Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field

Impact of dual Bt-transgenic maize (2A7) on soil microbial communities and enzyme activities: A comparative study with control variety Z58

The impacts of transgenic crops on soil microbiology and fertility are critical in determining their biosafety. While transgenic crops can alter soil microbes, their effects are often context-dependent; therefore, the ecological importance of these changes remains a topic of ongoing research. Using high-throughput sequencing, we investigated the effects of Bacillus thuringiensis (Bt) maize expressing the mcry1Ab and mcry2Ab genes (2A7) on soil nutrient dynamics, as well as the diversity and function of soil microbial communities, including bacteria and fungi, within different soil compartments. Our findings revealed a plant-shaped rhizosphere (RS) microbial community as a result of the selective recruitment of microorganisms from the surrounding environment. The transgene insertion had a significant impact on the RS niche, and several species eventually became associated with Z58 and 2A7 plants. For example, Neocosmospora rubicola fungal and Pantoea dispersa bacterial microorganisms were significantly decreased in the dual Bt-transgenic 2A7 rhizosphere but enriched in the Z58 rhizospheres. The activity of soil enzymes such as urease, invertase, and alkaline phosphatase was boosted by Bt-transgenic 2A7. LefSe analysis identified significant bacterial and fungal biomarker species that were responsible for the differential effects of Bt-transgenic 2A7 and control Z58 within rhizosphere soils. Mantel analysis further demonstrated that the root exudates of 2A7 altered nutrient-acquisition enzymes by influencing biomarker taxa. PICRUSt2 functional characterization revealed a significantly higher abundance of the phosphate-starvation-inducible protein in control Z58 than in Bt-transgenic 2A7. Furthermore, taxonomy, alpha (Shannon diversity), and beta diversity analyses all revealed niche-driven microbial profile differentiation. Niche partitioning also had a significant impact on N- and P-related COGs as well. Our findings suggests that Bt-transgenic 2A7 modulates rhizosphere microbial communities by affecting biomarker taxa and soil enzyme activity. These findings will promote sustainable agriculture practices by advancing our knowledge of the ecological effects of Bt crops on soil microbial communities.

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.

Biochemical analyses demonstrate that Bt maize has no adverse effects on Eisenia fetida

The potential effects of Bt (Bacillus thuringiensis) maize on non-target organisms should be evaluated before such maize is commercially planted. Earthworms play an indispensable role in the soil ecosystem; act as important bio-indicators of soil quality and environmental pollution. Therefore, earthworms are often used as the object to evaluate the non-target effect of Bt maize. To accelerate the commercialization of transgenic maize in China, a 90-day Eisenia fetida feeding experiment was conducted to evaluate the potential effects of Bt maize line, BT799—which was developed by China Agricultural University and contains the Cry1Ac gene—and its non-Bt conventional isoline—Zheng 58—on E. fetida. Our results showed that the Bt maize line had no significant effects on the growth, reproduction, or enzymatic activities of these earthworms. In summary, Bt maize had no toxic effects on E. fetida.

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.

Differential impact of Bt-transgenic rice plantings on bacterial community in three niches over consecutive years

Transgenic-Bacillus thuringiensis (Bt) crops express insecticidal proteins, which can accumulate in plants and soil where they may influence microbial populations. The impact of Bt crops on bacterial communities has only been assessed under short-term, and results have been contradictory. Here, we analyzed the bacterial communities in three niches, rhizosphere soil (RS), root endosphere (RE) and leaf endosphere (LE), of three Bt rice and their non-Bt parental lines for three consecutive years by high-throughput sequencing. In principal coordinate analysis (PCoA) and PERMANOVA (Adonis) analysis, operational taxonomic units (OTUs) were clustered primarily by niche type and differed significantly in the RE and LE but not in the RS between each of three Bt lines compared with the non-Bt rice line, and not in each respective niche among the three Bt rice lines. The bacterial communities in the RS of different rice lines over the 3 years were clustered mainly by year rather than by lines. The differential bacterial taxa among the lines did not overlap between years, presumably because Cry proteins are rapidly degraded in the soil. A network analysis of RS bacterial communities showed that the network complexity and density for the three Bt rice lines did not decrease compared with those for the non-Bt line. In conclusion, our results demonstrated that bacterial communities differed significantly in RE and LE between Bt and non-Bt rice lines, but the differences were mild and transient, and had no adverse impact on RS over the 3 years. This study provides favorable evidence in support of the commercialization of Bt rice.

