Comparison of the affinity and extraction yield of trace amounts of three Cry proteins from Bacillus thuringiensis in contrasting types of soil

Abstract

Summary The use of insecticidal proteins known as Cry or Bt, either as biopesticides used in agriculture or as vector control or originating from commercial genetically modified crops (GM), is increasing rapidly. The fate of these proteins in the environment depends strongly on their adsorption on the organo–mineral complexes of soil. Environmental monitoring requires the quantification of the proteins and this entails their chemical extraction from soil. Three Cry proteins, Cry1Ac, Cry1C and Cry2A, present in commercial biopesticide formulations or synthesized by GM plants or both were studied. The adsorption of trace amounts of Cry proteins on over 40 types of soil with contrasting properties was measured in dilute suspension. After a short incubation the extraction yield was measured with a previously tested alkaline solution that contained surfactant and another protein. Each of the proteins had a strong affinity for soil. No soil property was observed to determine either the affinity for soil or the extraction yield. There was no simple relation between the affinity (assessed from the distribution coefficient, Kd) and the extraction yield, although there was a significant inverse relation (P < 0.05) for two of the proteins, Cry1Ac and Cry2A. The proteins differ in both their affinity for soil and their extraction yields. We conclude that these insecticidal proteins will be largely immobile in soil, but that routine environmental monitoring can give only semi‐quantitative values for protein in soil.

Fate of insecticidalBacillus thuringiensisCry protein in soil: differences between purified toxin and biopesticide formulation

“…The sterile nutrient solution was composed of 500 µM of MgSO 4 , 10 µM of MnSO 4 , 50 µM of ZnSO 4 , 50 µM of Fe 2 (SO 4 ) 3 , 1 mM of CaCl 2 , 50 mM of KH 2 PO 4 , 30 μL L −1 of H 2 SO 4 , 7.5 g L −1 of bacteriological peptone (Sigma P0556; Merck‐Lfe Sciences, Darmstadt, Germany) and 1% glucose at pH 7.4. The protoxin was solubilised and enzymatically truncated, and the resulting Cry1Ac toxin was purified as previously described . The protein solution was stored at 4 °C in 3‐(cyclohexylamino)‐1‐propanesulfonic acid (CAPS) buffer at pH 10.4 containing 350 mM of NaCl to avoid oligomerisation of the protein.…”

“…Although the solubilisation of crystals in soils may be slow, given that soil pH is rarely strongly alkaline, crystals will eventually be solubilised and truncated. As for other proteins, soluble Cry proteins released into soil are rapidly adsorbed on soil organomineral surfaces . Adsorbed proteins are largely immobilised, and adsorption has various consequences.…”

Beneficial services of Glomalin and Arbuscular Mycorrhizal fungi in degraded soils in Brazil

“…The total soil protein related to glomalin (T-GRSP) is the sum of EE-GRSP and DE-GRSP. A recent study (Staunton et al, 2020) refutes this hypothesis that the easily extractable fraction is more recent compared to the total fraction, also highlighting that for complex surfaces such as soils, it is difficult to separate the effects of fixation which depends on the time that makes extraction less efficient, protein breakdown and loss of biological or biochemical activity (Hung et al, 2015). On the other hand, Staunton et al (2020) support the fact that GRSP is not just the source of arbuscular mycorrhizal fungi.…”

Environmental Fate of Insecticidal Plant-Incorporated Protectants from Genetically Modified Crops: Knowledge Gaps and Research Opportunities

“…Low extraction efficiencies of PIPs from environmental samples typically reflect a high affinity of the PIP to particle surfaces in the sample . Extraction efficiencies for both Cry proteins and dsRNA are typically low (10–50%) from clayey and silty soils and sediments and higher (75–120%) from sandy materials. ,− While harsher extraction conditions may facilitate PIP desorption, these conditions may alter the PIP molecule and therefore be incompatible with the intended detection method.…”