# Streptococcus mobilis sp. nov., isolated from a Helicobacter pylori-positive pre-neoplastic human stomach

## TL;DR

A new species of Streptococcus, named S. mobilis, was discovered in the stomach of a patient with pre-cancerous changes linked to Helicobacter pylori.

## Contribution

Identification of a novel Streptococcus species associated with pre-neoplastic gastric conditions.

## Key findings

- Strain MT/JULY 2010T forms a distinct monophyletic cluster with S. parasanguinis but is below the species threshold for relatedness.
- The bacterium exhibits unique motility and morphology, including fimbriae-like appendages and a tumbling motion.
- Genomic and phenotypic analyses confirm it as a new species within the genus Streptococcus.

## Abstract

A facultative anaerobic, catalase-negative, lactic acid-producing, non-endospore-forming, Gram-positive coccoid bacterium, strain MT/JULY 2010T, 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. Cells exhibited an unusual tumbling motion when observed under the microscope using a hanging drop assay. 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 15912T 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 2010T represents a novel species within the genus. The name Streptococcus mobilis sp. nov. is proposed. The type strain is MT/JULY 2010T (=ATCC BAA-2258T=NBRC 107862T=NCBI 948105T=V10/022878T).