Location: Harry K. Dupree Stuttgart National Aquaculture Research Cntr
2018 Annual Report
Objectives
Objective 1. Characterize the cellular and molecular immune responses governing resistance/susceptibility to infectious disease (Flavobacterium columnare), and develop strategies to enhance immune protection through immunomodulatory compounds, nutritional status, or water chemistry.
Subobjective 1A. Describe the cellular, transcriptional, and pathological responses of mucosal tissues in healthy and Flavobacterium columnare-challenged fish.
Subobjective 1B. Investigate the effects of copper sulfate, short-term feed deprivation, and water chemistry on the mucosal immune system.
Objective 2. Assess microbial community diversity, prevalence, and distribution under homeostatic conditions, after columnaris disease challenge, and following environmental perturbation.
Subobjective 2A. Profile the composition and population dynamics of microbes that reside on the skin and gill of healthy and columnaris-challenged fish.
Subobjective 2B. Investigate the effects of copper sulfate, short-term feed deprivation, and water chemistry on microbial community composition.
Approach
In Objective 1 our research team will utilize next-generation sequencing to establish temporal profiles of transcriptional responses to Flavobacterium (F.) columnare in gill and skin; use flow cytometry to monitor the type and abundance of immune cells trafficking to the gill of challenged fish; and characterize the histopathological changes to an F. columnare challenge and draw parallels to the shifts in immune-related transcripts and cell phenotypes. Studies will also examine the transcriptional and immunological consequences to alterations in water chemistry and to chemical compounds such as copper sulfate. In Objective 2 the core microbiota associated with mucosa in healthy fish and F. columnare infected fish will be characterized using using high-throughput 16S v4 amplicon sequencing. This work will identify the core microbial communities commonly residing in the mucosal barriers of both warmwater bass and channel catfish; vital information towards identifying bacterial species that can be exploited to improve fish health.
Progress Report
ARS researchers have determined that sunshine hybrid striped bass, and its maternal parent white bass, display differences in their susceptibility to the bacterium, Flavobacterium (F.) columnare, whereby hybrid striped bass incurs significantly higher mortality when challenged under laboratory conditions compared to white bass. Studies to evaluate the susceptibility of the paternal parent striped bass and palmetto hybrid striped bass to F. columnare and other bacterial pathogens are ongoing. This research will provide a better understanding of the host-pathogen interactions that are important in the production of Morone spp. in order to improve treatments and aid in the development of disease-resistance genetic markers.
ARS researchers continued their work to characterize factors which stimulate F. columnare biofilms, which are a critical part of the columnaris disease process. Biofilms are an important stage of pathogenesis which requires a sustained host-pathogen interaction at mucosal sites (gill, skin). ARS researchers have identified that skin mucus from different fish species can stimulate the formation of in vitro biofilms. This work has also shown that stimulation of in vivo biofilms with fish mucus causes more substantial mortalities in laboratory disease challenges. ARS researchers continue to conduct studies to better understand the mechanism which activates the biofilm phenotype. This work will help benefit the development of new vaccines and novel therapies to treat infectious diseases.
ARS researchers have recently recognized the importance of the ambient water temperature during the initiation of a mucosal adaptive immune response in the skin. This work characterized the humoral immune response under various environmental temperature conditions including those represented in industry to identify the ideal time and conditions for immunizing catfish fingerlings.
ARS researchers have continued collaborating with researchers in Denmark, Germany, and in the United States to conduct studies which demonstrate the potency of using peracetic acid as a disinfectant in recirculating aquaculture systems. After evaluating research done by ARS researchers, the Environmental Protection Agency (EPA) has approved registration of peracetic acid for use as a disinfectant for aquaculture applications to PeroxyChem, Philadelphia, Pennsylvania and Aquatactics, Kirkland, Washington. ARS researchers will continue their work on the use of peracetic acid as a treatment for fish pathogens in recirculating aquaculture systems.
ARS researchers continued collaborating with researchers at Bowling Green State University, Bowling Green, Ohio and the Freshwater Institute, Shepherdstown, West Virginia, to quantify the amount of aquatic fungus in recirculating aquaculture systems and to treat these systems with peracetic acid to eliminate pathogens.
