Peptoniphilus equinus sp. nov., a novel Gram-stain-positive anaerobic coccus isolated from the faeces of a thoroughbred racehorse.

The research deals with the identification and characterization of a new bacterial strain, Peptoniphilus equinus sp. nov., discovered in the faeces of a racehorse. This strain shows unique genetic, physical, and biochemical features, distinguishing it from other known species of the Peptoniphilus genus.

Isolation and Preliminary Identification

• The group isolated a new bacterial strain, named CBA3646, from the feces of a thoroughbred racehorse.
• The coccus-shaped bacteria were gram-positive and anaerobic, meaning they could thrive in environments without oxygen.
• Initial phylogenetic analysis, based on the 16S rRNA gene (a common method used for species differentiation), demonstrated that CBA3646 closely related to the Peptoniphilus genus.

Physical and Biochemical Properties

• The cells were identified as diplococci, occurring in pairs, and were non-motile.
• They tested positive for catalase – an enzyme that breaks down harmful hydrogen peroxide into oxygen and water – but didn’t exhibit any oxidase activity.
• CBA3646 showed growth at temperatures between 20-40°C and could survive in the presence of 0-4% weight/volume sodium chloride, with optimum temperature and salt concentration being 35°C and 1% respectively.
• The predominant cellular fatty acids were C15:0, C16:0ω9 and C18:1ω9 dimethyl acetal while major polar lipids included diphosphatidylglycerol and phosphatidylglycerol.

Genetic Analysis

• CBA3646’s genomic features were analyzed and it was found to have a circular chromosomal genome of 1 709 189 base pairs with a DNA G+C (guanine-cytosine) content of 45.5%.
• The genome contained 1652 genes, of which 1584 were predicted to be protein-coding genes. Additionally, there were 3 complete rRNA loci and 47 tRNA genes.
• The DNA-DNA relatedness and average nucleotide identity values between CBA3646 and its closest relative, DSM 20463, were found to be only 21.4% and 67.6% respectively, proving a significant difference between the two.

Conclusion

• Meticulous exploration of the bacterial strain’s phylogenetic, physiological, chemotaxonomic, and genetic details led researchers to conclude that CBA3646 represents a novel species within the Peptoniphilus genus.
• The newly identified species was proposed to be named Peptoniphilus equinus sp. nov., with CBA3646 serving as the type strain.