins in a deep inter-nal branch. Data analysis provided strong evidence of recombination at the end of the recA sequences inthese four strains. Intergenomic recombination corresponding to partial regions of the two adjacent genesrecA and recX (248 bp) was identified between A. bestiarum (major parent) and Aeromonas eucrenophila(minor parent). The low number of recombinant strains detected (1.8%) suggests that horizontal flowbetween recA sequences is relatively uncommon in this genus. Moreover, only a few nucleotide differ-ences were detected among these fragments, indicating that recombination has occurred recently. Finally,we also determined if the recombinant fragment could have influenced the structure and basic functionsof the RecA protein, comparing models reconstructed from the translated amino acid sequences of ourA. bestiarum strains with known Escherichia coli RecA structures.