Complete genome sequence and potential pathogenic assessment of Flavobacterium plurextorum RSG-18 isolated from the gut of Schlegel's black rockfish, Sebastes schlegelii

Flavobacterium plurextorum is a potential fish pathogen of interest, previously isolated from diseased rainbow trout (Oncorhynchus mykiss) and oomycete-infected chum salmon (Oncorhynchus keta) eggs. We report here the first complete genome sequence of F. plurextorum RSG-18 isolated from the gut of Schlegel's black rockfish (Sebastes schlegelii). The genome of RSG-18 consists of a circular chromosome of 5,610,911 bp with a 33.57% GC content, containing 4858 protein-coding genes, 18 rRNAs, 63 tRNAs and 1 tmRNA. A comparative analysis was conducted on 11 Flavobacterium species previously reported as pathogens or isolated from diseased fish to confirm the potential pathogenicity of RSG-18. In the SEED classification, RSG-18 was found to have 36 genes categorized in 'Virulence, Disease and Defense'. Across all Flavobacterium species, a total of 16 antibiotic resistance genes and 61 putative virulence factors were identified. All species had at least one phage region and type I, III and IX secretion systems. In pan-genomic analysis, core genes consist of genes linked to phages, integrases and matrix-tolerated elements associated with pathology. The complete genome sequence of F. plurextorum RSG-18 will serve as a foundation for future research, enhancing our understanding of Flavobacterium pathogenicity in fish and contributing to the development of effective prevention strategies.

Draft genome sequence of the emerging fish pathogen Flavobacterium tructae strain S12

The draft genome of Flavobacterium tructae strain S12, isolated from hatchery-reared Chinook salmon (Oncorhynchus tshawytscha) fingerlings, consisted of 5,695,942 bp, a G + C content of 35.6%, 4,775 predicted open reading frames, a putative type IX secretion system, collagenase, and hemolysin. F. tructae strains can be used as models for emerging Flavobacterium pathogens.

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.

Identification of Flavobacterium algoritolerans sp. nov. and Flavobacterium yafengii sp. nov., two novel members of the genus Flavobacterium

Six psychrotolerant, Gram-stain-negative, aerobic bacterial strains, designated as LB1P51T, LB2P87T, LB2P84, LB3P48, LB3R18 and XS2P67, were isolated from glaciers on the Tibetan Plateau, PR China. The results of 16S rRNA gene analysis confirmed their classification within the genus Flavobacterium. Strain LB2P87T displayed the highest sequence similarity to Flavobacterium sinopsychrotolerans 0533T (98.18 %), while strain LB1P51T exhibited the highest sequence similarity to Flavobacterium glaciei CGMCC 1.5380T (98.15 %). Strains LB2P87T and LB1P51T had genome sizes of 3.8 and 3.9 Mb, respectively, with DNA G+C contents of 34.2 and 34.1 %, respectively. Pairwise average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) calculations revealed that these strains represented two distinct species within the genus Flavobacterium. The results of phylogenomic analysis using 606 core genes indicated that the six strains formed a distinct clade and were most closely related to F. glaciei CGMCC 1.5380T. The ANI and dDDH values between the two species and other members of the genus Flavobacterium were below 90.3 and 40.1 %, respectively. Genome relatedness, the results of phylogenomic analysis and phenotypic characteristics collectively support the proposal of two novel species of the genus Flavobacterium: Flavobacterium algoritolerans sp. nov. (LB1P51T = CGMCC 1.11237T = NBRC 114813T) and Flavobacterium yafengii sp. nov. (LB2P87T = CGMCC 1.11249T = NBRC 114814T).

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.

