Flavobacterium turcicum sp. nov. and Flavobacterium kayseriense sp. nov. isolated from farmed rainbow trout in Turkey

Specific amino acid changes correlate with pathogenic flavobacteria

Flavobacterium is a genus of microorganisms living in a variety of hosts and habitats across the globe. Some species are found in fish organs, and only a few, such as Flavobacterium psychrophilum and Flavobacterium columnare, cause severe disease and losses in fish farms. The evolution of flavobacteria that are pathogenic to fish is unknown, and the protein changes accountable for the selection of their colonization to fish have yet to be determined. A phylogenetic tree was constructed with the complete genomic sequences of 208 species of the Flavobacterium genus using 861 softcore genes. This phylogenetic analysis revealed clade CII comprising nine species, including five pathogenic species, and containing the most species that colonize fish. Thirteen specific amino acid changes were found to be conserved across 11 proteins within the CII clade compared with other clades, and these proteins were enriched in functions related to replication, recombination, and repair. Several of these proteins are known to be involved in pathogenicity and fitness adaptation in other bacteria. Some of the observed amino acid changes can be explained by preferential selection for certain codons and tRNA frequency. These results could help explain how species belonging to the CII clade adapt to fish environments.

Comprehensive genome analysis of five novel flavobacteria: Flavobacterium piscisymbiosum sp. nov., Flavobacterium pisciphilum sp. nov., Flavobacterium flavipigmentatum sp. nov., Flavobacterium lipolyticum sp. nov. and Flavobacterium cupriresistens sp. nov

Eight isolates were obtained through a study on culture-dependent bacteria from fish farms and identified as members of the genus Flavobacterium based on pairwise analysis of the 16S rRNA gene sequences. The highest pairwise identity values were calculated as 98.8 % for strain F-30 T and Flavobacterium bizetiae, 99.0 % for strain F-65 T and Flavobacterium branchiarum, 98.7 % for strain F-126 T and Flavobacterium tructae, 98.2 % for strain F-323 T and Flavobacterium cupreum while 99.7 % identity level was detected for strain F-70 T and Flavobacterium geliluteum. In addition, strains F-33, Fl-77, and F-70 T shared 100 % identical 16S rRNA genes, while strains F-323 T and Fl-318 showed 99.9 % identity. A polyphasic approach including comparative analysis of whole-genome data was employed to ascertain the taxonomic provenance of the strains. In addition to the morphological, physiological, biochemical and chemotaxonomic characteristics of the strains, the overall genome-relatedness indices of dDDH and ANI below the established thresholds confirmed the classification of the strains as five novel species within the genus Flavobacterium. The comprehensive genome analyses of the strains were also conducted to determine the biosynthetic gene clusters, virulence features and ecological distribution patterns. Based on the polyphasic characterisations, including comparative genome analyses, it is concluded that strains F-30 T, F-65 T, F-70 T, F126T and F-323 T represent five novel species within the genus Flavobacterium for which Flavobacterium piscisymbiosum sp. nov. F-30 T (=JCM 34194 T = KCTC 82254 T), Flavobacterium pisciphilum sp. nov. F-65 T (=JCM 34197 T = KCTC 82257 T), Flavobacterium flavipigmentatum sp. nov. F-70 T (Fl-33 = Fl-77 = JCM 34198 T = KCTC 82258 T), Flavobacterium lipolyticum sp. nov. F-126 T (JCM 34199 T = KCTC 82259 T) and Flavobacterium cupriresistens sp. nov. F-323 T (Fl-318 = JCM 34200 T = KCTC 82260 T), are proposed.

A review of bacterial disease outbreaks in rainbow trout (Oncorhynchus mykiss) reported from 2010 to 2022

