Advancements in Characterizing Tenacibaculum Infections in Canada

The use of salmonid epithelial cells to characterize the toxicity of Tenacibaculum maritimum soluble extracellular products

AIMS

This study assessed how the etiological agent of mouth rot in farmed Atlantic salmon, Tenacibaculum maritimum, induces toxicity in host salmonid barrier cells, and determined whether environmental changes are relevant for these effects.

METHODS AND RESULTS

Tenacibaculum maritimum soluble extracellular products (ECPs) were collected and used to treat Atlantic salmon and rainbow trout intestinal barrier cell lines as a comparative model of bacterial-salmonid cell interactions. Cellular assays that examine cell membrane integrity, marker expression, and metabolic activity revealed that T. maritimum ECPs induced salmonid epithelial cell death through an apoptosis mechanism. Changes in salinity (25, 29, and 33 ppt) and temperature (12°C, 18°C, and 24°C) within the natural ranges observed in Pacific Northwest aquaculture facilities affected bacterial growth and cytotoxicity of T. maritimum ECPs.

CONCLUSIONS

Our results suggest epithelial barriers as targets of T. maritimum-mediated toxicity in farmed mouth rot-infected Atlantic salmon. The induction of apoptosis by T. maritimum soluble ECPs may also help to explain the absence of overt inflammation typically reported for these fish.

Genetic and phenotypical diversity of Pseudomonas syringae population in the Russian Federation

Abstract Proteobacteria comprising species of Pseudomonas syringae group cause diseases of many plants around the world. The phytopathogen has a complex taxonomic structure, which is constantly being revised due to the emergence of new molecular and biochemical diagnostic methods. Here for the first time, we describe the genetic and phenotypic diversity of 57 strains of Pseudomonas syringae isolated from affected soybeans, cereals, sunflowers, and other plants in the Russian Federation from 1950 to 2019. Genetic diversity was assessed by Multi Locus Sequence Analysis (MLSA) using fragments of the genes of glyceraldehyde-3-phosphate dehydrogenase (gapdh), the DNA-directed RNA polymerase subunit D (rpoD), gyrase (topoisomerase) B subunit (gyrB), and citrate synthase I (gltA). The synthesis of syringomycin and coronatine by bacteria was assessed by the reaction of susceptible yeast culture, seedlings of barley, tomato, and sunflower, and by presence of toxin genes confirmed by PCR test. The pathogenicity of the strains was confirmed on seedlings of dicotyledonous and monocotyledonous plants of peas, soybean, sunflowers, barley and wheat, as the most affected crops. The sensitivity of bacteria to 10 antibiotics of the main mechanisms of activity and two bactericidal commercial products was tested by standard disc method. The obtained results showed a high genetic homogeneity of the Russian population of P. syringae, which infects various agricultural crops, and an increase in the proportion of antibiotic-resistant strains over the years.

Holobiont responses of mesophotic precious red coral Corallium rubrum to thermal anomalies

Marine heat waves (MHWs) have increased in frequency and intensity worldwide, causing mass mortality of benthic organisms and loss of biodiversity in shallow waters. The Mediterranean Sea is no exception, with shallow populations of habitat-forming octocorals facing the threat of local extinction. The mesophotic zone, which is less affected by MHWs, may be of ecological importance in conservation strategies for these species. However, our understanding of the response of mesophotic octocoral holobionts to changes in seawater temperature remains limited. To address this knowledge gap, we conducted a study on an iconic Mediterranean octocoral, the red coral Corallium rubrum sampled at 60 m depth and 15 °C. We exposed the colonies to temperatures they occasionally experience (18 °C) and temperatures that could occur at the end of the century if global warming continues (21 °C). We also tested their response to extremely cold and warm temperatures (12 °C and 24 °C). Our results show a high tolerance of C. rubrum to a two-month long exposure to temperatures ranging from 12 to 21 °C as no colony showed signs of tissue loss, reduced feeding ability, stress-induced gene expression, or disruption of host-bacterial symbioses. At 24 °C, however, we measured a sharp decrease in the relative abundance of Spirochaetaceae, which are the predominant bacterial symbionts under healthy conditions, along with a relative increase in Vibrionaceae. Tissue loss and overexpression of the tumor necrosis factor receptor 1 gene were also observed after two weeks of exposure. In light of ongoing global warming, our study helps predict the consequences of MHWs on mesophotic coralligenous reefs and the biodiversity that depends on them.