Secretion Systems in Gram-Negative Bacterial Fish Pathogens

Bacterial fish pathogens are one of the key challenges in the aquaculture industry, one of the fast-growing industries worldwide. These pathogens rely on arsenal of virulence factors such as toxins, adhesins, effectors and enzymes to promote colonization and infection. Translocation of virulence factors across the membrane to either the extracellular environment or directly into the host cells is performed by single or multiple dedicated secretion systems. These secretion systems are often key to the infection process. They can range from simple single-protein systems to complex injection needles made from dozens of subunits. Here, we review the different types of secretion systems in Gram-negative bacterial fish pathogens and describe their putative roles in pathogenicity. We find that the available information is fragmented and often descriptive, and hope that our overview will help researchers to more systematically learn from the similarities and differences between the virulence factors and secretion systems of the fish-pathogenic species described here.

The fish pathogen Flavobacterium columnare represents four distinct species: Flavobacterium columnare, Flavobacterium covae sp. nov., Flavobacterium davisii sp. nov. and Flavobacterium oreochromis sp. nov., and emended description of Flavobacterium columnare

Flavobacterium columnare is the causative agent of columnaris disease in freshwater fish and four discrete genetic groups exist within the species, suggesting that the species designation requires revision. The present study determined the taxonomic status of the four genetic groups of F. columnare using polyphasic and phylogenomic approaches and included five representative isolates from each genetic group (including type strain ATCC 23463^T; genetic group 1). 16S rRNA gene sequence analysis revealed genetic group 2 isolate AL-02-36^T, genetic group 3 isolate 90-106^T, and genetic group 4 isolate Costa Rica 04-02-TN^T shared less than <98.8 % sequence identity to F. columnare ATCC 23463^T. Phylogenetic analyses of 16S rRNA and gyrB genes using different methodologies demonstrated the four genetic groups formed well-supported and distinct clades within the genus Flavobacterium. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (GGDC) values between F. columnare ATCC 23463^T, genetic group 2 isolate AL-02-36^T, genetic group 3 isolate 90-106^T, and genetic group 4 isolate Costa Rica 04-02-TN^T were less than 90.84% and 42.7%, respectively. Biochemical and physiological characteristics were similar among the four genetic groups; however, quantitative differences in fatty acid profiles were detected and MALDI-TOF analyses demonstrated numerous distinguishing peaks unique to each genetic group. Chemotaxonomic, MALDI-TOF characterization and ANI/GGDC calculations afforded differentiation between the genetic groups, indicating each group is a discrete species. Herein, the names F. covae sp. nov. (AL-02-36^T), F. davisii sp. nov. (90-106^T), and F. oreochromis sp. nov. (Costa Rica 04-02-TN^T) are proposed to represent genetic groups 2, 3, and 4, respectively.

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.

Flavobacterium salmonis sp. nov. isolated from Atlantic salmon (Salmo salar) and formal proposal to reclassify Flavobacterium spartansii as a later heterotypic synonym of Flavobacterium tructae

A Gram-staining-negative non endospore-forming strain, T13(2019)T was isolated from water samples from Atlantic salmon (Salmo salar) fry culture in Chile and studied in detail for its taxonomic position. The isolate shared highest 16S rRNA gene sequence similarities with the type strains of Flavobacterium chungangense (98.44 %) followed by Flavobacterium tructae and Flavobacterium spartansii (both 98.22 %). Menaquinone MK-6 was the predominant respiratory quinone in T13(2019)T. Major polar lipids were phosphatidylethanolamine, an ornithine lipid and the unidentified polar lipids L1, L3 and L4 lacking a functional group. The major polyamine was sym-homospermidine. The fatty acid profile contained major amounts of iso-C15 : 0, iso-C15 : 0 3-OH, iso-C17 : 0 3-OH, C15 : 0, summed feature 3 (C16 : 1  ω7c and/or iso-C15 : 0 2-OH) and various hydroxylated fatty acids in smaller amounts, among them iso-C16 : 0 3-OH, and C15 : 0 3-OH, which supported the grouping of the isolate into the genus Flavobacterium . Physiological/biochemical characterisation and ANI calculations with the type strains of the most closely related species allowed a clear phenotypic and genotypic differentiation. In addition it became obvious, that the type strains of F. tructae and F. spartansii showed 100 % 16S rRNA gene sequence similarities and ANI values of 97.21%/ 97.59 % and DDH values of 80.40 % [77.5 and 83%]. These data indicate that F. tructae and F. spartansii belong to the same species and it is proposed that F. spartansii is a later heterotypic synonym of F. tructae . For strain T13(2019)T (=CIP 111411T=LMG 30298T=CCM 8798T) a new species with the name Flavobacterium salmonis sp. nov. is proposed.

