Genomic and phenotypic characterization of Streptococcus intestinihominis sp. nov. from the human intestinal tract.

A novel α-haemolytic bacterial strain, IMAU11619T, belonging to the genus Streptococcus, was isolated from human intestinal tract samples collected in Hohhot City, Inner Mongolia Autonomous Region of China. Strain IMAU11619T is characterized as Gram-positive, non-motile, non-spore-forming cocci. Optimal growth conditions were anaerobically determined at 37 °C and pH 6 in De Man-Rogosa-Sharpe medium. We sequenced the draft genome of strain IMAU11619T and characterized its taxonomic status using phylogenetic and phenotypic analyses. Comparative analysis with the TYGS database indicated that strain IMAU11619T represents a novel species within the genus Streptococcus that is phylogenetically distinct from all previously characterized species. Phylogenetic reconstruction based on 176 single-copy genes positioned this strain within the parasanguinis subclade of the Mitis-Suis clade and closely related to Streptococcus rubneri DSM 26920T, Streptococcus australis ATCC 700641T and Streptococcus ilei I-G2T. The highest observed average nucleotide identity and digital DNA-DNA hybridization values with its closest relative, S. australis ATCC 700641T, were 93.1-93.8 and 52.8%, respectively. The genomic DNA G+C content of strain IMAU11619T was 42.2 mol%. The major fatty acid components identified included C16:0, C14:1, C18:0 and summed feature 8 (C18:1  ω7c and/or C18:1  ω6c). The respiratory quinone type of strain IMAU11619T was identified as menaquinone-9. Based on its distinctive phylogenetic position and phenotypic features, strain IMAU11619T is proposed as a novel species, Streptococcus intestinihominis sp. nov., with type strain IMAU11619T (=CGMCC 1.64731T=GDMCC 1.4355T=JCM 37062T).