Functional effects of the bacterial insecticide Bacillus thuringiensis var. kurstaki on aquatic microbial communities

• Published in: Ecotoxicology and environmental safety 1996-04, Vol.33 (3), p.271-280
• Main Authors: KREUTZWEISER, D. P, GRINGORTEN, J. L, THOMAS, D. R, BUTCHER, J. T
• Format: Article
• Language: English
• Subjects: ambiente acuatico; Analysis of Variance; Animal, plant and microbial ecology; Animals; Applied ecology; aquatic environment; Bacillus thuringiensis; Bacillus thuringiensis - cytology; Bacillus thuringiensis - metabolism; Bacillus thuringiensis kurstaki; Bacteria - growth & development; Bacteria - metabolism; betula alleghaniensis; bioassays; Biodegradation, Environmental; Biofilms; Biological and medical sciences; Biological Assay; choristoneura fumiferana; Colony Count, Microbial; degradacion; degradation; densidad de la poblacion; densite de population; Discriminant Analysis; dosage biologique; Ecotoxicology, biological effects of pollution; efectos secundarios; effet secondaire; ensayo biologico; Eukaryota - drug effects; feuille; formulaciones; formulation; formulations; Fresh water environment; Freshwater; Fundamental and applied biological sciences. Psychology; hojas; Larva; leaves; Lepidoptera; Lethal Dose 50; Linear Models; microorganisme; microorganismos; microorganisms; milieu aquatique; Oxygen Consumption; Pest Control, Biological; Plant Leaves - metabolism; Plant Leaves - microbiology; Plant Leaves - parasitology; population density; Protein-Tyrosine Kinases - toxicity; protozoa; Random Allocation; side effects; trichoplusia ni; Water Microbiology
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1006/eesa.1996.0035

Epilithic microbial communities were colonized on leaf disks and exposed to commercial preparations of Bacillus thuringiensis var. kurstaki (Btk) in aquatic microcosms. Responses in terms of microbial respiration, bacterial cell density, protozoan density, and microbial decomposition activity were measured. Test concentrations for treatments with Dipel 64AF and Dipel 8AF in microcosms were the expected environmental concentration (EEC) of 20 IU/ml, 100x the EEC, and 1000x the EEC. Bacterial cell density in the biofilm of leaf disks was significantly increased at concentrations as low as the EEC. There were no concomitant alterations in protozoan density. Microbial respiration was significantly increased, and decomposition activity was significantly decreased, but only at the artificially high concentration of 1000x the EEC. This effect was attributed to the spore-crystal component rather than formulation ingredients. Microbial decomposition of leaf material was also determined in outdoor stream channels treated at concentrations ranging from the EEC to 100x the EEC. Although there tended to be reduced decomposition activity in treated channels, there were no significant differences in mass loss of leaf material between treated and control channels. Various regression, classification, and ordination procedures were applied to the experimental data, and none indicated significant treatment effects. These results from laboratory and controlled field experiments indicate that contamination of watercourses with Btk is unlikely to result in significant adverse effects on microbial community function in terms of detrital decomposition.