Evaluation of the effect of transgenic Bt cotton on snails Bradybaena (Acusta) ravida and Bradybaena similaris (Ferussac)

The impact of transgenic crops on non-target organisms is a key aspect of environmental safety assessment to transgenic crops. In the present study, we fed two snail species, Bradybaena (Acusta) ravida (B. ravida) and Bradybaena similaris (Ferussac)(B. similaris), with the leaves of transgenic Bt cotton Zhong 30 (Z30) and control cotton, its parent line zhong 16 (Z16), to assess the environmental safety of Bt cotton to common non-target organisms in the field. Survival, body weight, shell diameter, helix number, reproduction rate, superoxide dismutase (SOD) activity and Bt protein concentration in snails were monitored in 15 days and 180 days experiments. We also monitored the population dynamics of B. ravida and B. similaris in Z30 and Z16 cotton fields for two successive years. Compared to the snails fed on the control cotton Z16, there was no significant difference in survival, growth, reproduction, and SOD activity on Bt cotton Z30. Bt protein concentrations were significantly between different treatments, and Bt protein residues were only detected in the feces of the Z30 treatment. According to the field data, the number of B. ravida and B. similaris fluctuated considerably across seasons over the entire cotton-growing season; however, there were no significant differences between the Bt and control cotton fields at similar time. As the results showed, in our experiments, Bt cotton Z30 had no adverse effects on the two snail species, both in the laboratory and in the fields.

Degradation of transgenic Bacillus thuringiensis proteins in corn tissue in response to post-harvest management practices

Knowledge of the persistence of Cry proteins in transgenic corn residue after harvest is necessary to assess the ecological risk to nontarget organisms. The amount of protein remaining in crop residue declines over time by a combination of microbial decomposition and leaching, both influenced by temperature, precipitation, and the amount of residue-soil contact. Here, we investigated how long biologically active Cry proteins persist in SmartStax corn residue expressing Cry1A.105, Cry1F, Cry2Ab2, Cry3Bb1, and Cry34/35Ab1, when subjected to four post-harvest practices (chisel plow tillage, flail mowing, cover crop planting, and undisturbed residue). Protein activity in residue samples collected up to 25 weeks after harvest was measured by Ostrinia nubilalis feeding bioassays and cross validated with detection frequencies determined by ELISA. All corn residue remained above ground in the flail-mowed and undisturbed treatments, while the cover crop and chisel plow treatments left 88.3 and 39.6% of the residue remaining above ground, respectively. Cry proteins retained biological activity for as long as 24 weeks after harvest when residue was left above ground with less soil contact, typical of no-till corn systems. ELISA detections were positively correlated with results of the feeding bioassays, which revealed the presence of active proteins beyond the point of ELISA detection.

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.

Use of Taxonomic and Trait-Based Approaches to Evaluate the Effect of Bt maize Expressing Cry1Ie Protein on Non-Target Collembola: A Case Study in Northeast China

Simple Summary

Bt crops have been planted globally since the first commercial Bt maize was cultivated in the United States in 1996. Bt protein from Bt crops can be released to the soil and may potentially affect the non-target soil fauna. Collembola are one of the three most ubiquitous and abundant soil fauna, they have been widely used as indicators of environmental pollution, IE09S034 is a new cry1Ie maize breed independently developed by China, and Northeast China is the most important location for maize production in China. Therefore, this study aimed to clarify whether non-target soil Collembola were influenced by the cultivation of cry1Ie maize in Northeast China. Our results showed that maize variety had no significant effects on collembolan abundance, diversity, and morphological trait, indicating that two years cultivation of cry1Ie maize does not have a bad influence on Collembola in Northeast China.

