Occurrence, leaching, and degradation of Cry1Ab protein from transgenic maize detritus in agricultural streams

Ca and Mg stimulate protein synthesis in maize kernel through the action of endogenous hormones and defense enzymes

Soil calcium (Ca) and magnesium (Mg) mineral states in rain-fed arid regions of Northwest China are inefficient, and their levels of substitution and water-soluble states are far below the lowest threshold required for maize growth, resulting in frequent physiological diseases, restricting synthesis of kernel protein (CRP). Our study set up different levels of foliar spraying of Ca and Mg fertilizers before maize pollination to examine the response characteristics of physiological and biochemical indicators in kernel, and the driving process of CRP synthesis. The main findings were: (1) Ca and Mg significantly increased the levels of CRP and endogenous hormones, and the activities of defense enzymes and CRP synthesis enzymes, which decreased significantly and stabilized at the maturity stage of maize. (2) The synthesis and accumulation of CRP were synergistically regulated by endogenous hormones, defense enzymes, and CRP synthase enzymes, with the degree of regulation varying with the level of Ca and Mg supplementation. Indole-3-acetic acid (IAA), gibberellin (GA), zeatin riboside (ZR), catalase (CAT), malondialdehyde (MDA), and glutamate dehydrogenase (GDH) were the primary physiological driving indicators of CRP synthesis, with CRP having a significant synergistic relationship with CAT and a remarkable trade-off with other driving indicators. (3) The dominant driving pathway of CRP synthesis was "Ca, Mg-IAA or GA or ZR-CAT-GDH-CRP". Ca and Mg positively affected IAA and GA levels, and IAA and GA positively regulated CAT activity. However, CAT negatively regulated GDH levels, causing GDH to negatively influence the synthesis and accumulation of CRP and its components. The findings provide theoretical support for further study of inter-root endogenous hormones and soil microbe-driven processes in the regulation of maize quality by Ca and Mg.

Assessing Effects of Genetically Modified Plant Material on the Aquatic Environment Using higher-tier Studies

Genetically modified organisms are used extensively in agriculture. To assess potential side effects of genetically modified (GM) plant material on aquatic ecosystems, only a very small number of higher-tier studies have been performed. At the same time, these studies are particularly important for comprehensive risk assessment covering complex ecological relationships. Here we evaluate the methods of experimental higher-tier effect studies with GM plant material (or Bt toxin) in comparison to those well-established for pesticides. A major difference is that nominal test concentrations and thus dose-response relationships cannot easily be produced with GM plant material. Another important difference, particularly to non-systemic pesticides, is that aquatic organisms are exposed to GM plant material primarily through their feed. These and further differences in test requirements, compared with pesticides, call for a standardisation for GM-specific higher-tier study designs to assess their potentially complex effects in the aquatic ecosystems comprehensively.

Climate change did not alter the effects of Bt maize on soil Collembola in northeast China

Bt maize is being increasingly cultivated worldwide as the effects of climate change are increasing globally. Bt maize IE09S034 and its near-isogenic non-Bt maize Zong 31 were used to investigate whether climate change alters the effects of Bt maize on soil Collembola. Warming and drought conditions were simulated using open-top chambers (OTC), and their effects on soil Collembola were evaluated. We found that the maize type had no significant effect on Collembola; however, the abundance and diversity of Collembola were significantly higher in the OTC than outside at the seedling stage; they were significantly lower in the OTC at the heading and mature stages. The interactions of the maize type with the OTC had no effect on these parameters. Therefore, Bt maize had no significant effect on soil Collembola, and the effects of climate warming and drought on soil Collembola depended on the ambient climatic conditions. When the temperature was low, collembolan abundance and diversity were promoted by warming; however, when the temperature was high and the humidity was low, collembolan abundance and diversity were inhibited by warming and drought. The climate changes simulated by the OTC did not alter the effects of Bt maize on soil Collembola.

