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Outbreaks of diseases in farmed fish remain a recurring problem despite the development of vaccines and improved hygiene standards on aquaculture farms. One commonly observed bacterial disease in tropical aquaculture of the South-East Asian region is tenacibaculosis, which is attributed to members of the genus Tenacibaculum (family Flavobacteriaceae, phylum Bacteroidetes), most notably Tenacibaculum maritimum. The impact of tenacibaculosis on the fish microbiota remains poorly understood. In this study, we analysed the microbiota of different tissues of commercially reared Asian seabass (Lates calcarifer) that showed symptoms of tenacibaculosis and compared the microbial communities to those of healthy and experimentally infected fish that were exposed to diseased farmed fish. The relative abundance of Tenacibaculum species in experimentally infected fish was significantly lower than in commercially reared diseased fish and revealed a higher prevalence of different Tenacibaculum species. One isolated strain, TLL-A2 T , shares 98.7% 16S rRNA gene identity with Tenacibaculum mesophilum DSM 13764 T . The genome of strain TLL-A2 T was sequenced and compared to that of T. mesophilum DSM 13764 T . Analysis of average nucleotide identity and comparative genome analysis revealed only 92% identity between T. mesophilum DSM 13764 T and strain TLL-A2 T and differences between the two strains in predicted carbohydrate activating enzymes respectively. Phenotypic comparison between strain TLL-A2 T and T. mesophilum DSM 13764 T indicated additional differences, such as growth response at different salt concentrations. Based on molecular and phenotypic differences, strain TLL-A2 T (=DSM 106434 T , KCTC 62393 T ) is proposed as the type strain of Tenacibaculum singaporense sp. nov.

A novel Gram-stain negative, aerobic, non-flagellated, rod-shaped gliding bacterial strain, designated HFJ(T), was isolated from a skin lesion of a diseased Atlantic salmon (Salmo salar L.) in Finnmark, Norway. Colonies were observed to be yellow pigmented with entire and/or undulating margins and did not adhere to the agar. The 16S rRNA gene sequence showed that the strain belongs to the genus Tenacibaculum (family Flavobacteriaceae, phylum 'Bacteroidetes'). Strain HFJ(T) exhibits high 16S rRNA gene sequence similarity values to Tenacibaculum dicentrarchi NCIMB 14598(T) (97.2 %). The strain was found to grow at 2-20 °C and only in the presence of sea salts. The respiratory quinone was identified as menaquinone 6 and the major fatty acids were identified as summed feature 3 (comprising C16:1 ω7c and/or iso-C15:0 2-OH), iso-C15:0, anteiso-C15:0, iso-C15:1 and iso-C15:0 3-OH. The DNA G+C content was determined to be 34.1 mol%. DNA-DNA hybridization and comparative phenotypic and genetic tests were performed with the phylogenetically closely related type strains, T. dicentrarchi NCIMB 14598(T) and Tenacibaculum ovolyticum NCIMB 13127(T). These data, as well as phylogenetic analyses, suggest that strain HFJ(T) should be classified as a representative of a novel species in the genus Tenacibaculum, for which the name Tenacibaculum finnmarkense sp. nov. is proposed; the type strain is HFJ (T) = (DSM 28541(T) = NCIMB 42386(T)).

A Gram-stain-negative, non-spore-forming, aerobic, non-flagellated, gliding and rod-shaped bacterial strain, designated HJ-26M(T), was isolated from a tidal flat sediment in the Korean peninsula. It grew optimally at 25-30 °C, at pH 7.0-8.0 and in the presence of 2 % (w/v) NaCl. A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences revealed that the strain fell within the clade comprising Tenacibaculum species, clustering coherently with the type strains of Tenacibaculum lutimaris and Tenacibaculum aestuarii. Strain HJ-26M(T) exhibited the highest 16S rRNA gene sequence similarity values of 98.4 and 98.2 % to T. lutimaris TF-26(T) and T. aestuarii SMK-4(T), respectively, and of 94.9-97.4 % to the type strains of the other Tenacibaculum species. Strain HJ-26M(T) contained MK-6 as the predominant menaquinone and iso-C15:0 and iso-C17:0 3-OH as the major fatty acids. The DNA G+C content of strain HJ-26M(T) was 34.5 mol% and its mean DNA-DNA relatedness values with the type strains of T. lutimaris and T. aestuarii were 19 and 23 %, respectively. Differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that strain HJ-26M(T) is separate from other Tenacibaculum species. On the basis of the data presented, strain HJ-26M(T) is considered to represent a novel species of the genus Tenacibaculum, for which the name Tenacibaculum caenipelagi sp. nov. is proposed. The type strain is HJ-26M(T) (= KCTC 32323(T) = CECT 8283(T)).

A Gram-negative, non-spore-forming, aerobic, non-flagellated, non-gliding and rod-shaped bacterial strain, designated P-R2A1-2(T), was isolated from sea squirt (Halocynthia roretzi) collected from the South Sea, Korea. It grew optimally at 25-28 °C, at pH 7.0-8.0 and in the presence of 2 % (w/v) NaCl. Neighbour-joining phylogenetic tree based on 16S rRNA gene sequences revealed that the strain fell within the clade comprising Tenacibaculum species. Strain P-R2A1-2(T) exhibited the highest 16S rRNA gene sequence similarity values of 97.6, 97.2 and 97.0 % to Tenacibaculum aestuarii SMK-4(T), T. lutimaris TF-26(T) and T. aiptasiae a4(T), respectively, and of 94.5-96.8 % to the type strains of the other Tenacibaculum species. Strain P-R2A1-2(T) contained MK-6 as the predominant menaquinone and C16:1 ω7c and/or iso-C15:0 2-OH, iso-C15:0 3-OH and iso-C15:0 as the major fatty acids. The DNA G + C content of strain P-R2A1-2(T) was 30.7 mol % and its DNA-DNA relatedness values with the type strains of T. aestuarii, T. lutimaris and T. aiptasiae were 17 ± 4.2, 21 ± 6.1 and 16 ± 5.2 %, respectively. Differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that the novel strain is separate from other Tenacibaculum species. On the basis of the data presented, strain P-R2A1-2(T) is considered to represent a novel species of the genus Tenacibaculum, for which the name Tenacibaculum halocynthiae sp. nov. is proposed. The type strain is P-R2A1-2(T) (=KCTC 32262(T )= CCUG 63681(T)).