Abstract
Strain P3-BQ1(T) is a Gram-negative, aerobic, non-spore-forming bacterium with gliding motility and filamentous cells. It was isolated in 2018 from the gills of a diseased Atlantic salmon (Salmo salar) during an outbreak of tenacibaculosis in a Chilean fish farm. Phylogenetic analysis based on 16S rRNA gene sequencing confirmed that strain P3-BQ1(T) belongs to the genus Tenacibaculum and is most closely related to Tenacibaculum dicentrarchi 35/09(T) (98.53%), 'Tenacibaculum pacificus' 18-2881-A (98.46%), Tenacibaculum aestuariivivum JDTF-79(T) (98.46%), Tenacibaculum finnmarkense TNO010 (97.85%) and Tenacibaculum piscium TNO20(T) (97.41%). The genome size of strain P3-BQ1(T) is 2,777,603 bp, with a DNA G+C content of 29.18 mol%. The strain has an OrthoANI score lower than 95% compared to the types of all validly named Tenacibaculum species, with the closest neighbour being T. dicentrarchi 35/09(T) (score 87.41 %). In contrast, P3-BQ1ᵀ and 'T. pacificus' 18-2881-A shared a 96.58%, thus exceeding the species threshold. This result is also supported by whole-genome in silico DNA-DNA hybridization/Genome-to-Genome Distance Calculator values, indicating that strains P3-BQ1(T) and 18-2881-A are conspecific. Strain P3-BQ1(T) contains MK-6 as its sole detectable menaquinone. The polar lipids profile includes glycolipids (n=2), aminolipids (n=3) and unidentified lipids (n=5). The predominant cellular fatty acids (>5 %) are C(13 : 1), C(15 : 0), iso-C(15 : 0), iso-C(15 : 0) 3-OH and summed feature 3 (C(16 : 1)ω7с/C(16 : 1)ω6с). An immersion challenge was conducted to assess the pathogenic potential in Atlantic salmon. Our findings indicate that strain P3-BQ1(T) alone does not cause significant mortality, suggesting it is likely non-pathogenic to this species. Based on the phenotypic, phylogenetic and genotypic data presented, Tenacibaculum salmonis sp. nov. is proposed here with type strain P3-BQ1(T) (=IMI 507635(T)=RGM 3581(T)), being 18-2881-A an additional strain.