tailieunhanh - Báo cáo y học: "Evolution of the core and pan-genome of Streptococcus: positive selection, recombination, and genome composition"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Critical Care giúp cho các bạn có thêm kiến thức về ngành y học đề tài: Evolution of the core and pan-genome of Streptococcus: positive selection, recombination, and genome composition. | Research Open Access Evolution of the core and pan-genome of Streptococcus positive selection recombination and genome composition Tristan Lefebure and Michael J Stanhope Address Department of Population Medicine and Diagnostic Sciences College of Veterinary Medicine Cornell University Ithaca NY 14853 USA. Correspondence Michael J Stanhope. Email mjs297@ Published 2 May 2007 Genome Biology 2007 8 R71 doi 186 gb-2007-8-5-r71 The electronic version of this article is the complete one and can be found online at http 2007 8 5 R71 Received 28 November 2006 Revised 24 April 2007 Accepted 2 May 2007 2007 Lefébure and Stanhope licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License http licenses by which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. Abstract Background The genus Streptococcus is one of the most diverse and important human and agricultural pathogens. This study employs comparative evolutionary analyses of 26 Streptococcus genomes to yield an improved understanding of the relative roles of recombination and positive selection in pathogen adaptation to their hosts. Results Streptococcus genomes exhibit extreme levels of evolutionary plasticity with high levels of gene gain and loss during species and strain evolution. S. agalactiae has a large pan-genome with little recombination in its core-genome while S. pyogenes has a smaller pan-genome and much more recombination of its core-genome perhaps reflecting the greater habitat and gene pool diversity for S. agalactiae compared to S. pyogenes. Core-genome recombination was evident in all lineages 18 to 37 of the core-genome judged to be recombinant while positive selection was mainly observed during species differentiation from 11 to 34 of the core-genome . Positive selection pressure was unevenly distributed .