Outbreaks of bacterial infections in aquaculture have emerged as significant threats to the sustainable production of rainbow trout (Oncorhynchus mykiss) worldwide. Understanding the dynamics of these outbreaks and the bacteria involved is crucial for implementing effective management strategies. This comprehensive review presents an update on outbreaks of bacteria isolated from rainbow trout reported between 2010 and 2022. A systematic literature survey was conducted to identify relevant studies reporting bacterial outbreaks in rainbow trout during the specified time frame. More than 150 published studies in PubMed, Web of Science, Scopus, Google Scholar and relevant databases met the inclusion criteria, encompassing diverse geographical regions and aquaculture systems. The main bacterial pathogens implicated in the outbreaks belong to both gram-negative, namely Chryseobacterium, Citrobacter, Deefgea Flavobacterium, Janthinobacterium, Plesiomonas, Pseudomonas, Shewanella, and gram-positive genera, including Lactococcus and Weissella, and comprise 36 new emerging species that are presented by means of pathogenicity and disturbance worldwide. We highlight the main characteristics of species to shed light on potential challenges in treatment strategies. Moreover, we investigate the role of various risk factors in the outbreaks, such as environmental conditions, fish density, water quality, and stressors that potentially cause outbreaks of these species. Insights into the temporal and spatial patterns of bacterial outbreaks in rainbow trout aquaculture are provided. Furthermore, the implications of these findings for developing sustainable and targeted disease prevention and control measures are discussed. The presented study serves as a comprehensive update on the state of bacterial outbreaks in rainbow trout aquaculture, emphasizing the importance of continued surveillance and research to sustain the health and productivity of this economically valuable species.

Genomic insight into Myroides oncorhynchi sp. nov., a new member of the Myroides genus, isolated from the internal organ of rainbow trout (Oncorhynchus mykiss)

The strain M-43^T was isolated from the Oncorhynchus mykiss from a fish farm in Mugla, Turkey. Pairwise 16S rRNA gene sequence analysis was used to identify strain M-43^T. The strain was a member of the genus Myroides sharing the highest 16S rRNA gene sequence identity levels of 98.7%, 98.3%, and 98.3% with the type strains of M. profundi D25^T, M. odoratimimus subsp. odoratimimus CCUG 39352^T and M. odoratimimus subsp. xuanwuensis DSM27251^T, respectively. A polyphasic taxonomic approach including whole genome-based analyses was employed to confirm the taxonomic provenance of strain M-43^T within the genus Myroides. The overall genome relatedness indices (OGRI) for strain M-43^T compared with its most closely related type strains M. odoratimimus subsp. xuanwuensis DSM 27251^T, M. profundi D25^T, and M. odoratimimus subsp. odoratimimus ATCC BAA-634^T, were calculated as 25.3%, 25.1%, and 25% for digital DNA-DNA hybridization (dDDH), 83.3%, 83.6%, and 83.4% for average nucleotide identity (ANI) analyses, respectively. The OGRI values between strain M-43^T and its close neighbors confirmed that the strain represents a novel species in the genus Myroides. The DNA G + C content of the strain is 33.7%. The major fatty acids are iso-C_15:0 and summed feature 9 (iso-C_17:1 ω9c and/or 10-methyl C_16:0). The predominant polar lipids are phosphatidylethanolamine, an amino-lipid and five unidentified lipids. The major respiratory quinone is MK-6. Chemotaxonomic and phylogenomic analyses of this isolate confirmed that the strain represents a novel species for which the name Myroides oncorhynchi sp. nov. is proposed, with M-43^T as the type strain (JCM 34205^T = KCTC 82265^T).

An Update on Novel Taxa and Revised Taxonomic Status of Bacteria (Including Members of the Phylum Planctomycetota) Isolated from Aquatic Host Species Described in 2018 to 2021

Increased interest in farmed aquatic species, aquatic conservation measures, and microbial metabolic end-product utilization have translated into a need for awareness and recognition of novel microbial species and revisions to bacterial taxonomy. Because this need has largely been unmet, through a 4-year literature review, we present lists of novel and revised bacterial species (including members of the phylum Planctomycetota) derived from aquatic hosts that can serve as a baseline for future biennial summaries of taxonomic revisions in this field. Most new and revised taxa were noted within oxidase-positive and/or nonglucose fermentative Gram-negative bacilli, including members of the Tenacibaculum, Flavobacterium, and Vibrio genera. Valid and effectively published novel members of the Streptococcus, Erysipelothrix, and Photobacterium genera are additionally described from disease pathogenesis perspectives.