Cross-protection of a live-attenuated Flavobacterium psychrophilum immersion vaccine against novel Flavobacterium spp. and Chryseobacterium spp. strains

For salmonid producers, a common threat is Flavobacterium psychrophilum. Recent advancements in bacterial coldwater disease (BCWD) management include the development of a live-attenuated immersion vaccine that cross-protects against an array of F. psychrophilum strains. Emerging family Flavobacteriaceae cases associated with clinical disease have been increasing, including pathogenic isolates of Flavobacterium spp. and Chryseobacterium spp. The cross-protective ability of a live-attenuated F. psychrophilum vaccine was determined against three virulent Flavobacteriaceae isolates. Juvenile rainbow trout were vaccinated, developed high F. psychrophilum-specific antibody titres and were challenged with Chryseobacterium spp. isolates (S25 and T28), a Flavobacterium sp. (S21) isolate, a mixed combination of S21:S25:T28, and a standard virulent F. psychrophilum CSF259-93 strain. Results demonstrated strong protection in the CSF259-93 vaccinated group (relative per cent survival (RPS)=94.44%) when compared to the relevant CSF259-93 controls (p < .001). Protection was also observed for vaccinated fish challenged with the S21:S25:T28 mix (RPS = 85.18%; p < .001). However, protection was not observed with the S21, S25 or T28 isolates alone. Analysis of whole-cell lysates revealed differences in protein banding by SDS-PAGE, but conserved antigenic regions by Western blot in S25 and T28. Results demonstrate that this live-attenuated vaccine provided protection against mixed flavobacterial infection and suggest further benefits against flavobacteriosis.

Genomic diversity in flavobacterial pathogens of aquatic origin

Flavobacterium species are considered important fish pathogens in wild and cultured fish throughout the world. They can cause acute, subacute, and chronic infections, which are mainly characterized by gill damage, skin lesions, and deep necrotic ulcerations. Primarily, three Flavobacterium species, F. branchiophilum, F. columnare, and F. psychrophilum, have been reported to cause substantial losses to freshwater fish. In this study, we evaluated genomes of 86 Flavobacterium species isolated from aquatic hosts (mainly fish) to identify their unique and shared genome features. Our results showed that F. columnare genomes cluster into four different genetic groups. In silico secretion system analysis identified that all genomes carry type I (T1SS) and type IX (T9SS) secretion systems, but the number of type I secretion system genes shows diversity between species. F. branchiophilum, F. araucananum, F. chilense, F. spartansii, and F. tructae genomes have full type VI secretion system (T6SS). F. columnare, F. hydatis, and F. plurextorum carry partial T6SS with some of the T6SS genes missing. F. columnare, F. araucananum, F. chilense, F. spartansii, F. araucananum, F. tructae, Flavobacterium sp., F. crassostreae, F. succinicans, F. hydatis, and F. plurextorum carry most of the type IV secretion system genes (T4SS). F. columnare genetic groups 1 and 2, Flavobacterium sp., and F. crassostreae encode the least number of antibiotic resistance elements. F. hydatis, F. chilense, and F. plurextorum encode the greatest number of antibiotic resistance genes. Additionally, F. spartansii, F. araucananum, and chilense encode the greatest number of virulence genes while Flavobacterium sp. and F. crassostreae encode the least number of virulence genes. In conclusion, comparative genomics of Flavobacterium species of aquatic origin will help our understanding of Flavobacterium pathogenesis.