Comparative genomic assessment of members of genus Tenacibaculum: an exploratory study

Tenacibaculosis is an ulcerative skin disorder that affects finfish. It is caused by members of the genus Tenacibaculum, resulting in eccentric behavioural changes, including anorexia, lethargy, and abnormal swimming patterns that often result in mortality. Currently, species suspected of causing fish mortality include T. ovolyticum, T. gallaicum, T. discolor, T. finnmarkense, T. mesophilum, T. soleae, T. dicentrarchi, and T. maritimum. However, pathogenic members and the mechanisms involved in disease causation, progression, and transmission are limited due to the inadequate sequencing efforts in the past decade. In this study, we use a comparative genomics approach to investigate the characteristic features of 26 publicly available genomes of Tenacibaculum and report our observations. We propose the reclassification of "T. litoreum HSC 22" to the singaporense species and assignment of "T. sp. 4G03" to the species discolor (species with quotation marks have not been appropriately named). We also report the co-occurrence of several antimicrobial resistance/virulence genes and genes private to a few members. Finally, we mine several non-B DNA forming regions, operons, tandem repeats, high-confidence putative effector proteins, and sortase that might play a pivotal role in bacterial evolution, transcription, and pathogenesis.

Infectious agents and their physiological correlates in early marine Chinook salmon (Oncorhynchus tshawytscha)

The early marine life of Pacific salmon is believed to be a critical period limiting population-level survival. Recent evidence suggests that some infectious agents are associated with survival but linkages with underlying physiological mechanisms are lacking. While challenge studies can demonstrate cause and effect relationships between infection and pathological change or mortality, in some cases pathological change may only manifest in the presence of environmental stressors; thus, it is important to gain context from field observations. Herein, we examined physiological correlates with infectious agent loads in Chinook salmon during their first ocean year. We measured physiology at the molecular (gene expression), metabolic (plasma chemistry) and cellular (histopathology) levels. Of 46 assayed infectious agents, 27 were detected, including viruses, bacteria and parasites. This exploratory study identified.

a strong molecular response to viral disease and pathological change consistent with jaundice/anemia associated with Piscine orthoreovirus,strong molecular signals of gill inflammation and immune response associated with gill agents `Candidatus Branchiomonas cysticola' and Parvicapsula pseudobranchicola,a general downregulation of gill immune response associated with Parvicapsula minibicornis complementary to that of P. pseudobranchicola.Importantly, our study provides the first evidence that the molecular activation of viral disease response and the lesions observed during the development of the PRV-related disease jaundice/anemia in farmed Chinook salmon are also observed in wild juvenile Chinook salmon.

Shell disease syndromes of decapod crustaceans

The term shell disease subsumes a number of debilitating conditions affecting the outer integument (the carapace) of decapod crustaceans, such as lobsters and crabs. Herein, we seek to find commonality in the aetiology and pathology of such conditions, and those cases that result in the progressive erosion of the cuticle through to the visceral tissues by a cocktail of microbial-derived enzymes including lipases, proteases and chitinases. Aquimarina spp. are involved in shell disease in many different crustaceans across a wide geographical area, but the overall view is that the condition is polymicrobial in nature leading to dysbiosis within the microbial consortium of the damaged cuticle. The role of environment, decapod behaviour and physiology in triggering this disease is also reviewed. Finally, we provide a conceptual model for disease aetiology and suggest several avenues for future research that could improve our understanding of how such factors trigger, or exacerbate, this condition.

