Different patterns of evolution for duplicated DNA repair genes in bacteria of the Xanthomonadales group

Abstract Background DNA repair genes encode proteins that protect organisms against genetic damage generated by environmental agents and by-products of cell metabolism. The importance of these genes in life maintenance is supported by their high conservation, and the presence of duplications of such genes may be easily traced, especially in prokaryotic genomes. Results The genome sequences of two Xanthomonas species were used as the basis for phylogenetic analyses of genes related to DNA repair that were found duplicated. Although 16S rRNA phylogenetic analyses confirm their classification at the basis of the gamma proteobacteria subdivision, differences were found in the origin of the various genes investigated. Except for lexA, detected as a recent duplication, most of the genes in more than one copy are represented by two highly divergent orthologs. Basically, one of such duplications is frequently positioned close to other gamma proteobacteria, but the second is often positioned close to unrelated bacteria. These orthologs may have occurred from old duplication events, followed by extensive gene loss, or were originated from lateral gene transfer (LGT), as is the case of the uvrD homolog. Conclusions Duplications of DNA repair related genes may result in redundancy and also improve the organisms' responses to environmental challenges. Most of such duplications, in Xanthomonas, seem to have arisen from old events and possibly enlarge both functional and evolutionary genome potentiality.

Leptospira interrogans serovar Copenhageni harbors two lexA genes involved in SOS response

Bacteria activate a regulatory network in response to the challenges imposed by DNA damage to genetic material, known as the SOS response. This system is regulated by the RecA recombinase and by the transcriptional repressor lexA. Leptospira interrogans is a pathogen capable of surviving in the environment for weeks, being exposed to a great variety of stress agents and yet retaining its ability to infect the host. This study aims to investigate the behavior of L. interrogans serovar Copenhageni after the stress induced by DNA damage. We show that L. interrogans serovar Copenhageni genome contains two genes encoding putative LexA proteins (lexA1 and lexA2) one of them being potentially acquired by lateral gene transfer. Both genes are induced after DNA damage, but the steady state levels of both LexA proteins drop, probably due to auto-proteolytic activity triggered in this condition. In addition, seven other genes were up-regulated following UV-C irradiation, recA, recN, dinP, and four genes encoding hypothetical proteins. This set of genes is potentially regulated by LexA1, as it showed binding to their promoter regions. All these regions contain degenerated sequences in relation to the previously described SOS box, TTTGN 5CAAA. On the other hand, LexA2 was able to bind to the palindrome TTGTAN 10TACAA, found in its own promoter region, but not in the others. Therefore, the L. interrogans serovar Copenhageni SOS regulon may be even more complex, as a result of LexA1 and LexA2 binding to divergent motifs. New possibilities for DNA damage response in Leptospira are expected, with potential influence in other biological responses such as virulence