Analysis of 1,000 Type-Strain Genomes Improves Taxonomic Classification of Bacteroidetes

Although considerable progress has been made in recent years regarding the classification of bacteria assigned to the phylum Bacteroidetes, there remains a need to further clarify taxonomic relationships within a diverse assemblage that includes organisms of clinical, piscicultural, and ecological importance. Bacteroidetes classification has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees and a limited number of phenotypic features. Here, draft genome sequences of a greatly enlarged collection of genomes of more than 1,000 Bacteroidetes and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa proposed long ago such as Bacteroides, Cytophaga, and Flavobacterium but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which can be considered valuable taxonomic markers. We detected many incongruities when comparing the results of the present study with existing classifications, which appear to be caused by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. The few significant incongruities found between 16S rRNA gene and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences and the impediment in using ordinary bootstrapping in phylogenomic studies, particularly when combined with too narrow gene selections. While a significant degree of phylogenetic conservation was detected in all phenotypic characters investigated, the overall fit to the tree varied considerably, which is one of the probable causes of misclassifications in the past, much like the use of plesiomorphic character states as diagnostic features.

Mobile Incubator for Iron(III) Reduction in the Gut of the Soil-Feeding Earthworm Pheretima guillelmi and Interaction with Denitrification

Diets of soil-feeding earthworms contain abundant nitrate and iron(III) oxides, which are potential electron acceptors for mineralization of organic compounds. The earthworm gut provides an ideal habitat for ingested iron(III)-reducing microorganisms. However, little is known about iron(III) reduction and its interaction with other processes in the guts of earthworms. Here, we determined the dynamics of iron(III) and revealed its interaction with the turnover of organic acids and nitrate in the gut of the earthworm Pheretima guillelmi. Samples from gut contents combined with anoxic incubation were used for chemical analysis and 16S rRNA based Illumina sequencing. Chemical analysis showed that higher ratios of iron(II)/iron(III), nitrite/nitrate, and more abundant organic acids were contained in the in vivo gut of the earthworm P. guillelmi than those in the in situ soil. A higher rate of iron(III) reduction was detected in treatments of microcosmic incubation with gut contents (IG gut) than that with soil (IG soil), and nitrate reduction occurred earlier than iron(III) reduction in both treatments. Potential iron(III) reducers were dominated by fermentative genera Clostridium, Bacillus, and Desulfotomaculum in the treatment of IG gut, while they were dominated by dissimilatory iron(III)-reducing genera Geobacter in the treatment of IG soil. The iron(III)-reducing microbial community shared several genera with denitrifers in the treatment of IG gut, revealing a close link between iron(III) reduction and denitrification in the gut of earthworms. Collectively, our findings demonstrated that iron(III) reduction occurred along the gut and provided novel insights into the great contribution of earthworm gut microbiota on Fe and the associated C and N cycling in soil environments.

Flavobacterium ureilyticum sp. nov., a novel urea hydrolysing bacterium isolated from stream bank soil

A novel bacterium designated S-42^T was isolated from stream bank soil. Cells were found to be aerobic, Gram staining-negative, oxidase-positive, catalase-negative, non-motile, non-spore-forming, rod-shaped, and yellow-pigmented. The strain can grow at 15-35 °C, pH 6.0-10.0, and at 0.5% (w/v) NaCl concentration. Urea was hydrolysed. Flexirubin-type pigments were absent. Phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain S-42^T formed a lineage within the family Flavobacteriaceae of the phylum Bacteroidetes that is distinct from various species of the genus Flavobacterium, including Flavobacterium maotaiense T9^T (97.6% sequence similarity), Flavobacterium hibernum ATCC 51468^T (97.4%), and Flavobacterium granuli Kw05^T (97.1%). The 16S rRNA gene sequences identity between strain S-42^T and other members of the genus Flavobacterium were < 97.0%. Strain S-42^T contains MK-6 as sole respiratory quinone. The major polar lipids were identified as phosphatidylethanolamine and an unidentified aminolipid. The major cellular fatty acids were identified as iso-C_15:0, summed feature 3 (C_16:1ω7c and/or C_{16: 1}ω6c), C_16:0, anteiso-C_15:0, iso-C_17:0 3-OH, iso-C_15:0 3-OH, and iso-C_15:1 G. The DNA G + C content of the strain was 35.8 mol%. The polyphasic characterization indicated that strain S-42^T represents a novel species of the genus Flavobacterium, for which the name Flavobacterium ureilyticum sp. nov. is proposed. The type strain is S-42^T (= KEMB 9005-537^T = KACC 19115^T = NBRC 112683^T).