Atypical flavobacteria recovered from diseased fish in the Western United States

Flavobacterial diseases, caused by bacteria in the order Flavobacteriales, are responsible for devastating losses in farmed and wild fish populations worldwide. The genera Flavobacterium (Family Flavobacteriaceae) and Chryseobacterium (Weeksellaceae) encompass the most well-known agents of fish disease in the order, but the full extent of piscine-pathogenic species within these diverse groups is unresolved, and likely underappreciated. To identify emerging agents of flavobacterial disease in US aquaculture, 183 presumptive Flavobacterium and Chryseobacterium isolates were collected from clinically affected fish representing 19 host types, from across six western states. Isolates were characterized by 16S rRNA gene sequencing and phylogenetic analysis using the gyrB gene. Antimicrobial susceptibility profiles were compared between representatives from each major phylogenetic clade. Of the isolates, 52 were identified as Chryseobacterium species and 131 as Flavobacterium. The majority of Chryseobacterium isolates fell into six clades (A-F) consisting of ≥ 5 fish isolates with ≥ 70% bootstrap support, and Flavobacterium into nine (A-I). Phylogenetic clades showed distinct patterns in antimicrobial susceptibility. Two Chryseobacterium clades (F & G), and four Flavobacterium clades (B, G-I) had comparably high minimal inhibitory concentrations (MICs) for 11/18 antimicrobials tested. Multiple clades in both genera exhibited MICs surpassing the established F. psychrophilum breakpoints for oxytetracycline and florfenicol, indicating potential resistance to two of the three antimicrobials approved for use in finfish aquaculture. Further work to investigate the virulence and antigenic diversity of these genetic groups will improve our understanding of flavobacterial disease, with applications for treatment and vaccination strategies.

Shewanella oncorhynchi sp. nov., a novel member of the genus Shewanella, isolated from Rainbow Trout (Oncorhynchus mykiss)

A strain, S-1T 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-1T clustered with Shewanella putrefaciens JCM 20190T, Shewanella profunda DSM 15900T, and Shewanella hafniensis P010T, 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-1T within the genus Shewanella . The overall genome relatedness indices (OGRI) for S-1T compared with the most closely related type strains S. hafniensis ATCC BAA-1207T, Shewanella baltica NCTC 10735T, S. putrefaciens ATCC 8071T and S. profunda DSM 15900T 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-1T 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 C17 : 1ω8c, C15 : 0iso, and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c). 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-1T as the type strain (JCM 34183T= KCTC 82249T).

Helicobacter turcicus sp. nov., a catalase-negative new member of the Helicobacter genus, isolated from Anatolian Ground Squirrel (Spermophilus xanthoprymnus) in Turkey

Eleven Gram-negative, curved and S-shaped, oxidase activity positive, catalase activity negative bacterial isolates recovered from faeces of Anatolian ground squirrel (Spermophilus xanthoprymnus) in the city of Kayseri, Turkey, were subjected to a polyphasic taxonomic study. Results of a genus-specific PCR revealed that these isolates belonged to the genus Helicobacter . The 16S rRNA gene sequence analysis revealed that the 11 isolates had over 99 % sequence identity with each other and were most closely related to Helicobacter ganmani CMRI H02T with 97.0–97.1 % identity levels and they formed a novel phylogenetic line within the genus Helicobacter . Faydin-H64 and Faydin-H70T strains were subjected to gyrA and atpA gene and whole genome sequence analyses. These two Helicobacter strains formed separate phylogenetic clades, divergent from other known Helicobacter species. The DNA G+C content and genome size of the strain Faydin-H70T were 35.3 mol% and 1.7 Mb, respectively. Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between strain Faydin-H70T and its close phylogenetic neighbour H. winghamensis ATCC BAA-430T were determined as 81.7 and 34.9 %, respectively. Pairwise sequence comparison showed that it was closely related to H. ganmani CMRI H02T however it shared the highest ANI and dDDH values with H. winghamensis ATCC BAA-430T. The data obtained from the polyphasic taxonomy approach, including phenotypic characterization and whole-genome sequences, revealed that these strains represent a novel species within the genus Helicobacter , for which the name Helicobacter turcicus sp. nov., is proposed with Faydin-H70T as the type strain (=DSM 112556T=LMG 32335T).

Flavobacterium erciyesense sp. nov., a putative non-pathogenic fish symbiont

During a study aiming at isolation and genomic characterization of non-pathogenic fish symbionts, strain F-328^T was isolated from skin mucus of healthy-seeming rainbow trout (Oncorhynchus mykiss) and subjected to polyphasic characterization, including a comprehensive genome analysis. Strain F-328^T was Gram stain negative, none-gliding, strictly aerobic, and rod shaped. The 16S rRNA gene sequence of strain F-328^T exhibited the highest level of identity (98.9%) with F. turcicum F-339^T. The major fatty acids were iso-C_15:0, C_15:1 ω6c, and summed feature 3 (C_16:1 ω7c, C_16:1 ω6c). The polar lipid profile consisted mainly of phosphatidylethanolamine and aminolipids, while the predominant menaquinone was MK-6. The DNA G + C content and genome size of the strain were 35.3% and 3.4 Mb, respectively. Strain F-328^T shows 93.8% average nucleotide identity and 53% digital DNA-DNA hybridization identity with the closest type strain F. turcicum F-339^T. In addition, strain F-328^T was found to carry antimicrobial resistance genes, which confer resistance to several antimicrobials, including aminoglycoside, macrolides, and streptogramin. Differential phenotypic properties, together with the phylogenetic inference, demonstrate that strain F-328^T should be classified as a novel species of the genus Flavobacterium for which the name Flavobacterium erciyesense sp. nov. is proposed, with F-328^T as the type strain (= JCM 34201^T = KCTC 82261^T).