Novel Field-Based Protein Detection Method Using Light Transmission Spectroscopy and Antibody Functionalized Gold Nanoparticles

Protein detection is a universal tool critical to many applications in medicine, agriculture, and biotechnology. We developed a novel protein detection method combining light transmission spectroscopy and particle-size analysis of gold nanospheres monovalently functionalized with polyclonal antibodies and applied it to an emerging challenge for such technologies─the monitoring of environmental proteins (eProteins) present in natural aquatic systems. These are an underreported source of pollution and include the pseudopersistent Cry toxins that enter aquatic ecosystems from surrounding genetically engineered crops. The assay is capable of detecting proteins in complex matrices, such as water samples collected in the field, making it a competitive assay for eProtein detection. It is sensitive, reaching 1.25 ng mL^-1, and we demonstrate its application to the detection of Cry1Ab from subsurface tile-drain and streamwater samples from agricultural waterways. The assay can also be quickly adapted for other protein detection applications in the future.

Environmental fate of Bt proteins in soil: Transport, adsorption/desorption and degradation

During the production and application of Bacillus thuringiensis (Bt) transgenic crops, large doses of insecticidal Bt toxic proteins are expressed continuously. The multi-interfacial behaviors of Bt proteins entering the environment in multi-media affects their states of existence transformation, transport and fate as well as biological and ecological impacts. Because both soil matrix and organisms will be exposed to Bt proteins to a certain extent, knowledge of the multi-interfacial behaviors and affecting factors of Bt proteins are vital not only for understanding the source-sink distribution mechanisms, predicting their bio-availability, but also for exploring the soil safety and environmental problems caused by the interaction between Bt proteins and soil matrix. This review summarized and analyzed various internal and external factors that affect the adsorption/ desorption and degradation of Bt proteins in the environment, so as to understand the multi-interfacial behaviors of Bt proteins. In addition, the reasons of concentration changes of Bt proteins in soil are discussed. This review will also discuss the existing knowledge of the combined effects of Bt proteins and other pollutants in environment. Finally, discussing the factors that should be considered when assessing the environmental risk of Bt proteins, thus to further improve the understanding of the environmental fate of Bt proteins.

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

Environmental proteins (eProteins), such as Cry proteins associated with genetically engineered (GE) organisms, are present in ecosystems worldwide, but only rarely reach concentrations with detectable ecosystem-level impacts. Despite their ubiquity, the degradation and fate of Cry and other eProteins are mostly unknown. Here, we report the results of an experiment where we added Cry proteins leached from GE Bt maize to a suite of 19 recirculating experimental streams. We found that Cry exhibited a biphasic degradation with an initial phase of rapid and variable degradation within 1 h, followed by a slow and steady phase of degradation with traces of protein persisting after 48 h. The initial degradation was correlated with heterotrophic respiration and water column dissolved oxygen, confirming a previously documented association with stream metabolism. However, protein degradation persisted even with no biofilm and was faster at a more acidic pH, suggesting that water chemistry is also a critical factor in both degradation and subsequent detection. We suggest that Cry, as well as other eProteins, will have a rapid degradation caused by denaturation of proteins and pH changes, which confirms that the detection of Cry proteins in natural streams must be the result of steady and consistent leaching into the environment.

Bt Proteins Exacerbate Negative Growth Effects in Juvenile Rusty (F. rusticus) Crayfish Fed Corn Diet

