Persistence of detectable insecticidal proteins from Bacillus thuringiensis (Cry) and toxicity after adsorption on contrasting soils

• Published in: Environmental pollution (1987) 2016-01, Vol.208 (Pt B), p.318-325
• Main Authors: Hung, T.P., Truong, L.V., Binh, N.D., Frutos, R., Quiquampoix, H., Staunton, S.
• Format: Article
• Language: English
• Subjects: Adsorption; Animals; Bacillus thuringiensis; Bacterial Proteins - analysis; Bacterial Proteins - toxicity; Crops, Agricultural - metabolism; Earth Sciences; Endotoxins - metabolism; Environmental Monitoring; Geochemistry; Hemolysin Proteins - metabolism; Insecta - metabolism; Insecticides - analysis; Insecticides - toxicity; Larva - metabolism; Manduca; Persistence; Pesticide Residues - analysis; Pesticide Residues - toxicity; Sciences of the Universe; Soil; Soil - chemistry; Soil Microbiology; Toxicity
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2015.09.046

Insecticidal Cry, or Bt, proteins are produced by the soil-endemic bacterium, Bacillus thuringiensis and some genetically modified crops. Their environmental fate depends on interactions with soil. Little is known about the toxicity of adsorbed proteins and the change in toxicity over time. We incubated Cry1Ac and Cry2A in contrasting soils subjected to different treatments to inhibit microbial activity. The toxin was chemically extracted and immunoassayed. Manduca sexta was the target insect for biotests. Extractable toxin decreased during incubation for up to four weeks. Toxicity of Cry1Ac was maintained in the adsorbed state, but lost after 2 weeks incubation at 25 °C. The decline in extractable protein and toxicity were much slower at 4 °C with no significant effect of soil sterilization. The major driving force for decline may be time-dependent fixation of adsorbed protein, leading to a decrease in the extraction yield in vitro, paralleled by decreasing solubilisation in the larval gut. Biotest, presenting Cry-contaminated feed to Manduca sexta larvae in individual Perspex boxes. [Display omitted] •Toxicity of Cry protein is initially conserved after adsorption on soil.•Toxicity and extractability decline with time, more rapidly at 25 °C than 4 °C.•Similar dynamics of Cry1AC and Cry2A on soil with varying texture and organic C.•Sterilization of soil does not change Cry dynamics or temperature effect in soil.•Cry decline is determined by progressive fixation on soil not microbial breakdown. Toxicity was initially maintained after adsorption on soil and both extractable Cry and toxicity declined rapidly, more slowly at low temperature, due to different fixation dynamics. Toxicity of Cry protein is initially conserved after adsorption on soil.