Genomics of Tenacibaculum Species in British Columbia, Canada

Tenacibaculum is a genus of Gram-negative filamentous bacteria with a cosmopolitan distribution. The research describing Tenacibaculum genomes stems primarily from Norway and Chile due to their impacts on salmon aquaculture. Canadian salmon aquaculture also experiences mortality events related to the presence of Tenacibaculum spp., yet no Canadian Tenacibaculum genomes are publicly available. Ribosomal DNA sequencing of 16S and four species-specific 16S quantitative-PCR assays were used to select isolates cultured from Atlantic salmon with mouthrot in British Columbia (BC), Canada. Ten isolates representing four known and two unknown species of Tenacibaculum were selected for shotgun whole genome sequencing using the Oxford Nanopore's MinION platform. The genome assemblies achieved closed circular chromosomes for seven isolates and long contigs for the remaining three isolates. Average nucleotide identity analysis identified T. ovolyticum, T. maritimum, T. dicentrarchi, two genomovars of T. finnmarkense, and two proposed novel species T. pacificus sp. nov. type strain 18-2881-A^T and T. retecalamus sp. nov. type strain 18-3228-7B^T. Annotation in most of the isolates predicted putative virulence and antimicrobial resistance genes, most-notably toxins (i.e., hemolysins), type-IX secretion systems, and oxytetracycline resistance. Comparative analysis with the T. maritimum type-strain predicted additional toxins and numerous C-terminal secretion proteins, including an M12B family metalloprotease in the T. maritimum isolates from BC. The genomic prediction of virulence-associated genes provides important targets for studies of mouthrot disease, and the annotation of the antimicrobial resistance genes provides targets for surveillance and diagnosis in veterinary medicine.

Tenacibaculosis caused by Tenacibaculum maritimum: Updated knowledge of this marine bacterial fish pathogen

Tenacibaculosis occurs due to the marine bacterial pathogen Tenacibaculum maritimum. This ulcerative disease causes high mortalities for various marine fish species worldwide. Several external clinical signs can arise, including mouth erosion, epidermal ulcers, fin necrosis, and tail rot. Research in the last 15 years has advanced knowledge on the traits and pathogenesis mechanisms of T. maritimum. Consequently, significant progress has been made in defining the complex host-pathogen relationship. Nevertheless, tenacibaculosis pathogenesis is not yet fully understood. Continued research is urgently needed, as demonstrated by recent reports on the re-emerging nature of tenacibaculosis in salmon farms globally. Current sanitary conditions compromise the development of effective alternatives to antibiotics, in addition to hindering potential preventive measures against tenacibaculosis. The present review compiles knowledge of T. maritimum reported after the 2006 review by Avendaño-Herrera and colleagues. Essential aspects are emphasized, including antigenic and genomic characterizations and molecular diagnostic procedures. Further summarized are the epidemiological foundations of the T. maritimum population structure and elucidations as to the virulence mechanisms of pathogenic isolates, as found using biological, microbiological, and genomic techniques. This comprehensive source of reference will undoubtable serve in tenacibaculosis prevention and control within the marine fish farming industry. Lastly, knowledge gaps and valuable research areas are indicated as potential guidance for future studies.

Isolation and characterization of a novel Tenacibaculum species and a corresponding bacteriophage from a Mediterranean fish hatchery: Description of Tenacibaculum larymnensis sp. nov. and Tenacibaculum phage Larrie

Tenacibaculum larymnensis sp. nov., a novel species of the Tenacibaculum genus was isolated from a commercial fish hatchery in Greece. The novel species is phylogenetically close to T. discolor and was biochemically and genetically characterized. The genome of T. larymnensis has 3.66 Mbps length, 31.83% GC content and the genomic analysis demonstrated that it harbors a wide enzymatic repertoire suggestive of increased degrading capacity but also several virulence factors including hemolysins, secretion systems, transporters, siderophores, pili and extracellular proteins. Using the novel strain, a virulent bacteriophage designated as Tenacibaculum phage Larrie was isolated and characterized. Larrie is a novel Siphovirus with relatively large genome, 77.5 kbps with 111 ORFs, a GC content of 33.7% and an exclusively lytic lifestyle. The new phage-host system can serve as an efficient model to study microbial interactions in the aquatic environment which contribute to the nutrient cycling.

Opportunistic diseases in marine eukaryotes: Could Bacteroidota be the next threat to ocean life?

