Cutibacterium equinum sp. nov., isolated from horse faeces.

Overview

• Researchers identified and characterized a new bacterial species isolated from horse feces on Jeju Island, Korea.
• This novel bacterium belongs to the genus Cutibacterium and has unique genetic and biochemical traits that distinguish it from known species.

Introduction and Isolation

• The bacterium, designated strain CBA3108, was obtained from horse fecal samples collected in Jeju Island, Republic of Korea.
• It is an obligately anaerobic microorganism, meaning it requires an oxygen-free environment for growth.

Cellular Characteristics

• CBA3108 cells are Gram-positive, indicating a thick peptidoglycan layer in the bacterial cell wall.
• The cells are non-motile short rods and do not form spores, which are protective structures some bacteria produce.
• The strain tests catalase-positive, meaning it produces the enzyme catalase, and oxidase-negative, indicating it lacks certain cytochrome c oxidases.

Growth Conditions

• Temperature range for growth: 25-45°C, with an optimum at 35°C.
• pH range: 6 to 9, with optimal growth at pH 6.
• Salt tolerance: grows in 0-6% (weight/volume) NaCl, optimally around 2% NaCl concentration.

Chemical Composition

• Major fatty acids identified include isomers of C iso and C iso DMA (dimethyl acetal), which are characteristic components of bacterial membranes.
• Major polar lipids detected were phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylcholine—important components of cellular membranes.

Phylogenetic Analysis

• 16S rRNA gene sequencing was used to analyze the phylogenetic position of strain CBA3108 within the genus Cutibacterium.
• The strain forms a distinct lineage separate from its closest relatives, demonstrating sufficient genetic difference for designation as a new species.
• The closest known species showed 98.27% similarity in the 16S rRNA gene sequence, which is below the usual threshold for species identity, supporting novelty.

Genomic and Molecular Properties

• The genomic DNA guanine-plus-cytosine (G+C) content of CBA3108 is 63.2 mol%, which is a useful taxonomic characteristic.
• DNA-DNA hybridization (DDH) values between CBA3108 and related strains ranged from about 21.7% to 33.6% — well below the 70% threshold generally used to define bacterial species.

Conclusion and Species Proposal

• Based on phenotypic (observable traits), chemotaxonomic (chemical composition), and molecular (genetic) evidence, strain CBA3108 represents a novel species within the genus Cutibacterium.
• The proposed name for this new species is Cutibacterium equinum sp. nov., indicating its origin from horses (“equinum” meaning pertaining to horses).
• The type strain for this new species is CBA3108, deposited in culture collections with accession numbers KACC 22889 and JCM 35966.