Abstract

To evaluate the effect of Bt maize expressing Cry1Ie protein on non-target soil Collembola, a two-year field study was conducted in Northeast China. Bt maize line IE09S034 and its near isoline Zong 31 were selected as experimental crops; we investigated the collembolan community using both taxonomic and trait-based approaches, and elucidated the relationship between environmental variables and the collembolan community using redundancy analysis (RDA).The ANOVA results showed that maize variety neither had significant effect on the parameters based on taxonomic approach (abundance, species richness, Shannon–Wiener index, Pielou’s evenness index), nor on the parameters based on trait-based approach (ocelli number, body length, pigmentation level, and furcula development) in either year. The results of RDA also showed that maize variety did not affect collembolan community significantly. These results suggest that two years cultivation of cry1Ie maize does not affect collembolan community in Northeast China.

Absorption, translocation, and effects of Bt Cry1Ac peptides from transgenic cotton to the intercrops and soil functional bacteria

Insecticidal proteins encoded by the truncated genes from Bacillus thuringiensis (Bt) in transgenic crops are released into soil mainly through root exudate and crop residues. In the present study, Bt Cry1Ac protein was hydrolyzed by pronase that was secreted by the soil bacterium Streptomyces griseus. Six peptides were identified as the products of enzymatic hydrolysis by nano liquid chromatography tandem mass spectrometry (LC-MS/MS). One of the six peptides was labeled with radioactive isotope iodine-125 and then purified. The ¹²⁵I-peptide solution was irrigated to the rhizosphere soil of watermelon seedlings (Citrullus lanatus L.) and wheat seedlings (Triticum aestivum L.), which the two crops usually intercrop with cotton in China. Detection of radioactivity in both plant tissues within one hour proved adsorption, uptake and translocation of the peptide into watermelon and wheat seedlings. Three of the identified peptides were sprayed onto the seedling leaves of watermelon, wheat and maize (Zea mays L.) in the field or the growth chamber. No significant effects on plant growth were observed. These peptides also did not affect growth of organic phosphate-dissolving, nitrogen-fixing, and potassium-dissolving bacteria in the culture. This study provides a new view of GMO risk assessment methodology.

Dissipation of DvSnf7 RNA from Late-Season Maize Tissue in Aquatic Microcosms

The commercialization of RNA-based agricultural products requires robust ecological risk assessments. Ecological risk is operationally defined as a function of exposure and adverse effects. Information on the environmental fate of RNA-based plant-incorporated protectants is essential to define routes and duration of exposure to potentially sensitive nontarget organisms. Providing these details in problem formulation helps focus the ecological risk assessment on the relevant species of concern. Postharvest plant residue is often considered to be the most significant route of exposure for genetically modified crops to adjacent aquatic environments. Previous studies have shown that DvSnf7 RNA from SmartStax PRO maize dissipates rapidly in both terrestrial and aquatic environments. Although these studies suggest that direct exposure to DvSnf7 RNA is likely to be low, little is known regarding the fate of DvSnf7 RNA produced in plants after entering an aquatic environment. This exposure scenario is relevant to detritivorous aquatic invertebrates that process conditioned maize tissues that enter aquatic environments. To assess potential exposure to shredders, dissipation of DvSnf7 RNA expressed maize tissue was evaluated following immersion in microcosms containing sediment and water. Concentrations of DvSnf7 RNA in the tissue were measured over a duration of 21 d. The DvSnf7 RNA dissipated rapidly from immersed maize tissue and was undetectable in the tissues after 3 d. Concentrations of DvSnf7 RNA found in tissue as well as calculated water column concentrations were below levels known to elicit effects in a highly sensitive surrogate species, supporting the conclusion of minimal risk to aquatic nontarget organisms. Environ Toxicol Chem 2020;39:1032-1040. © 2020 SETAC.