Holobionts and ecological speciation: the intestinal microbiota of lake whitefish species pairs

BACKGROUND

It is well established that symbionts have considerable impact on their host, yet the investigation of the possible role of the holobiont in the host's speciation process is still in its infancy. In this study, we compared the intestinal microbiota among five sympatric pairs of dwarf (limnetic) and normal (benthic) lake whitefish Coregonus clupeaformis representing a continuum in the early stage of ecological speciation. We sequenced the 16s rRNA gene V3-V4 regions of the intestinal microbiota present in a total of 108 wild sympatric dwarf and normal whitefish as well as the water bacterial community from five lakes to (i) test for differences between the whitefish intestinal microbiota and the water bacterial community and (ii) test for parallelism in the intestinal microbiota of dwarf and normal whitefish.

RESULTS

The water bacterial community was distinct from the intestinal microbiota, indicating that intestinal microbiota did not reflect the environment, but rather the intrinsic properties of the host microbiota. Our results revealed a strong influence of the host (dwarf or normal) on the intestinal microbiota with pronounced conservation of the core intestinal microbiota (mean ~ 44% of shared genera). However, no clear evidence for parallelism was observed, whereby non-parallel differences between dwarf and normal whitefish were observed in three of the lakes while similar taxonomic composition was observed for the two other species pairs.

CONCLUSIONS

This absence of parallelism across dwarf vs. normal whitefish microbiota highlighted the complexity of the holobiont and suggests that the direction of selection could be different between the host and its microbiota.

The Emerging Fish Pathogen Flavobacterium spartansii Isolated from Chinook Salmon: Comparative Genome Analysis and Molecular Manipulation

Flavobacterium spartansii strain T16^T was isolated from a disease outbreak in hatchery-reared Chinook salmon (Oncorhynchus tshawytscha) fingerlings. To gain insight into its genomic content, structure and virulence pathogenesis factors, comparative genome analyses were performed using genomes from environmental and virulent Flavobacterium strains. F. spartansii shared low average nucleotide identity (ANI) to well-known fish-pathogenic flavobacteria (e.g., F. columnare, F. psychrophilum, and F. branchiophilum), indicating that it is a new and emerging fish pathogen. The genome in T16^T had a length of 5,359,952 bp, a GC-content 35.7%, and 4,422 predicted protein-coding sequences. Flavobacterium core genome analysis showed that the number of shared genes decreased with the addition of input genomes and converged at 1182 genes. At least 8 genomic islands and 5 prophages were predicted in T16^T. At least 133 virulence factors associated with virulence in pathogenic bacteria were highly conserved in F. spartansii T16^T. Furthermore, genes linked to virulence in other bacterial species (e.g., those encoding for a type IX secretion system, collagenase and hemolysin) were found in the genome of F. spartansii T16^T and were conserved in most of the analyzed pathogenic Flavobacterium. F. spartansii was resistant to ampicillin and penicillin, consistent with the presence of multiple genes encoding diverse lactamases and the penicillin-binding protein in the genome. To allow for future investigations into F. spartansii virulence in vivo, a transposon-based random mutagenesis strategy was attempted in F. spartansii T16^T using pHimarEm1. Four putative gliding motility deficient mutants were obtained and the insertion sites of pHimarEm1 in the genome of these mutants were characterized. In total, study results clarify some of the mechanisms by which emerging flavobacterial fish pathogens may cause disease and also provide direly needed tools to investigate their pathogenesis.

