Flavobacterium psychraquaticum sp. nov., isolated from water system of Atlantic salmon (Salmo salar) smolts cultured in Chile

Strain LB-N7T, a novel Gram-negative, orange, translucent, gliding, rod-shaped bacterium, was isolated from water samples collected from an open system of Atlantic salmon (Salmo salar) smolts in a fish farm in Chile during a flavobacterial infection outbreak in 2015. Phylogenetic analysis based on 16S rRNA sequences (1337 bp) revealed that strain LB-N7T belongs to the genus Flavobacterium and is closely related to the type strains Flavobacterium ardleyense A2-1T (98.8 %) and Flavobacterium cucumis R2A45-3T (96.75 %). The genome size of strain LB-N7T was 2.93 Mb with a DNA G+C content 32.6 mol%. Genome comparisons grouped strain LB-N7T with Flavobacterium cheniae NJ-26T, Flavobacterium odoriferum HXWNR29T, Flavobacterium lacisediminis TH16-21T and Flavobacterium celericrescens TWA-26T. The calculated digital DNA-DNA hybridization values between strain LB-N7T and the closest related Flavobacterium strains were 23.3 % and the average nucleotide identity values ranged from 71.52 to 79.39 %. Menaquinone MK-6 was the predominant respiratory quinone, followed by MK-7. The major fatty acids were iso-C15 : 0 and anteiso-C15 : 0. The primary polar lipids detected included nine unidentified lipids, two amounts of aminopospholipid and phospholipids, and a smaller amount of aminolipid. Phenotypic, genomic, and chemotaxonomic data suggest that strain LB-N7T (=CECT 30406T=RGM 3221T) represents as a novel bacterial species, for which the name Flavobacterium psychraquaticum sp. nov. is 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.

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.

Flavobacterium tagetis sp. nov., a novel urea-hydrolysing bacterium isolated from the roots of Tagetes patula

A Gram-stain-negative, rod-shaped, motile by gliding, non-sporulating and strictly aerobic bacterium, designated strain GN10^T, was isolated from the roots of Tagetes patula, collected from the garden of Dongguk University, Goyang, Republic of Korea. The cells could grow at 10-42 °C and at pH 5.5-9.0. Strain GN10^T was sensitive to NaCl and tolerated up to 4 % NaCl (w/v). Comparative analysis of 16S rRNA gene sequences revealed the highest similarities to Flavobacterium tistrianum GB 56.1^T (98.9 %), Flavobacterium sharifuzzamanii A7.6^T (98.6 %), Flavobacterium zhairuonense A5.7^T (98.3 %) and Flavobacterium anhuiense D3^T (98 %). Phylogenetic analysis showed that strain GN10^T clustered within the genus Flavobacterium and formed a monophyletic cluster with its close relative members. The average nucleotide identity and digital DNA-DNA hybridization values between strain GN10^T and related species belonging to the genus Flavobacterium were well below the standard threshold for prokaryotic species delineation. The DNA G+C content of strain GN10^T was 33.6 mol%. The predominant cellular fatty acids (>10 %) were identified as iso-C_15 : 0, C_16 : 0 and summed feature 3 (C_{16  : 1} ω6c and/or C_{16  :  1} ω7c). Strain GN10^T contained menaquinone 6 as the major respiratory quinone. The major polar lipids were phosphatidylethanolamine, three unidentified aminoglycolipids, two unidentified glycolipids, one unidentified phosphoglycolipid and five unidentified lipids. Urease is a nickel-containing enzyme found in archaea, bacteria, plants and unicellular eukaryotes. It serves as a virulence factor and is responsible for pathogenesis in humans and animals. Here, we describe a novel urease-hydrolysing bacterium, strain GN10^T. The urease activity of this strain may serve as an indicator of pathogenic potential and drug resistance, which may facilitate the development of many diseases. The results of physiological and biochemical tests allowed the genotypic and phenotypic differentiation of strain GN10^T from its closely related members and considered to represent novel species in the genus Flavobacterium, for which the name Flavobacterium tagetis (GN10^T=KCTC 82695^T=NBRC 114841^T) is proposed.

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

During a study on culturable microorganisms from fish farms, four yellow-pigmented gram negative, rod shaped isolates, F-47^T, F-339^T, F-380 and F-400, were recovered from rainbow trout samples exhibiting clinical signs. Based on 16S rRNA gene sequence analysis, the strains were identified as members of the genus Flavobacterium. Strains F-47^T and F-380 shared the highest 16S rRNA gene sequence identity level of 97.6% with the type strain of Flavobacterium frigoris DSM 15719^T while strains F-339^T and F-400 shared the highest identity level of 97.6% with the type strain of F. caseinilyticum AT-3-2^T. A polyphasic taxonomic approach including phenotypic and genomic characterization as well as whole-cell MALDI-TOF mass spectrometry analyses was employed to ascertain the taxonomic position of the strains within the genus Flavobacterium. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses between strains F-47^T, F-339^T and their close neighbours F. frigoris DSM 15719^T and F. caseinilyticum AT-3-2^T, respectively, confirmed that both strains represent novel species in the genus Flavobacterium. The DNA G+C contents of the strains F-47^T and F-339^T are 34.3% and 35.3%, respectively. It can be concluded on the basis of polyphasic characterization as well as pairwise genome comparisons that the strains F-47^T and F-339^T represent two novel species within the genus Flavobacterium, for which Flavobacterium kayseriense sp. nov. F-47^T (=JCM 34195^T=KCTC 82255^T) and Flavobacterium turcicum sp. nov. F-339^T (=JCM 34202^T=KCTC 82262^T) are proposed, respectively.