ARS researchers continued cooperation with researchers at USDA/ARS, Franklin, Maine and the Freshwater Institute, Shepherdstown, West Virginia, to evaluate the safe use of peracetic acid on adult Atlantic salmon or their eggs during spawning. Salmon hatcheries are often plagued by aquatic fungi, and there is a paucity of available treatment methods. Salmon producers are anxiously searching for a replacement for formalin, which many countries are in the process of restricting due to its carcinogenicity.
ARS researchers continued a partnership with researchers at the Department of Mycology, Real Jardín Botánico, Madrid, Spain, on a project focused on the identification of genotypes and establishing the population structure of Saprolegnia parasitica world-wide. This will be the first study to compile a global database of this harmful aquatic pathogen.
Accomplishments
1. Characterization of the Flavobacterium (F.) columnare planktonic and biofilm states through transcriptome analyses. Columnaris disease which is caused by F. columnare severely impacts the production of freshwater finfish species. Due to the impact on the aquaculture industry, research efforts to better understand the biological processes of F. columnare including the formation of biofilms and their contribution to disease are ongoing. ARS researchers at Stuttgart, Arkansas, have identified that catfish mucus activates in vitro biofilm formation of different F. columnare isolates. RNA sequencing of free-living bacterial cells or biofilm cells in the presence of catfish mucus has revealed very different gene expression profiles among these different cell populations. Biofilms show an increase in their gene expression for signal transduction, ligand binding and cell homeostasis pathways. Also as observed in other Gram negative biofilms, there is an up-regulation of iron uptake machinery which is required to accommodate for developing biofilm populations. The current studies to explore the effect of catfish mucus on biofilm development through RNA sequencing will add valuable information about the basic biological processes that occur during the individual planktonic and biofilm states. This work will no doubt serve as a basis for future work on understanding how biofilms are established and how they contribute to disease progression. This will aid in the development of new therapies to treat columnaris disease during the production cycle.
2. Testing of a recombinant protein vaccine to protect catfish against columnaris disease. Flavobacterium (F.) columnare is the causative agent of columnaris disease which severely impacts channel catfish production in the United States. ARS researchers at Stuttgart, Arkansas, had previously identified F. columnare proteins which activate the adaptive immune response. A novel recombinant protein vaccine has been developed resulting in excellent immune protection against columnaris disease. ARS researchers at Stuttgart, Arkansas have shown over two consecutive years of experimental vaccine trials that the use of the recombinant protein as an immunogen provides significant protection during laboratory disease challenges. Research on optimization and development of a current vaccine to prevent columnaris disease in catfish is ongoing.
Review Publications
Liu, D., Straus, D.L., Pedersen, L., Meinelt, T. 2017. Periodic bacterial control with peracetic acid in a recirculating aquaculture system and its long-term beneficial effect on fish health. Aquaculture. 485:154-159.
Lange, M.D., Webster, C.D. 2017. The effect of temperature on the mucosal IgM antibody response to DNP-KLH in channel catfish (Ictalurus punctatus). Fish and Shellfish Immunology. 70:493-497.
Gesto, M., Liu, D., Pedersen, L., Meinelt, T., Straus, D.L., Jokumsen, A. 2018. Confirmation that pulse and continuous peracetic acid administration does not disrupt the acute stress response in rainbow trout. Aquaculture. 492:190-194.
Zhang, D., Beck, B.H., Mohammed, H., Zhao, H., Thongda, W., Ye, Z., Zeng, Q., Shoemaker, C.A., Fuller, S.A., Peatman, E. 2018. L-rhamnose-binding lectins (RBLs) in Nile tilapia, Oreochromis niloticus: characterization and expression profiling in mucosal tissues. Fish and Shellfish Immunology. 72:426-435.
Straus, D.L., Ledbetter, C.K., Farmer, B.D., Liu, D., Meinelt, T. 2017. Toxicity of peracetic acid to various species of fish. Journal of the World Aquaculture Society. https://doi.org/10.1111/jwas.12475.
