New bacterial species isolated from a Helicobacter pylori-positive pre-neoplastic human stomach

A facultative anaerobic, catalase-negative, lactic acid-producing, non-endospore-forming, Gram-positive coccoid bacterium, strain MT/JULY 2010^T, was isolated from the stomach of a Helicobacter pylori-positive Japanese female patient with pre-neoplastic gastric mucosa. This bacterium can form clusters, chains, or pairs, or occurs singly in liquid media. The growth ranges for temperature, pH and NaCl concentration were 20–45 °C, pH 5.0–7.0, and 1–4%, respectively. 

When an Osaka Metropolitan University-led research team observed the cells under the microscope using a hanging drop assay, they exhibited an unusual tumbling motion. Observation under an electron microscope showed some unidentified structures and numerous fimbriae-like appendages. 

The combined results of 16S rRNA gene sequence analysis and the overall genome-related index, average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH), classified the bacterium as a novel species of the genus Streptococcus. It forms a monophyletic cluster with Streptococcus parasanguinis ATCC 15912^T in the phylogenetic tree with 94.4% ANI. Furthermore, the conventional DNA–DNA hybridization assay and dDDH of the two strains identified their relatedness as 62.5% and 58.7% (both below the 70% threshold), respectively. The DNA G+C content, determined by nuclease P1-digested genomic DNA, was 42.6 mol%, while the digital G+C content calculated in silico was 41.8 mol%. Based on the phenotypic and genotypic results, strain MT/JULY 2010^T represents a novel species within the genus. The name Streptococcus mobilis sp. nov. is proposed. The type strain is MT/JULY 2010^T. 

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