Location: Aquatic Animal Health Research
Project Number: 6010-32000-027-014-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 1, 2020
End Date: Jun 30, 2025
Problem: The catfish industry, comprised of channel and hybrid catfish, is the largest sector of US aquaculture ($360 million in foodsize catfish 2018). Flavobacterium columnare, the causative agent of columnaris disease produces substantial mortality during the production of freshwater farmed finfish species. According to the 2010 USDA National Animal and Health Monitoring System statistics, this bacterium remains one of the top disease issues among catfish production accounting for 40% of fish losses. F columnare is ubiquitous in the aquatic environment and is often triggered during the summer months during the production cycle. As food fish production continues to increase, the frequency of columnaris disease will only continue to rise within the aquaculture industry. Add to this an increase in the regulation of treatments and resistance to available antibiotics means that alternative methods of disease protection will be required. Vaccination is one potential strategy to reduce the impact of columnaris disease; however, this has proven to be difficult. In the last two years we have vaccinated catfish with a recombinant F columnare DnaK protein, and we have shown > 60% survival in fish vaccinated with DnaK protein compared to only 30% survival in non-vaccinated fish after F columnare laboratory challenges (Lange, Beck et al. 2016, Lange, Abernathy et al. 2019). Another potential approach is feed-based interventions to minimize or protect animals from columnaris disease. Accordingly, our research team has identified probiotic strains that exert cytotoxic effects to F columnare in vitro. In our initial study we evaluated a large collection of bacterial isolates to identify those that were able to inhibit the in vitro growth of F columnare, Aeromonas hydrophila, Edwardsiella ictaluri and/or other fish pathogens (Ran et al., 2012). Our bestperforming probiotic strain Bacillus velezensis AP193 has been observed to be effective at reducing mortality in tilapia due to virulent A. hydrophila (Addo et al., 2017) or Streptococcus iniae (Addo et al., 2017). We have also conducted a replicated pond study with control feed vs. AP193-fed fish (Thurlow et al., 2019) showing probiotic-mediated enhanced catfish growth and reduced N and Pin pond water. Fish fed with strain AP193 spores in aquaria had a mean 14 % increase in growth compared to control fish, which was better growth performance enhancement compared to the other Bacillus spp. While these studies show that the probiotic B. velezensis AP193 has beneficial effects on catfish growth and disease control, their use to control columnaris disease in vivo has not yet been explored, nor has any synergy with vaccination been evaluated. The goals of this project are to determine the extent to which the feeding of probiotic strain B. velezensis AP193: 1) enhance protection against laboratory challenges with F columnare; 2) impact host microbial communities (through metagenomic profiling); 3) act as immumodulators to improve the efficacy of a recombinant protein columnaris vaccine developed by our research team.
Cooperator proposes to provide ARS scientists with probiotic formulations of B. velezensis AP193. ARS scientists will collaborate with Dr. Mark Liles (School of Fisheries, Auburn University), to perform trials which will include the addition of the probiotic to stock catfish diets. Example comparisons include the evaluation of columnaris disease resistance in na'fve control fish, probiotic fed fish, vaccinated fish, and those receiving both probiotic and vaccine. Relevant endpoints include survival, the characterization of the commensal microbial compartment in relevant mucosal tissues through metatranscriptomic and microbiome (i.e. 16S rRNA gene amplicon sequencing) analyses, and humeral and cellular adaptive phenotyping.