THE ERROR-PRONE DNA POLYMERASES ImuB AND DnaE2 CONTRIBUTE TO STRESS-INDUCED MUTAGENESIS IN Pseudomonas aeruginosa

Córdoba

Congreso; XI CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2015

DNA damage-induced mutagenesis is, in a major extent, an active process that requires specialized DNA polymerases able to perform translesion synthesis. The expression of these specialized polymerases is usually governed by the SOS system, a stress-inducible response that is activated when cells need to be rescued from severe DNA damage. These DNA polymerases, which belong to the Y family of DNA polymerases, diverge from the typical replicative DNA Pols I and III in their low fidelity and processivity, and the lack of 3?→5? proof-reading exonuclease activity. Thus, induction of the Y-family of DNA polymerases serves to increase the probability of survival under stressful conditions in exchange for an error-prone DNA synthesis, which bestowed them the name of ?mutagenic polymerases?. Pseudomonas aeruginosa is an opportunistic pathogen and the main cause of morbidity and mortality in patients with cystic fibrosis (CF) due to chronic airways infections. It has been established that in order to persist, P. aeruginosa undergoes a mutation-based adaptive process. This process may therefore, be influenced by factors which are able to alter the mutation rate such as the activity of mutagenic polymerases. Inspection of P. aeruginosa genome reveals the presence of a dinB-enconded Pol IV and also of a three-gene cassette imuA-imuB-dnaE2. In this sense, it has been shown that Pol IV constitutes a SOS-dependent error-prone DNA polymerase of P. aeruginosa, being involved in the acquisition of prototypic CF adaptive phenotypes such as mucoidy and antibiotic resistance. However, little is known about other putative error-prone DNA polymerases such as imuB and dnaE2. Here we have investigated the role of these two putative DNA polymerases in P. aeruginosa DNA-damage induced mutagenesis. The results obtained show that both genes contribute to UV-induced mutagenesis in this bacterium. DNA sequencing of the rpoB gene in rifampicin-resistant mutants suggests that ImuB and DnaE2 participate in the generation of A:T-T:A transversion mutations. Furthermore, UV treatment significantly increased the expression levels of imuB and dnaE2 transcripts. Interestingly, expression of imuB and dnaE2 was abolished in a lexA-deficient strain suggesting that both genes are controlled by the SOS regulon in P. aeruginosa. We subsequently analyzed the transcriptional organization of imuB and dnaE2 and observed that these genes behaved as a single transcriptional unit, thereby constituting an operon. On the whole, these results contribute to shed light on the wide repertory of adaptive responses of P. aeruginosa to thrive in hostile environments such as the airways of CF patients.