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.
Highlights
The genus Streptococcus comprises a wide variety of pathogenic and commensal gram-positive bacteria [1]
The analyses enabled us to test (1) pan-genome size and core genome size of Streptococcus and species groups; (2) the phylogenetic relationships among those groups based on genomic data; (3) the reasonableness of species groups raised by associated biochemical features and 16S rRNA gene analysis; and (4) distribution of virulence factor among species groups, in order to explore their implications in evolution of the genus
Applications of chemotaxonomic approaches, DNA hybridization and 16S rRNA gene sequencing have resulted in the proposal of ‘‘species groups’’ for streptococci with various lifestyles
Summary
The genus Streptococcus comprises a wide variety of pathogenic and commensal gram-positive bacteria [1]. Recent applications of chemotaxonomic approaches, genomic DNA-DNA hybridization and 16S rRNA sequencing techniques have provided significant insights into the natural relationships among streptococci, but have influenced significantly their taxonomy and nomenclature [10,11,12,13] These revisions form the basis of delineation and reveal the natural grouping of species into ‘‘species groups’’ [14]. The species groups have been named ‘‘Pyogenic’’, ‘‘Mitis’’, ‘‘Anginosus’’, ‘‘Bovis’’, ‘‘Mutans’’ and ‘‘Salivarius’’ respectively, and they encompass the majority of described species (several species remain ungrouped) These polyphasic taxonomy approaches are still widely used in many laboratories, limits of biochemical determination, and low efficiency operation of DNA hybridization [15] as well as possible phenotypic and ecological differentiation underlying identical 16S rRNA genes [16] all inevitably hamper the evolutionary and taxonomic investigations of streptococci.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.