Bacteria within the phylum Bacteroidota (Bacteroidetes) are known to cause devastating and widespread disease outbreaks in marine eukaryotic hosts. However, with few pathogens described in detail, their prevalence and virulence strategies remain largely unknown. Here, we systematically reviewed the literature to evaluate the current understanding of Bacteroidota that cause disease in marine hosts. Isolates affiliated with the genera Tenacibaculum and Aquimarina (Flavobacteriaceae) were the most widely reported and characterized pathogens. Although cultured isolates were predominantly Flavobacteriia, culture-independent studies also found classes Bacteroidia, Cytophagia and Sphingobacteriia associated with disease. We found that pathogenic marine Bacteroidota largely conformed to an opportunistic lifestyle but could also act as secondary pathogens or were involved in polymicrobial diseases. Many diseases were also associated with an environmental stressor, especially those affecting coral, macroalgae and fish. Key virulence traits included the production of adhesins and host tissue-degrading enzymes. Overall, the nature of disease involving Bacteroidota pathogens appears to be an outcome of complex host-pathogen-environment interactions; however, our understanding of virulence remains limited by the lack of functional characterization studies. This is concerning as Bacteroidota have the potential to emerge as a serious threat to marine ecosystems and aquaculture industries, driven by global changes in ocean conditions.

Bacteriology & bivalves: Assessing diagnostic tools for geographically remote bivalve populations

Two sampling approaches for the growth of common or dominant bacteria from bivalve haemolymph were compared: (1) samples processed in the field immediately after collection (field samples), and (2) samples processed in the laboratory at least 24 h after collection (laboratory samples). The sampling approaches were compared on 210 marine bivalve molluscs Paphies subtriangulata and P. australis from two shallow intertidal sites in North Island New Zealand. The approaches were evaluated for the amount of bacterial growth, type of growth, and diversity of growth. Differences in amount and type of growth between the two sampling approaches were observed. Samples processed in the field from P. subtriangulata had significantly more bacterial growth, and a higher diversity of bacteria, including more common or dominant bacterial species. Laboratory samples had a higher proportion of samples with no growth, however common or dominant bacteria were still isolated from these samples. For P. australis, field samples more often had no bacterial growth and laboratory samples had a significantly higher number of common or dominant growth present. Field samples did however contain a higher diversity of bacteria. By conducting bacteriology on bivalves in either the field or the laboratory only, there may be limitations to determining the significance of a bacterial agent isolated. Sampling of both field and laboratory samples should be carried out where possible to optimise detection of important bacteria.

Genomic characterization of Tenacibaculum maritimum O-antigen gene cluster and development of a multiplex PCR-based serotyping scheme

Tenacibaculum maritimum is a devastating bacterial pathogen affecting a large variety of marine fish species. It is responsible for significant economic losses in aquaculture farms worldwide. Different typing methods have been proposed to analyse bacterial diversity and population structure. Serological heterogeneity has been observed and up to four different serotypes have been described so far. However, the underlying molecular factors remain unknown. By combining conventional serotyping and genome-wide association study, we identified the genomic loci likely involved in the O-antigen biosynthesis. This finding allowed the development of a robust multiplex PCR-based serotyping scheme able to detect subgroups within each serotype and therefore performs better than conventional serotyping. This scheme was successfully applied to a large number of isolates from worldwide origin and retrieved from a large variety of fish species. No obvious correlations were observed between the mPCR-based serotype and the host species or the geographic origin of the isolates. Strikingly, the distribution of mPCR-based serotypes does not follow the core genome phylogeny. Nevertheless, this simple and cost-effective mPCR-based serotyping method could be useful for different applications such as population structure analysis, disease surveillance, vaccine formulation and efficacy follow-up.

