Analysis of recombination events in DNA mismatch repair genes among Escherichia coli strains belonging to different phylogroups with different mutation frequencies
Abstract number: P629
Objective: The genetic load imposed by the high frequency of mutations might lead to long-term deleterious effects for the mutator population. In this work, we analyze another possibility, "recombinational rescue" rate for wild-type mismatch repair (MMR) genes.
Methods: MMR genes including mutS, mutL, and mutH, as well as those involved in oxidative damage (GO) mutT and mutY, and two housekeeping genes (arcA and fumC) were sequenced in 66 human Escherichia-coli isolates with different mutation frequencies (17 hipo-mutators; 23 normo-mutators; 21 weak-mutators; 5 strong-mutators) and different phylogenetic groups B2 (17), D (16); A (19); and B1 (14). Sixty-nine sequences (including 3 reference sequences) were aligned using ClustalW program, and the best-fit model of nucleotide substitution was selected using jModelTest program. Alignments were analyzed using PhyML, software that estimates maximum likelihood phylogenies. Recombination among aligned sequences was detected using RDPv.3.27 program.
Results: No evidences of recombinational events were found analyzing the housekeeping genes, nor in mutH (MMR) and mutT (GO repair system). Although recombination events were detected in mutY gene (26%) the highest frequency of these events (p < 0.001) was detectable in the MMR genes: mutS (55.07% of sequences analyzed) and mutL (44.93%). Recombination events in mutS gene were higher in weak mutators (71.43%), but interestingly in mutL gene weak mutators showed the lowest rate of recombination (p < 0.05). To avoid phylogenetic noise the sequences with recombination events were eliminated. In this new scenario, D group is still extremely heterogeneous suggesting that new phylogenetic groups must potentially be accepted. Phylogenetic trees of non-recombination events showed higher number of incongruences (when a gene was not clustering with its phylogenetic group) among mutator strains (p < 0.05).
Conclusions: High rates of intragenic recombination occur for the MMR gene mutS, and mutL (high recombination in mutS with low recombination in mutL seems to be a particular feature of weak-mutators). Mutator strains showed significantly higher genetic incongruence. These results suggest that recombinational variation of MMR genes might provide alterations in the mutation frequencies of human E. coli isolates, including "recombinational rescue" of hyper-mutable strains. The classification into four major groups appears to be an oversimplification of a more complex reality.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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