Abstract
Determining the influence of soil environmental factors on degradation of Cry1Ac protein from Bt cotton residues is vital for assessing the ecological risks of this commercialized transgenic crop. In this study, the degradation of Cry1Ac protein in leaves and in buds of Bt cotton in soil was evaluated under different soil water content and temperature settings in the laboratory. An exponential model and a shift-log model were used to fit the degradation dynamics of Cry1Ac protein and estimate the DT50 and DT90 values. The results showed that Cry1Ac protein in the leaves and buds underwent rapid degradation in the early stage (before day 48), followed by a slow decline in the later stage under different soil water content and temperature. Cry1Ac protein degraded the most rapidly in the early stage at 35°C with 70% soil water holding capacity. The DT50 values were 12.29 d and 10.17 d and the DT90 values were 41.06 d and 33.96 d in the leaves and buds, respectively. Our findings indicated that the soil temperature was a major factor influencing the degradation of Cry1Ac protein from Bt cotton residues. Additionally, the relative higher temperature (25°C and 35°C) was found to be more conducive to degradation of Cry1Ac protein in the soil and the greater water content (100%WHC) retarded the process. These findings suggested that under appropriate soil temperature and water content, Cry1Ac protein from Bt cotton residues will not persist and accumulate in soil.
Highlights
The cultivation of Bacillus thuringiensis crops has raised public concerns on their risk to nontarget organisms
Cry protein expressed exogenously in transgenic Bt (Bacillus thuringiensis) crops can enter into the soil ecosystem after secretion by crop roots [1,2,3,4,5,6], crop aboveground and post-harvest residues returning to soil [7,8,9], and pollen dissemination [10]
Donegan et al [21] reported that the purified protein from Bacillus thuringiensis subsp. kurstaki and the Cry1Ac protein from Bt cotton persisted at detectable levels as measured by enzyme-linked immunosorbent assay (ELISA) for up to 28 and 56 d in soil, respectively
Summary
The cultivation of Bacillus thuringiensis crops has raised public concerns on their risk to nontarget organisms. Cry protein expressed exogenously in transgenic Bt (Bacillus thuringiensis) crops can enter into the soil ecosystem after secretion by crop roots [1,2,3,4,5,6], crop aboveground and post-harvest residues returning to soil [7,8,9], and pollen dissemination [10]. Once it enters the soil, Cry protein is rapidly absorbed and bound on surface-active particles, including clay minerals, humic acids, and complexes of montmorillonite-humic acids-Al hydroxypolymers [11,12,13,14,15,16,17]. Other factors (such as soil properties, microbes, water content, pH, and temperature) were found to have impact on the degradation of Cry protein in soil [19, 20, 28,29,30,31]
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