Surface microbiota of Mediterranean loggerhead sea turtles unraveled by 16S and 18S amplicon sequencing

The loggerhead sea turtle is considered a keystone species with a major ecological role in Mediterranean marine environment. As is the case with other wild reptiles, their outer microbiome is rarely studied. Although there are several studies on sea turtle’s macro-epibionts and endo-microbiota, there has been little research on epibiotic microbiota associated with turtle skin and carapace. Therefore we aimed to provide the identification of combined epibiotic eukaryotic, bacterial and archaeal microbiota on Mediterranean loggerhead sea turtles. In this study, we sampled skins and carapaces of 26 loggerheads from the Mediterranean Sea during 2018 and 2019. To investigate the overall microbial diversity and composition, amplicon sequencing of 16S and 18S rRNA genes was performed. We found that the Mediterranean loggerhead sea turtle epibiotic microbiota is a reservoir of a vast variety of microbial species. Microbial communities mostly varied by different locations and seas, while within bacterial communities’ significant difference was observed between sampled body sites (carapace vs. skin). In terms of relative abundance, Proteobacteria and Bacteroidota were the most represented phyla within prokaryotes, while Alveolata and Stramenopiles thrived among eukaryotes. This study, besides providing a first survey of microbial eukaryotes on loggerheads via metabarcoding, identifies fine differences within both bacterial and eukaryotic microbial communities that seem to reflect the host anatomy and habitat. Multi-domain epi-microbiome surveys provide additional layers of information that are complementary with previous morphological studies and enable better understanding of the biology and ecology of these vulnerable marine reptiles.

Draft Genome Sequence of Tenacibaculum ovolyticum To-7Br, Recovered from a Farmed Atlantic Salmon (Salmo salar)

We present the draft genome sequence of Tenacibaculum ovolyticum isolate To-7Br, recovered from a gill of a farmed specimen of Atlantic salmon (Salmo salar) showing signs of tenacibaculosis. This study provides the first detailed insights into the genomic characteristics of T. ovolyticum isolated for the first time from fish farmed in Chile.

Low Dose of Sucralose Alter Gut Microbiome in Mice

Sucralose is a non-nutritive artificial sweetener (NNS) used in foods or beverages to control blood glucose levels and body weight gain. The consumption of NNS has increased in recent years over the world, and many researches have indicated long-term sucralose administration altered the gut microbiome composition of mice. These studies all focus on the US Food and Drug Administration (FDA) defined acceptable daily intake (ADI), approximately 5 mg/kg BW/day for human. In our study, mice were given with T1-4 (0.0003, 0.003, 0.03, and 0.3 mg/mL) of sucralose, respectively, Control group mice were given normal water. In particular, 0.3 mg/mL of sucralose was equal to the ADI (5 mg/kg BW/day). After 16 weeks, all mice were weighted and sacrificed, the liver of each mouse was isolated and weighed, segments of jejunum, ileum and colon were collected for H&E-stained. The contents of jejunum, ileum, cecum and colon were collected for 16S rRNA gene sequencing. The results showed sucralose administration affects the intestinal barrier function evidenced by distinct lymphocyte aggregation in ileum and colon while not change the mice body weight. The 16S rRNA gene sequencing of the mice gut microbiome suggested sucralose administration significantly changed the composition of gut microbiota, especially in T1 and T4 group. For example, a reduction of probiotics abundance (Lachnoclostridium and Lachnospiraceae) was found in cecum of T4 group mice compared with Control group. On the other hand, Allobaculum, which was reported positively correlated with diabetes, was increased in the T1 and T4 group. In addition, the potential pathogens, including Tenacibaculum, Ruegeria, Staphylococcus were also increased in jejunum, ileum and colon by sucralose administration in T1 and T4 group. These new findings indicate that low dose of sucralose (T1) alter gut microbiome in mice, and these adverse health effects are equal to ADI level (T4). Overall, our study provides guidance and suggestions for the use of sucralose in foods and beverages.