Revised phylogeny of Bacteroidetes and proposal of sixteen new taxa and two new combinations including Rhodothermaeota phyl. nov

Members of the phylum Bacteroidetes, which was originally defined as a monophyletic branch encompassing the genera Cytophaga, Flavobacterium and Bacteroides (CFB), are widely studied due to their importance in environmental and gut microbiology. As a consequence, the number of species names with standing in nomenclature has doubled in the past five years. In this study, a revision of an earlier phylogeny of Bacteroidetes has been performed using the 16S rRNA gene as a backbone in combination with the 23S rRNA gene, as well as multilocus sequence analysis (MLSA) of 29 orthologous protein sequences, and indels in the sequences of the beta subunit of the F-type ATPase and the alanyl-tRNA synthetase. In addition, taxonomic data for Bacteroidetes has been updated by considering the orphan species list, signature nucleotides in the 16S rRNA sequence, the list of outlier species, and discrepancies with the current taxonomy at the genus rank level. As a result, seven new taxa are proposed within Bacteroidetes (Chitinophagia classis nov., Chitinophagales ord. nov., Crocinitomicaceae fam. nov., Odoribacteraceae fam. nov., Hymenobacteraceae fam. nov., Thermonemataceae fam. nov. and Persicobacteraceae fam. nov.), as well as one new phylum Rhodothermaeota phyl. nov. that contains two classes, two orders, four families and a new genus with two new combinations.

Antibacterial activity of aquatic gliding bacteria

The study aimed to screen and isolate strains of freshwater aquatic gliding bacteria, and to investigate their antibacterial activity against seven common pathogenic bacteria. Submerged specimens were collected and isolated for aquatic gliding bacteria using four different isolation media (DW, MA, SAP2, and Vy/2). Gliding bacteria identification was performed by 16S rRNA gene sequencing and phylogenetic analysis. Crude extracts were obtained by methanol extraction. Antibacterial activity against seven pathogenic bacteria was examined by agar-well diffusion assay. Five strains of aquatic gliding bacteria including RPD001, RPD008, RPD018, RPD027 and RPD049 were isolated. Each submerged biofilm and plastic specimen provided two isolates of gliding bacteria, whereas plant debris gave only one isolate. Two strains of gliding bacteria were obtained from each DW and Vy/2 isolation medium, while one strain was obtained from the SAP2 medium. Gliding bacteria strains RPD001, RPD008 and RPD018 were identified as Flavobacterium anhuiense with 96, 82 and 96 % similarity, respectively. Strains RPD049 and RPD027 were identified as F. johnsoniae and Lysobacter brunescens, respectively, with similarity equal to 96 %. Only crude extract obtained from RPD001 inhibited growth of Listeria monocytogenes (MIC 150 µg/ml), Staphylococcus aureus (MIC 75 µg/ml) and Vibrio cholerae (MIC 300 µg/ml), but showed weak inhibitory effect on Salmonella typhimurium (MIC > 300 µg/ml). Gliding bacterium strain RPD008 should be considered to a novel genus separate from Flavobacterium due to its low similarity value. Crude extract produced by RPD001 showed potential for development as a broad antibiotic agent.

Flavobacterium endophyticum sp. nov., a nifH gene-harbouring endophytic bacterium isolated from maize root

A novel Gram-stain-negative, aerobic, rod-shaped bacterium, designated strain 522T, was isolated from surface-sterilized root tissue of maize planted in Fangshan District of Beijing, China. A polyphasic taxonomic study was performed on the new isolate. On the basis of 16S rRNA gene sequence similarity studies, this isolate belonged to the genus Flavobacterium and showed less than 93.9 % similarity to the type strains of all recognized species of the genus Flavobacterium. The predominant respiratory quinone was menaquinone-6 and the polar lipid profile was composed of the major lipids phosphatidylethanolamine, phosphatidylserine and two unidentified amino lipids. The major fatty acids were C15 : 0, iso-C15 : 0, iso-C15 : 1 G and iso-C16 : 0.The G+C content of the DNA was 37.7 mol%. The results of physiological and biochemical tests and the differences in fatty acid profiles allowed the clear phenotypic differentiation of strain 522T from closely related species of the genus Flavobacterium. Strain 522T therefore represents a novel species within the genus Flavobacterium, for which the name Flavobacterium endophyticum sp. nov. is proposed. The type strain is 522T ( = ACCC 19708T = DSM 29537T).

