FIRST ISOLATION OF TENACIBACULUM MARITIMUM IN A CAPTIVE SAND TIGER SHARK (CARCHARIAS TAURUS)

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.

Elasmobranch-associated microbiota: a scientometric literature review

Elasmobranchs provide greatly relevant ecosystem services for the balance of the environments in which they are inserted. In recent decades, sharp population declines have been reported for many species in different regions worldwide, making this taxonomic group currently one of the most threatened with extinction. This scenario is almost entirely due to excessive fishing pressure, but any contributing factor that may cause additional mortality to populations must be mapped and monitored. In a fast-changing world, emerging marine pollution associated with climate change display the potential to increase the spread of infectious agents. These can, in turn, lead to mortality events, both directly and indirectly, by reducing immune responses and the physical and nutritional condition of affected individuals. In this context, the present study aimed to analyze data concerning elasmobranch-associated microbiota, identifying study trends and knowledge gaps in order to direct future studies on this topic of growing relevance for the health of wild populations, as well as individuals maintained in captivity, considering the zoonotic potential of these microorganisms.

Roseobacter group probiotics exhibit differential killing of fish pathogenic Tenacibaculum species

Fish pathogenic bacteria of the Tenacibaculum genus are a serious emerging concern in modern aquaculture, causing tenacibaculosis in a broad selection of cultured finfish. Data describing their virulence mechanisms are scarce and few means, antibiotic treatment aside, are available to control their proliferation in aquaculture systems. We genome sequenced a collection of 19 putative Tenacibaculum isolates from outbreaks at two aquaculture facilities and tested their susceptibility to treatment with tropodithietic acid (TDA)-producing Roseobacter group probiotics. We found that local outbreaks of Tenacibaculum can involve heterogeneous assemblages of species and strains with the capacity to produce multiple different virulence factors related to host invasion and infection. The probiotic Phaeobacter piscinae S26 proved efficient in killing pathogenic Tenacibaculum species such as T. maritimum, T. soleae, and some T. discolor strains. However, the T. mesophilum and T. gallaicum species exhibit natural tolerance towards TDA and are hence not likely to be easily killed by TDA-producing probiotics. Tolerance towards TDA in Tenacibaculum is likely involving multiple inherent physiological features pertaining to electron and proton transport, iron sequestration, and potentially also drug efflux mechanisms, as genetic determinants encoding such features were significantly associated with TDA tolerance. Collectively, our results support the use of TDA-producers to prevent tenacibaculosis, however, their efficacy is likely limited to some Tenacibaculum species. Importance A productive and sustainable aquaculture sector is needed to meet the UN sustainable development goals (SDGs) and supply the growing world population with high-protein food sources. A sustainable way to prevent disease outbreaks in the industry is the application of probiotic bacteria that can antagonize fish pathogens in the aquaculture systems. TDA-producing Roseobacter group probiotics have proven efficient in killing important vibrio pathogens and protecting fish larvae against infection, yet their efficacy against different fish pathogenic species of the Tenacibaculum genus has not been explored. Therefore, we tested the efficacy of such potential probiotics against a collection of different Tenacibaculum isolates and found the probiotic to efficiently kill a subset of relevant strains and species, supporting their use as sustainable disease control measure in aquaculture.

Advancements in Characterizing Tenacibaculum Infections in Canada

Tenacibaculum is a genus of gram negative, marine, filamentous bacteria, associated with the presence of disease (tenacibaculosis) at aquaculture sites worldwide; however, infections induced by this genus are poorly characterized. Documents regarding the genus Tenacibaculum and close relatives were compiled for a literature review, concentrating on ecology, identification, and impacts of potentially pathogenic species, with a focus on Atlantic salmon in Canada. Tenacibaculum species likely have a cosmopolitan distribution, but local distributions around aquaculture sites are unknown. Eight species of Tenacibaculum are currently believed to be related to numerous mortality events of fishes and few mortality events in bivalves. The clinical signs in fishes often include epidermal ulcers, atypical behaviors, and mortality. Clinical signs in bivalves often include gross ulcers and discoloration of tissues. The observed disease may differ based on the host, isolate, transmission route, and local environmental conditions. Species-specific identification techniques are limited; high sequence similarities using conventional genes (16S rDNA) indicate that new genes should be investigated. Annotating full genomes, next-generation sequencing, multilocus sequence analysis/typing (MLSA/MLST), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), and fatty acid methylesters (FAME) profiles could be further explored for identification purposes. However, each aforementioned technique has disadvantages. Since tenacibaculosis has been observed world-wide in fishes and other eukaryotes, and the disease has substantial economic impacts, continued research is needed.

The Complete Genome Sequence of the Fish Pathogen Tenacibaculum maritimum Provides Insights into Virulence Mechanisms

Tenacibaculum maritimum is a devastating bacterial pathogen of wild and farmed marine fish with a broad host range and a worldwide distribution. We report here the complete genome sequence of the T. maritimum type strain NCIMB 2154^T. The genome consists of a 3,435,971-base pair circular chromosome with 2,866 predicted protein-coding genes. Genes encoding the biosynthesis of exopolysaccharides, the type IX secretion system, iron uptake systems, adhesins, hemolysins, proteases, and glycoside hydrolases were identified. They are likely involved in the virulence process including immune escape, invasion, colonization, destruction of host tissues, and nutrient scavenging. Among the predicted virulence factors, type IX secretion-mediated and cell-surface exposed proteins were identified including an atypical sialidase, a sphingomyelinase and a chondroitin AC lyase which activities were demonstrated in vitro.