The adoption of genetically modified (GM) crops has occurred rapidly in the United States. The transfer of GM corn byproducts from agricultural fields to nearby streams after harvest is significant and occurs well into the post-harvest year. These corn leaves, stems, and cobs then become a detrital food source for organisms, such as shredders in the stream ecosystem. Considering that the nontarget effects of Bt corn have been observed in some terrestrial organisms, we assessed whether Bt toxins affect an important aquatic organism, juvenile F. rusticus crayfish. Juvenile crayfish were fed six distinct diet treatments: two varieties of Bt corn, two non-Bt controls of herbicide tolerant corn, and two controls: fish gelatin and river detritus. Juveniles were fed these diets while housed in flow-through artificial streams that received natural stream water from a local source. Specific growth rate and survivorship of the crayfish were measured throughout the study. Juveniles fed corn diets grew significantly less and had reduced survival compared with juveniles fed fish gelatin or river detritus diets. Furthermore, juveniles fed one Bt variety of corn (VT Triple Pro^®) exhibited significantly less growth than those fed one of the herbicide tolerant varieties (Roundup Ready 2^®). Our study shows that corn inputs to streams may be detrimental to the growth and survivorship of juvenile crayfish and that certain Bt varieties may exacerbate these negative effects. These effects on crayfish will have repercussions for the entire ecosystem, because crayfish are conduits of energy between many trophic levels.

Persistence of insecticidal Cry toxins in Bt rice residues under field conditions estimated by biological and immunological assays

One risk of growing Bacillus thuringiensis (Bt) crops is the potential nontarget effects which are likely related to the environmental behavior of crystal (Cry) toxins. Bt rice residues left in field after harvest constitute a main source of Cry toxins entering the environment. To our knowledge, very few studies have simultaneously evaluated the persistence of Cry toxins in Bt rice residues under field conditions using different methods. Here, we established a bioassay method with a target insect: the striped stem borer (SSB), Chilo suppressalis Walker. The reaction limit of the SSB to Cry toxins ranged from 5.4 to 12.7 ng g^-1 in artificial diet, indicating that the detection limit of the bioassay ranged from 54 to 127 ng g^-1 rice residues. A field decomposition experiment lasting for 210 d was conducted with the straw of two Bt rice lines transformed with either cry1Ab/1Ac or cry2A. Enzyme-linked immunosorbent assays (ELISAs) revealed that the Cry toxins in the Bt rice residues experienced rapid degradation to below 25% of the initial level in the first 42 d, and then decreased to below 100 ng g^-1 rice residues within 100 to 140 d. Flooded conditions accelerated the degradation in the beginning compared with buried conditions. The Cry toxins were still detectable by ELISA, although at levels below 10 ng g^-1 rice residues (<0.3% of the initial level) 210 d after harvest. However, the bioassay revealed that the SSB no longer had a significant reaction to Bt rice residues added into artificial diets 16 to 18 d after harvest under both conditions, which indicated that the level of bioactive Cry toxins had declined to below the detection limit. Our results suggest that ELISA overestimate the persistence of Cry toxins and that the potential risks mediated by Cry toxins may be much smaller than originally expected.

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

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 (vf = 0.059 ± 0.009 mm s-1) was comparable to previously reported uptake of labile dissolved organic carbon (DOC; mean vf = 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.

Impact of genetically modified organisms on aquatic environments: Review of available data for the risk assessment

The aquatic environment is strongly connected to the surrounding agricultural landscapes, which regularly serve as sources of stressors such as agrochemicals. Genetically modified crops, which are cultivated on a large scale in many countries, may also act as stressors. Despite the commercial use of genetically modified organisms (GMOs) for over 20years, their impact on the aquatic environment came into focus only 10years ago. We present the status quo of the available scientific data in order to provide an input for informed aquatic risk assessment of GMOs. We could identify only 39 publications, including 84 studies, dealing with GMOs in the aquatic environment, and our analysis shows substantial knowledge gaps. The available information is restricted to a small number of crop plants, traits, events, and test organisms. The analysis of effect studies reveals that only a narrow range of organisms has been tested and that studies on combinatorial actions of stressors are virtually absent. The analysis of fate studies shows that many aspects, such as the fate of leached toxins, degradation of plant material, and distribution of crop residues in the aquatic habitat, are insufficiently investigated. Together with these research needs, we identify standardization of test methods as an issue of high priority, both for research and risk assessment needed for GMO regulation.