Flavobacterium notoginsengisoli sp. nov., isolated from the rhizosphere of Panax notoginseng

Two novel bacterial strains, designated SYP-B540(T) and SYP-B556, were isolated from rhizospheric soil of Panax notoginseng located at Yunnan Province, China. Both strains were Gram-staining negative, aerobic, non-motile, elongated rod shaped and yellow coloured. They grew optimally at 28 °C and pH 7.0. Analysis of 16S rRNA gene sequences showed that the two strains shared 99.8 % sequence similarity to each other, but lower than 97.6 % to the other known species of the genus Flavobacterium. The predominant respiratory quinone for the two strains was MK-6, and the major fatty acids were iso-C15:0 and summed Feature 3 (comprising 16:1 ω7c and/or 16:1 ω6c). The polar lipids consisted of phosphatidylethanolamine, two unidentified polar lipids and three unidentified amino-phospholipids. The DNA G+C contents of strains SYP-B540(T) and SYP-B556 were 33.3 and 32.7 mol%, respectively. In addition, the DNA-DNA hybridization values of strains SYP-B540(T) and SYP-B556 to their closest phylogenetic neighbors were significantly lower than 70 %. On the basis of the polyphasic taxonomy studies, strains SYP-B540(T) and SYP-B556 represent a novel species of the genus Flavobacterium, for which the name Flavobacterium notoginsengisoli sp. nov. is proposed. The type strain is SYP-B540(T) (=KCTC 32505(T) = NBRC 110012(T) = BCRC 80724(T)).

Flavobacterium gyeonganense sp. nov., isolated from freshwater, and emended descriptions of Flavobacterium chungangense, Flavobacterium aquidurense, Flavobacterium tructae and Flavobacterium granuli

A Gram-stain-negative, aerobic and rod-shaped bacterial strain, designated HME7524T, was isolated from freshwater of Gyeong-an stream in Korea. A phylogenetic tree based on 16S rRNA gene sequences showed that strain HME7524T formed a distinct lineage within the genus Flavobacterium and exhibited high sequence similarity with Flavobacterium chungangense CJ7T (96.9 %), Flavobacterium aquidurense WB-1.1.56T (96.9 %), Flavobacterium tructae 435-08T (96.9 %) and Flavobacterium granuli Kw05T (96.9 %). The major fatty acids of strain HME7524T were iso-C15 : 0 (26.5 %) and summed feature 3 (comprising C16 : 1ω6c and/or C16 : 1ω7c; 17.4 %). The major polar lipids were phosphatidylethanolamine, two unidentified aminolipids and three unidentified polar lipids. The major respiratory quinone was MK-6. The DNA G+C content of strain HME7524T was 34.2 mol%. On the basis of the evidence presented in this study, strain HME7524T represents a novel species of the genus Flavobacterium , for which the name Flavobacterium gyeonganense sp. nov., is proposed. The type strain is HME7524T ( = KACC 17688T = CECT 8365T). Emended descriptions of Flavobacterium chungangense , Flavobacterium aquidurense , Flavobacterium tructae and Flavobacterium granuli are also provided.

