title: Comparative genomics of the bacterial genus Streptococcus illuminates evolutionary implications of species groups.
abstract: Members of the genus Streptococcus within the phylum Firmicutes are among the most diverse and significant zoonotic pathogens. This genus has gone through considerable taxonomic revision due to increasing improvements of chemotaxonomic approaches, DNA hybridization and 16S rRNA gene sequencing. It is proposed to place the majority of streptococci into "species groups". However, the evolutionary implications of species groups are not clear presently. We use comparative genomic approaches to yield a better understanding of the evolution of Streptococcus through genome dynamics, population structure, phylogenies and virulence factor distribution of species groups. Genome dynamics analyses indicate that the pan-genome size increases with the addition of newly sequenced strains, while the core genome size decreases with sequential addition at the genus level and species group level. Population structure analysis reveals two distinct lineages, one including Pyogenic, Bovis, Mutans and Salivarius groups, and the other including Mitis, Anginosus and Unknown groups. Phylogenetic dendrograms show that species within the same species group cluster together, and infer two main clades in accordance with population structure analysis. Distribution of streptococcal virulence factors has no obvious patterns among the species groups; however, the evolution of some common virulence factors is congruous with the evolution of species groups, according to phylogenetic inference. We suggest that the proposed streptococcal species groups are reasonable from the viewpoints of comparative genomics; evolution of the genus is congruent with the individual evolutionary trajectories of different species groups.
authors: Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China; University of Chinese Academy of Sciences, Beijing, China.
authors: Xiao-Yang
authors: XY
authors: Gao
authors: Key Laboratory of Microbial Diversity in Southwest China, Ministry of Education and the Laboratory for Conservation and Utilization of Bio-Resources, Yunnan Institute of Microbiology, Yunnan University, Kunming, China.
authors: Xiao-Yang
authors: XY
authors: Zhi
authors: Key Laboratory of Microbial Diversity in Southwest China, Ministry of Education and the Laboratory for Conservation and Utilization of Bio-Resources, Yunnan Institute of Microbiology, Yunnan University, Kunming, China; The First Hospital of Qujing City, Qujing Affiliated Hospital of Kunming Medical University, Qujing, China.
authors: Hong-Wei
authors: HW
authors: Li
authors: Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany.
authors: Hans-Peter
authors: HP
authors: Klenk
authors: Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China; Key Laboratory of Microbial Diversity in Southwest China, Ministry of Education and the Laboratory for Conservation and Utilization of Bio-Resources, Yunnan Institute of Microbiology, Yunnan University, Kunming, China.
authors: Wen-Jun
authors: WJ
authors: Li
mesh_terms: D001482:Base Composition / Q000235:genetics; D005075:Biological Evolution; D017124:Conserved Sequence / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D059646:Genome Size / Q000235:genetics; D023281:Genomics; D010802:Phylogeny; D013045:Species Specificity; D013291:Streptococcus / Q000235:genetics*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors