Shewanella oncorhynchi Sp. Nov., a Novel Member of the Genus Shewanella, Isolated from Rainbow Trout (Oncorhynchus mykiss)

Abstract

A strain, S-1(T) was isolated from rainbow trout (Oncorhynchus mykiss) exhibiting clinical symptoms of lens atrophy, inappetence, visual impairment and growth retardation. The strain was identified as representing a member of the genus Shewanella on the basis of the results of 16S rRNA gene sequence analysis. The neighbor-joining phylogenetic tree based on 16S rRNA gene sequences indicated that S-1(T) clustered with Shewanella putrefaciens JCM 20190(T), Shewanella profunda DSM 15900(T), and Shewanella hafniensis P010(T), sharing 99.3, 98.8 and 87.7% 16S rRNA gene similarities, respectively. A polyphasic taxonomic approach including phenotypic, chemotaxonomic, and genomic characterization was employed to ascertain the taxonomic position of S-1(T) within the genus Shewanella. The overall genome relatedness indices (OGRI) for S-1(T) compared with the most closely related type strains S. hafniensis ATCC BAA-1207(T), Shewanella baltica NCTC 10735(T), S. putrefaciens ATCC 8071(T) and S. profunda DSM 15900(T) were calculated as 40.8, 40.1, 28.5 and 27.3% for digital DNA-DNA hybridization (dDDH), and 91.6, 91.0, 86.3 and 85.1% for average nucleotide identity (ANI), respectively. OGRI values between S-1(T) and its close neighbours confirmed that the strain represents a novel species in the genus Shewanella. The DNA G+C content of the strain is 45.2%. Major fatty acids were C-17:1.8 omega 8c, C(15:0)iso, and summed feature 3 (C-16:1 omega 6c and/or C-16:1 omega 7c). The predominant polar lipids were phosphatidylethanolamine, phospholipid, amino-phospholipid and unidentified lipids. The major respiratory quinones were ubiquinone-8, ubiquinone-7 and menaquinone-7. Chemotaxonomic and phylogenomic analyses of this isolate confirmed that the strain represents a novel species for which the name Shewanella oncorhynchi sp. nov. is proposed, with S-1(T) as the type strain (JCM 34183(T)= KCTC 82249(T)).