Deciphering the biodiversity of fish-pathogenic Flavobacterium spp. recovered from the Great Lakes basin

Flavobacterial diseases negatively impact wild and cultured fishes worldwide. We recently reported on the presence of a large and diverse group of flavobacteria, many of which were associated with lesions in a number of Great Lakes fish species. Herein, we report on the characterization of 65 fish-associated Flavobacterium spp. isolates using 16S rRNA gene sequence analysis and phylogenetic analyses based upon neighbor-joining and Bayesian methodologies. Thirteen isolates were identified as the newly described fish-associated F. plurextorum, F. spartansii, and F. tructae, while 3 isolates were similar to F. frigidimaris; however, the remaining Flavobacterium spp. isolates did not conclusively match any described Flavobacterium spp. and thus were suspected as comprising novel flavobacterial species. A more comprehensive polyphasic characterization was undertaken on 6 isolates, representing a range of association with disease signs in hatchery-raised or free-ranging fish and genetic distinctness. Polyphasic characterization included physiological, morphological, and biochemical analyses, as well as additional phylogenetic analyses based upon near-complete sequencing of the 16S rRNA gene. Our findings demonstrated that that at least 5 of the 6 isolates are most likely novel species within the genus Flavobacterium that have never before been reported from fish. Pilot experimental challenge studies suggested that some of these Flavobacterium spp. can cause pathological lesions in fish and were re-isolated from the brains, spleens, livers, and kidneys of experimentally infected fish. The findings underscore the growing number and heterogeneity of flavobacteria now known to be capable of infecting fish.

Emerging flavobacterial infections in fish: A review

Flavobacterial diseases in fish are caused by multiple bacterial species within the family Flavobacteriaceae and are responsible for devastating losses in wild and farmed fish stocks around the world. In addition to directly imposing negative economic and ecological effects, flavobacterial disease outbreaks are also notoriously difficult to prevent and control despite nearly 100 years of scientific research. The emergence of recent reports linking previously uncharacterized flavobacteria to systemic infections and mortality events in fish stocks of Europe, South America, Asia, Africa, and North America is also of major concern and has highlighted some of the difficulties surrounding the diagnosis and chemotherapeutic treatment of flavobacterial fish diseases. Herein, we provide a review of the literature that focuses on Flavobacterium and Chryseobacterium spp. and emphasizes those associated with fish.

Chryseobacterium aahli sp. nov., isolated from lake trout (Salvelinus namaycush) and brown trout (Salmo trutta), and emended descriptions of Chryseobacterium ginsenosidimutans and Chryseobacterium gregarium

Two strains (T68T and T62) of a Gram-reaction-negative, yellow-pigmented bacterium containing flexirubin-type pigments were recovered from the kidney of a cultured lake trout (Salvelinus namaycush) and necrotic fins of a brown trout (Salmo trutta) during disease surveillance in 2009. Both isolates possessed catalase and cytochrome oxidase activities and degraded multiple substrates (e.g. gelatin, casein, elastin and Tweens 20 and 80). The mean DNA G+C content of strain T68T was 34.1 mol%. 16S rRNA gene sequencing demonstrated that strains T68T and T62 had nearly identical sequences (≥99 % similarity) and placed the bacterium within the genus Chryseobacterium , where Chryseobacterium ginsenosidimutans THG 15T (97.8 %), C. gregarium DSM 19109T (97.7 %) and C. soldanellicola PSD1-4T (97.6 %) were its closest relatives. Subsequent phylogenetic analyses using neighbour-joining, maximum-parsimony and Bayesian methodologies demonstrated that strains T68T and T62 formed a well-supported clade (bootstrap values of 100 and 97 %; posterior probability 0.99) that was distinct from other species of the genus Chryseobacterium . The major fatty acids of strains T68T and T62 were characteristic of the genus Chryseobacterium and included iso-C15 : 0, summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), iso-C17 : 0 3-OH, C16 : 0 and C16 : 0 3-OH. The mean DNA–DNA relatedness of strain T68T to C. ginsenosidimutans JCM 16719T and C. gregarium LMG 24952T was 24 and 21 %, respectively. Based on the results from our polyphasic characterization, strains T68T and T62 represent a novel species of the genus Chryseobacterium , for which the name Chryseobacterium aahli sp. nov. is proposed. The type strain is T68T ( = LMG 27338T = ATCC BAA-2540T). Emended descriptions of Chryseobacterium ginsenosidimutans and Chryseobacterium gregarium are also proposed.