tailieunhanh - Báo cáo y học: "Small variable segments constitute a major type of diversity of bacterial genomes at the species level"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Small variable segments constitute a major type of diversity of bacterial genomes at the species level. | Touzain et al. Genome Biology 2010 11 R45 http 2010 11 4 R45 w Genome Biology RESEARCH Open Access Small variable segments constitute a major type of diversity of bacterial genomes at the species level 12 3 4 1 1 Fabrice Touzain Erick Denamur Claudine Médigue Valérie Barbe Meriem El Karoui Marie-Agnès Petit Abstract Background Analysis of large scale diversity in bacterial genomes has mainly focused on elements such as pathogenicity islands or more generally genomic islands. These comprise numerous genes and confer important phenotypes which are present or absent depending on strains. We report that despite this widely accepted notion most diversity at the species level is composed of much smaller DNA segments 20 to 500 bp in size which we call microdiversity. Results We performed a systematic analysis of the variable segments detected by multiple whole genome alignments at the DNA level on three species for which the greatest number of genomes have been sequenced Escherichia coli Staphylococcus aureus and Streptococcus pyogenes. Among the numerous sites of variability 62 to 73 were loci of microdiversity many of which were located within genes. They contribute to phenotypic variations as 3 to 6 of all genes harbor microdiversity and 1 to 9 of total genes are located downstream from a microdiversity locus. Microdiversity loci are particularly abundant in genes encoding membrane proteins. In-depth analysis of the E. coli alignments shows that most of the diversity does not correspond to known mobile or repeated elements and it is likely that they were generated by illegitimate recombination. An intriguing class of microdiversity includes small blocks of highly diverged sequences whose origin is discussed. Conclusions This analysis uncovers the importance of this small-sized genome diversity which we expect to be present in a wide range of bacteria and possibly also in many eukaryotic genomes. Background The availability of bacterial genome .