Short communication: The rate of release of Cry1Ab protein from Bt maize leaves into water

Abstract

Transgenic Bt maize plants are genetically modified to contain genes of Bacillus thuringiensis that encode for δ-endotoxins (Cry1Ab protein) that have insecticidal properties. These endotoxins target certain lepidopteran pests of maize. There are several entry routes by which Cry proteins enter the aquatic ecosystem in which aquatic organisms are exposed to these proteins. The main route is through plant debris such as leaves, stalks and postharvest detritus that are transported by means of run-off, rain and wind. While several studies have been conducted on the fate of Cry1Ab protein in terrestrial ecosystems, little is known of the release rates of Cry1Ab proteins from maize plant tissues that end up in aquatic ecosystems. In this study, leaves of Bt-maize and its isoline were submerged in containers filled with deionised or borehole water for a period of 16 days, and kept at 3 different temperatures (10±1, 21±1 and 30±1°C). Samples were collected at 1, 2, 4, 8, 16, 24, 48, 96, 192 and 384 h post submersion and analysed for Cry protein content using enzyme-linked immunosorbent assay (ELISA). The release of Cry protein from submerged maize leaves was influenced by temperature, and duration of immersion. An increase in Cry protein levels in the water was observed from the first hour onwards in both water types until the end of the experiment. The highest concentration of Cry protein was found at 30°C. This study showed that temperature and time period influence the release rate of Cry proteins from dried leaf matter into the aquatic environment.

Fate of Environmental Proteins (eProteins) from Genetically Engineered Crops in Streams is Controlled by Water pH and Ecosystem Metabolism

“…Nonetheless, documented nontarget impacts of Bt-Cry happen at chronic exposure , or at concentrations many orders of magnitude higher than the persistent ones . Thus, the downstream concentrations of Cry protein are likely to be diluted, but upstream regions that are near direct inputs may be where concentrations are highest, and where the impact of Cry proteins should be closely monitored. , However, as Bt maize detritus travels downstream in the watershed and leaches the protein along the way for several days, the predicted range of impact may increase, as higher protein concentrations could be observed downstream if there is a traveling source. , Accordingly, management techniques that stop detritus from entering waterways, such as protection of riparian vegetation and buffer strips along field edges, may be highly effective in limiting the input and impact of Cry protein to adjacent aquatic ecosystems, especially at the local scale.…”

“…Additionally, this approach simplified the input/degradation dynamics in the system and avoided the potential influence of variables in Cry protein leaching/input. Previous work has been ambiguous regarding the dynamics of Cry proteins leaching from maize detritus, , likely due to differences in maize variety, tissue, substrate used, and water chemistry. Therefore, although the results here are relevant for understanding the impact of the protein, it is important to note that there are numerous additional variables determining the synchronous Cry protein input and degradation in natural systems.…”

“…Overall, the degradation profile observed here confirms the status of Cry protein as a pseudopersistent compound and reinforces that efforts to contain Bt maize detritus on fields are potentially effective in limiting the potential input of Cry protein to adjacent waterways. 22,23,26,27 Finally, because proteins have highly variable conformations, functions, and chemical properties, it is unlikely that the degradation profile observed here for Cry protein can be extrapolated to all eProteins. However, it is likely that the same mechanisms will be relevant in some cases and this research could guide further explorations of eProtein fate.…”

“…The major source of Cry proteins in natural systems is crop detritus, ,, therefore we used maize detritus (origin: Texas A&M Field Laboratory, Burleson County, TX) as a source of Cry proteins for this experiment. This material was of the variety Dekalb DKC67-42 (Dekalb Genetics Corp., Dekalb, IL), which expresses two Cry protein proteins, Cry1A.105 and Cry2Ab2.…”

“…Accordingly, Cry protein is seasonally detectable in streams that drain agricultural fields, varying with crop growth and harvesting cycles from 0 to over 100 ng/L . These streams are subject to Cry protein input from various sources, , including Bt maize leaf litter in the soil profile, root exudates that leach into streams or degradation of detritus, and pollen that is transported into adjacent streams by runoff ,− and wind…”