DNA Enrichment Methods for Microbial Symbionts in Marine Bivalves

High-throughput sequencing is a powerful tool used for bivalve symbiosis research, but the largest barrier is the contamination of host DNA. In this work, we assessed the host DNA reduction efficiency, microbial community structure, and microbial diversity of four different sample pre-treatment and DNA extraction methods employed in bivalve gill tissue samples. Metagenomic sequencing showed the average proportions of reads belonging to microorganisms retrieved using PowerSoil DNA extraction kit, pre-treatment with differential centrifugation, pre-treatment with filtration, and HostZERO Microbial DNA kit samples were 2.3 ± 0.6%, 2.5 ± 0.2%, 4.7 ± 1.6%, and 42.6 ± 6.8%, respectively. The microbial DNA was effectively enriched with HostZERO Microbial DNA kit. The microbial communities revealed by amplicon sequencing of the 16S rRNA gene showed the taxonomic biases by using four different pre-treatment and DNA extraction methods. The species diversities of DNA samples extracted with the PowerSoil DNA extraction kit were similar, while lower than DNA samples extracted with HostZERO Microbial DNA kit. The results of this study emphasized the bias of these common methods in bivalve symbionts research and will be helpful to choose a fit-for-purpose microbial enrichment strategy in future research on bivalves or other microbe–invertebrate symbioses.

First Isolation of Virulent Tenacibaculum maritimum Isolates from Diseased Orbicular Batfish (Platax orbicularis) Farmed in Tahiti Island

The orbicular batfish (Platax orbicularis), also called ‘Paraha peue’ in Tahitian, is the most important marine fish species reared in French Polynesia. Sudden and widespread outbreaks of severe ‘white-patch disease’ have occurred since 2011 in batfish farms one to three weeks after the transfer of juveniles from bio-secured hatcheries to lagoon cages. With cumulative mortality ranging from 20 to 90%, the sustainability of aquaculture of this species is severely threatened. In this study, we report for the first time the isolation from diseased batfish of several isolates belonging to the species Tenacibaculum maritimum, a major pathogen of many marine fish species. Histopathological analysis, an experimental bath challenge and a field monitoring study showed that T. maritimum is associated with ‘white-patch disease’. Moreover, molecular and serological analyses performed on representative isolates revealed some degree of genetic diversity among the isolates, a finding of primary importance for epidemiological studies and the development of management and control strategies such as vaccination.

Identification of infectious agents in early marine Chinook and Coho salmon associated with cohort survival

Recent decades have seen an increased appreciation for the role infectious diseases can play in mass mortality events across a diversity of marine taxa. At the same time many Pacific salmon populations have declined in abundance as a result of reduced marine survival. However, few studies have explicitly considered the potential role pathogens could play in these declines. Using a multi-year dataset spanning 59 pathogen taxa in Chinook and Coho salmon sampled along the British Columbia coast, we carried out an exploratory analysis to quantify evidence for associations between pathogen prevalence and cohort survival and between pathogen load and body condition. While a variety of pathogens had moderate to strong negative correlations with body condition or survival for one host species in one season, we found that Tenacibaculum maritimum and Piscine orthoreovirus had consistently negative associations with body condition in both host species and seasons and were negatively associated with survival for Chinook salmon collected in the fall and winter. Our analyses, which offer the most comprehensive examination of associations between pathogen prevalence and Pacific salmon survival to date, suggest that pathogens in Pacific salmon warrant further attention, especially those whose distribution and abundance may be influenced by anthropogenic stressors.

Experimental Induction of Tenacibaculosis in Atlantic Salmon (Salmo salar L.) Using Tenacibaculum maritimum, T. dicentrarchi, and T. finnmarkense

There is a limited understanding of the pathogenesis of tenacibaculosis in Atlantic salmon (Salmo salar L.) and there are few reproducible exposure models for comparison. Atlantic salmon were exposed via bath to Tenacibaculum maritimum, T. dicentrarchi, or T. finnmarkense, and were then grouped with naïve cohabitants. Mortalities had exaggerated clinical signs of mouthrot, a presentation of tenacibaculosis characterized by epidermal ulceration and yellow plaques, on the mouth and less frequently on other tissues. Histopathology showed tissue spongiosis, erosion, ulceration, and necrosis ranging from mild to marked, locally to regionally extensive with mats of intralesional bacteria on the rostrum, vomer, gill rakers, gill filaments, and body surface. Exposure to T. maritimum resulted in less than a 0.4 probability of survival for both exposed and cohabitants until Day 21. Exposures to T. dicentrarchi resulted in 0 and 0.55 (exposed), and 0.8 and 0.9 (cohabitant) probability of survival to Day 12 post-exposure, while T. finnmarkense had a 0.9 probability of survival to Day 12 for all groups. This experimental infection model will be useful to further investigate the pathogenesis of tenacibaculosis, its treatment, and immunity to Tenacibaculum species.

