Transport and instream removal of the Cry1Ab protein from genetically engineered maize is mediated by biofilms in experimental streams

Abstract

The majority of maize planted in the US is genetically-engineered to express insecticidal properties, including Cry1Ab protein, which is designed to resist the European maize borer ( Ostrinia nubilalis ). After crop harvest, these proteins can be leached into adjacent streams from crop detritus left on fields. The environmental fate of Cry1Ab proteins in aquatic habitats is not well known. From June-November, we performed monthly short-term additions of leached Cry1Ab into four experimental streams with varying benthic substrate to estimate Cry1Ab transport and removal. At the start of the experiments, when rocks were bare, we found no evidence of Cry1Ab removal from the water column, but uptake steadily increased as biofilm colonized the stream substrate. Overall, Cry1Ab uptake was strongly predicted by measures of biofilm accumulation, including algal chlorophyll a and percent cover of filamentous algae. Average Cry1Ab uptake velocity (v f = 0.059 ± 0.009 mm s -1 ) was comparable to previously reported uptake of labile dissolved organic carbon (DOC; mean v f = 0.04 ± 0.008 mm s -1 ). Although Cry1Ab has been shown to rapidly degrade in stream water, benthic biofilms may decrease the distance proteins are transported in lotic systems. These results emphasize that once the Cry1Ab protein is leached, subsequent detection and transport through agricultural waterways is dependent on the structure and biology of receiving stream ecosystems.

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

“…Based on AICc, the optimal models describing Cry protein remaining were relatively simple and included only DO, ER, and their interaction (AICc = −26.2; log-likelihood = 20.42; Table S7) or ER, DO, and GPP with no interactions (AICc = −25.3; log-likelihood = 19.97; Table S6). We note that all significant stream variables are associated with stream biofilm metabolism, a relationship previously described for the removal of Cry protein in streams water . The strong correlation between Cry concentration and stream metabolism metrics underscores that eProtein degradation in streams is largely mediated by stream function, and likely a result of biological removal.…”

“…This was consistent in both the unfiltered (Figure A; paired t -test between streams and unfiltered jars at 1 h: t = 1.797, df = 18, p = 0.0892) and the filtered treatments (Figure B; paired t -test between streams and filtered jars at 1 h: t = 1.544, df = 18, p = 0.1400), with no difference observed between both jar treatments as well (paired t -test between unfiltered jar vs filtered jar at 1 h: t = 0.3900, df =18, p = 0.7011). Thus, since Cry protein degradation persisted even after the removal of biofilm, it is unlikely that direct biological assimilation drives the removal of Cry proteins in streams in the initial rapid phase, contrary to what was previously thought . Therefore, we suggest that the relationship between Cry protein degradation and stream metabolism was likely due to the indirect effects of stream metabolism on water chemistry, which in turn affected the fate of Cry proteins.…”

“…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. For example, the temperature did not influence Cry protein uptake, and its effect was not tested in our experimental design. However, the temperature may influence the protein concentration in the environment as Cry protein leaching, and consequently input, as well as affect stream metabolism and enzyme activity.…”

“…The 2 day timespan was chosen based on the previous modeling work that predicted most of the protein to be degraded by 48 h . For both experiments, we followed this solar sampling schedule to potentially address the effects of day and night and thus explore the possibility of photodegradation.…”

“…Furthermore, Cry protein has been consistently detected in streams, but research exploring the half-life of these proteins has mainly been done using mesocosm approaches (e.g., Griffiths et al) or assessed in natural soil and groundwater systems. , Degradation of Cry proteins in water is generally rapid, with the majority of the protein degraded within the first 24–48 h after release. , However, much less is known about Cry protein fate in flowing (i.e., lotic) ecosystems, where many abiotic and biotic removal mechanisms can occur simultaneously. By combining modeling and experiments in experimental streams, Shogren et al found a strong relationship between heterotrophic respiration and Cry protein fate, suggesting that biofilm growth mediates the uptake and degradation of Cry proteins in aquatic systems. However, the mechanism responsible for the short half-life of this eProtein in aquatic systems is still unknown.…”