Actinomyces ruminis sp. nov., an obligately anaerobic bacterium isolated from the rumen of cattle

Abstract

An obligately anaerobic, rod-shaped, Gram-stain-positive, non-spore-forming, non-motile bacterial strain; designated as CtC72^T was isolated from the rumen of cattle. The 16S rRNA gene sequence similarity of less than 98.65% revealed the strain as a member of the genus Actinomyces, nearest to but distinct from Actinomyces qiguomingii DSM 106201^T, Actinomyces ruminicola DSM 27982^T, Actinomyces procaprae JCM 33484^T, Actinomyces succiniciruminis TISTR 2317, Actinomyces glycerinitolerans TISTR 2318. The low values of digital DNA-DNA hybridization (< 70%) and average nucleotide identity (< 95%) further highlighted the distinctive nature of strain CtC72^T from its closest relatives. The strain CtC72^T could grow at temperatures between 30 and 50 °C (optimum 40 °C), pH between 6.0 and 9.0 (optimum 7.5-8.0), and NaCl between 0 and 1.5% (optimum 0%). The strain hydrolysed cellulose and xylan and utilised a range of mono-, di-, and oligo-saccharides as a source of carbon and energy. Glucose fermentation resulted in acetic acid and formic acid as major metabolic products, while propionic acid, lactic acid, and ethanol as minor products along with CO₂ production. The DNA G + C content of strain CtC72^T was 68.40 (mol%, T_m) and 68.05 (%, digital). Major cellular fatty acids (> 10%) were C_16:0, C_18:1 ω9c_, and C_18:1 ω9c DMA. Based on these data, we propose that strain CtC72^T be classified as a novel species, Actinomyces ruminis sp. nov., under the genus Actinomyces. The type strain is CtC72^T (= KCTC 15726^T = JCM 32641^T = MCC 3500^T).

Keywords: Anaerobes; Diversity; Fibre degradation; Herbivores; Phylogeny; Ruminants; Taxonomy.