Genetic Characterization of the Tetracycline-Resistance Gene tet(X) Carried by Two Epilithonimonas Strains Isolated from Farmed Diseased Rainbow Trout, Oncorhynchus mykiss in Chile

The main objective of this study was to characterize the tet(X) genes, which encode a monooxygenase that catalyzes the degradation of tetracycline antibiotics, carried by the resistant strains FP105 and FP233-J200, using whole-genome sequencing analysis. The isolates were recovered from fin lesion and kidney samples of diseased rainbow trout Oncorhynchus mykiss, during two Flavobacteriosis outbreaks occurring in freshwater farms located in Southern Chile. The strains were identified as Epilithonimonas spp. by using biochemical tests and by genome comparison analysis using the PATRIC bioinformatics platform and exhibited a minimum inhibitory concentration (MIC) of oxytetracycline of 128 µg/mL. The tet(X) genes were located on small contigs of the FP105 and FP233-J200 genomes. The sequences obtained for the tet(X) genes and their genetic environment were compared with the genomes available in the GenBank database of strains of the Chryseobacterium clade belonging to the Flavobacterium family, isolated from fish and carrying the tet(X) gene. The Tet(X) proteins synthesized by the Chilean Epilithonimonas strains showed a high amino acid similarity (range from 84% to 100%), with the available sequences found in strains belonging to the genus Chryseobacterium and Flavobacterium isolated from fish. An identical neighborhood of tet(X) genes from both Chilean strains was observed. The genetic environment of tet(X) observed in the two strains of Epilithonimonas studied was characterized by the upstream location of a sequence encoding a hypothetical protein and a downstream located alpha/beta hydrolase-encoding gene, similar to the observed in some of the tet(X) genes carried by Chryseobacterium and Flavobacterium strains isolated from fish, but the produced proteins exhibited a low amino acid identity (25–27%) when compared to these synthesized by the Chilean strains. This study reports for the first time the carriage of the tet(X) gene by the Epilithonimonas genus and their detection in fish pathogenic bacteria isolated from farmed salmonids in Chile, thus limiting the use of therapies based on oxytetracycline, the antimicrobial most widely used in Chilean freshwater salmonid farming. This results suggest that pathogenic strains of the Chryseobacterium clade occurring in Chilean salmonid farms may serve as important reservoirs of tet(X) genes.

Flavobacterium muglaense sp. nov. isolated from internal organs of apparently healthy rainbow trout

Two yellow-pigmented isolates, F-60^T and F-392, were isolated from the internal organs of an apparently healthy rainbow trout (Oncorhynchus mykiss). The strains were identified as members of the genus Flavobacterium based on the results of 16S rRNA gene sequence analysis. Strains F-60^T and F-392 had the highest 16S rRNA gene sequence identity level of 97.4 % to the type strain of Flavobacterium crassostreae LPB0076^T. A polyphasic taxonomic approach including phenotypic, chemotaxonomic and genomic characterization was employed to ascertain the taxonomic position of the strains within the genus Flavobacterium. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity based on blast (ANIb) values for strains F-60^T and F-392 were calculated as 100 %. However, dDDH and ANI analyses between the strains and their close neighbours confirmed that both strains represent a novel species in the genus Flavobacterium. The strains shared the highest dDDH and ANIb levels of 23.3 and 77.9%, respectively, with the type strain of Flavobacterium frigidarium DSM 17623^T while those values for F. crassostreae LPB0076^T were obtained as 21.4-21.5 % and 76.3 %. The DNA G+C content of the strains was 34.5 mol%. Chemotaxonomic and phylogenomic analyses of these isolates confirmed that both strains are representatives of a novel species for which the name Flavobacterium muglaense sp. nov. is proposed, with F-60^T as the type strain (=JCM 34196^T=KCTC 82256^T).