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Interactions between Bacillus thuringiensis subsp. israelensis and Fathead Minnows, Pimephales promelas Rafinesque,
1Environmental Research Laboratory-Duluth, U.S. Environmental Protection Agency, 6201 Congdon Boulevard, Duluth, Minnesota 55804.
Abstract:
Interactions between Bacillus thuringiensis subsp. israelensis and fathead minnows, Pimephales promelas, were studied in laboratory exposures to two commercial formulations, Vectobac-G and Mosquito Attack. Mortality among fatheads exposed to 2.0 x 10 to 6.5 x 10 CFU/ml with both formulations was attributed to severe dissolved oxygen depletion due to formulation ingredients rather than to direct toxicity from the parasporal crystal. No adverse effects were observed at 6.4 x 10 CFU/ml and below. Fathead minnows rapidly accumulated high numbers of spores with 1 h of exposure to 2.2 x 10 CFU of Mosquito Attack per ml, producing whole-body counts of 4.0 x 10 CFU per fish. Comparison of counts on gastrointestinal tract samples and whole-body samples and high numbers of spores in feces indicated that ingestion was the major route of exposure. B. thuringiensis subsp. israelensis spore counts decreased rapidly after transfer of fish to clean water, with a drop of over 3 orders of magnitude in 1 day. Spores were rarely detected in fish after 8 days but were detectable in feces for over 2 weeks. These findings suggest that fish could influence the dissemination of B. thuringiensis subsp. israelensis, and possibly other microbial agents, in the aquatic environment.
Insights
Bacillus thuringiensis subsp. israelensis (Bt israelensis) exposure caused no direct toxicity to fathead minnows. Fish ingested spores, potentially disseminating Bt israelensis in aquatic environments.
Area of Science:
- Environmental Toxicology
- Aquatic Ecology
- Microbial Ecology
Background:
- Bacillus thuringiensis subsp. israelensis (Bt israelensis) is a microbial larvicide used for mosquito control.
- Understanding non-target effects on aquatic organisms like fathead minnows (Pimephales promelas) is crucial for ecological risk assessment.
- Commercial formulations may contain ingredients that impact aquatic environments.
Purpose of the Study:
- To investigate the interaction between Bt israelensis and fathead minnows.
- To determine the toxicity and exposure routes of Bt israelensis in fathead minnows.
- To assess the potential for fish to disseminate Bt israelensis in aquatic ecosystems.
Main Methods:
- Laboratory exposures of fathead minnows to two commercial Bt israelensis formulations (Vectobac-G, Mosquito Attack).
- Monitoring of fish mortality and dissolved oxygen levels.
- Quantification of Bt israelensis spore accumulation in whole bodies, gastrointestinal tracts, and feces.
- Tracking spore clearance from fish tissues and feces after transfer to clean water.
Main Results:
- Mortality was linked to dissolved oxygen depletion from formulation ingredients, not direct Bt israelensis toxicity.
- Fathead minnows rapidly ingested high concentrations of Bt israelensis spores (up to 4.0 x 10^6 CFU/fish).
- Ingestion was the primary exposure route, with spores detectable in feces for over two weeks post-exposure.
Conclusions:
- Bt israelensis commercial formulations can cause indirect harm to fathead minnows via oxygen depletion.
- Fathead minnows can act as vectors for Bt israelensis dissemination in aquatic environments.
- Fish play a role in the environmental fate and spread of microbial agents.