Structural and Functional Impacts of Microbiota on Pyropia yezoensis and Surrounding Seawater in Cultivation Farms along Coastal Areas of the Yellow Sea

Pyropia yezoensis is the most important commercial edible red algae in China, carrying a variety of resident microbes at its surface. To understand microbiome diversity, community structure, interactions and functions with hosts in this regard, thalli and seawater sampleswere collected from Yantai and Rizhao cultivation farms in the Yellow Sea. The thalli and seawater samples (n = 12) were collected and studied using an Illumina NovaSeq 6000 platform and 16S ribosomal RNA (rRNA) gene sequencing, along with the consideration of environmental factors. Bacterial communities in association with P. yezoensis and surrounding seawater were predominated by Cyanobacteria, Proteobacteria, and Bacteroidetes. The variability of bacterial communities related to P. yezoensis and seawater were predominantly shaped by nitrate (NO₃), ammonium (NH₄), and temperature. Cluster analysis revealed a close relationship between thalli (RTH and YTH) and seawater (RSW and YSW) in terms of the residing bacterial communities, respectively. PICRUSt analysis revealed the presence of genes associated with amino acid transportation and metabolism, which explained the bacterial dependence on algal-provided nutrients. This study reveals that the diversity of microbiota for P. yezoensis is greatly influenced by abiotic factors and algal organic exudates which trigger chemical signaling and transportation responses from the bacterial community, which in turn activates genes to metabolize subsequent substrates.

Quantitative PCR for Tenacibaculum dicentrarchi and T. finnmarkense

Numerous Tenacibaculum species, including T. dicentrarchi, T. maritimum and T. finnmarkense, are associated with tenacibaculosis in finfish; however, quantitative identification techniques are limited. Quantitative PCR assays were developed to detect T. dicentrarchi and T. finnmarkense. TaqMan assays using 16S rDNA demonstrated low detection limits (0.07-269 bacteria), suitable amplification efficiencies (>86%) and moderate specificity. However, the amplification of isolates with 100% sequence similarity to T. finnmarkense AY7486TD using both the T. finnmarkense and T. dicentrarchi assays indicates that other genes should be investigated. Both assays may help describe the pathogenesis of tenacibaculosis and may aid management practices for the aquaculture industry.

Application of Quantitative-PCR to Monitor Netpen Sites in British Columbia (Canada) for Tenacibaculum Species

Tenacibaculum are frequently detected from fish with tenacibaculosis at aquaculture sites; however, information on the ecology of these bacteria is sparse. Quantitative-PCR assays were used to detect T. maritimum and T. dicentrarchi at commercial Atlantic salmon (Salmo salar) netpen sites throughout several tenacibaculosis outbreaks. T. dicentrarchi and T. maritimum were identified in live fish, dead fish, other organisms associated with netpens, water samples and on inanimate substrates, which indicates a ubiquitous distribution around stocked netpen sites. Before an outbreak, T. dicentrarchi was found throughout the environment and from fish, and T. maritimum was infrequently identified. During an outbreak, increases in the bacterial load in were recorded and no differences were recorded after an outbreak supporting the observed recrudescence of mouthrot. More bacteria were recorded in the summer months, with more mortality events and antibiotic treatments, indicating that seasonality may influence tenacibaculosis; however, outbreaks occurred in both seasons. Relationships were identified between fish mortalities and antimicrobial use to water quality parameters (temperature, salinity, dissolved oxygen) (p < 0.05), but with low R² values (<0.25), other variables are also involved. Furthermore, Tenacibaculum species appear to have a ubiquitous spatial and temporal distribution around stocked netpen sites, and with the potential to induce disease in Atlantic salmon, continued research is needed.