Peptostreptococcus equinus sp. nov., isolated from horse faeces

Area of Science:

• Microbiology
• Bacteriology
• Genomics

Background:

• The genus *Peptostreptococcus* comprises anaerobic, Gram-positive bacteria found in various environments.
• Accurate classification of bacterial species is crucial for understanding microbial ecology and host-associated microbiomes.

Purpose of the Study:

• To characterize a novel bacterial isolate from horse feces.
• To determine the phylogenetic and taxonomic position of the novel isolate within the *Peptostreptococcus* genus.

Main Methods:

• Isolation and cultivation of anaerobic bacteria from horse fecal samples.
• 16S rRNA gene sequencing for phylogenetic analysis.
• Comparative genomic analysis, including DNA G+C content determination and digital DNA-DNA hybridization (dDDH).
• Phenotypic characterization, including cell morphology, Gram staining, spore formation, motility, and biochemical tests (catalase, oxidase).
• Fatty acid profiling.

Main Results:

• A novel Gram-positive, non-spore-forming, obligate anaerobic coccus, strain CBA3647^T, was isolated.
• Phylogenetic analysis based on 16S rRNA gene sequences placed strain CBA3647^T within the genus *Peptostreptococcus*, forming a distinct lineage.
• The highest 16S rRNA gene similarity was 98.31% with *Peptostreptococcus anaerobius* ATCC 27337^T; dDDH values were ≤24% with other *Peptostreptococcus* species.
• Genomic DNA G+C content was 30.0 mol%.
• Strain CBA3647^T exhibited optimal growth at 35°C, pH 7, and 1% NaCl, with major fatty acids C_14:0 iso and C_16:0.

Conclusions:

• Phenotypic, chemotaxonomic, and molecular data support the classification of strain CBA3647^T as a novel species within the genus *Peptostreptococcus*.
• The novel species is named *Peptostreptococcus equinus* sp. nov., with strain CBA3647^T as the type strain.