Effect of Bt toxin Cry1Ab on two freshwater caddisfly shredders - an attempt to establish dose-effect relationships through food-spiking

Genetically modified organisms (GMOs), which produce Bacillus thuringiensis (Bt) toxins, are widely used in agriculture in some parts of the world. Despite this, ecotoxicological methods, tailored to GMOs, are lacking to assess effects on aquatic environments. With the objective to investigate a food-related exposure pathway for aquatic shredders, we used a new food-spiking method while caddisfly larvae (Chaetopteryx spec., Sericostoma spec.) served as test species. Pure Cry1Ab toxins were spiked on black alder leaf discs and subsequently used in a feeding experiment. The toxin did not influence larval mortality compared to the control. The results, however, showed significant effects on larval lipid content (Chaetopteryx spec.) and development (Sericostoma spec.) at concentrations of 17.2 and 132.4 ng Cry1Ab/mg leaf, respectively. These changes are indicative for impacts on the fitness of the specimen and thus relevant in a risk assessment context. Ultimately, the food-spiking method allowed applying different Bt toxin concentrations leading to the establishment of dose-response relationships for various response variables. The use of long test durations and sublethal endpoints (consumption, lipid content, growth, larval instars) is, moreover, advisable when testing GMO effects.

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.

Biological influence of cry1Ab gene insertion on the endophytic bacteria community in transgenic rice

The commercial release of genetically modified (GMO) rice for insect control in China is a subject of debate. Although a series of studies have focused on the safety evaluation of the agroecosystem, the endophytes of transgenic rice are rarely considered. Here, the influence of endophyte populations and communities was investigated and compared for transgenic and nontransgenic rice. Population-level investigation suggested that cry1Ab gene insertion influenced to a varying degree the rice endophytes at the seedling stage, but a significant difference was only observed in leaves of Bt22 (Zhejiang22 transgenic rice) between the GMO and wild-type rice. Community-level analysis using the 16S rRNA gene showed that strains of the phyla Proteobacteria and Firmicutes were the predominant groups occurring in the three transgenic rice plants and their corresponding parents. By contrast, the endophytic communities of Minghui63 and Xiushui11 showed a weaker response to cry1Ab gene insertion than did Zhejiang22, and the community results were consistent with the population-level investigation. The populations and communities of rice endophytes were affected by the cry1Ab gene to a different extent in different rice varieties and plant tissues. The results of this study broaden our understanding of unexpected transgenic influences on nontarget organisms.

Effects of Cry1Ab-expressing Bt rice straw return on juvenile and adult Eisenia fetida

A 90 day experiment was conducted in the laboratory to investigate the potential effects of transgenic Cry1Ab-expressing rice (Bacillus thuringiensis (Bt) rice: T775 and its F1 hybrid) straw return on earthworm Eisenia fetida, compared to non-Bt rice (TYHZ) straw. Juvenile E. fetida could survive, grow up, mature and reproduce offspring well in a Bt rice treated test during the whole experiment. The significantly higher relative growth rate (RGR) was found in earthworms from Bt rice treatment than from non-Bt rice treatment on the 7th day. The period of sexual maturity for earthworms from Bt rice treatments was shortened significantly, compared to non-Bt rice treatments. Adult E. fetida survived with weight loss under Bt rice treatments. On the 7th and 15th day, earthworm RGR decreased and glutathione peroxidase (GSH-PX) activity increased under Bt rice straw treatments. Significantly fewer offspring were produced by earthworms from Bt rice than non-Bt rice treatments on the 60th and 75th day. Enzyme-linked immunosorbent assay (ELISA) determined a sharp decrease of Cry1Ab in straw mixed soil along with the experimental time, regardless of juvenile or adult earthworm treatments. Cry1Ab concentration in the earthworms from the juvenile group was significantly higher than those from the adult group. Bt rice straw return had significant effects on soil nutrients, especially on the content of total and available phosphorus. In view of two bioassays, Bt rice (T775 and its F1 hybrid) straw return presented different effects on E. fetida from the juvenile (no deleterious effect) and adult (a little negative effect) groups, that were not directly related to Cry1Ab presence and nutrient differences among the three rice variety treatments.

Use of Taxonomic and Trait-Based Approaches to Evaluate the Effects of Transgenic Cry1Ac Corn on the Community Characteristics of Soil Collembola

Nontarget soil fauna in fields planted with transgenic Bt crops may be influenced by the Bt protein following crop establishment. Here, we investigated the effects of transgenic Cry1Ac corn Bt-799 on soil Collembola using both taxonomic and trait-based approaches in an experimental field in northeast China from 2014 to 2015. The relationship between the collembolan community and environmental variables (including corn type) was investigated using redundancy analysis (RDA). In May 2015, we found that collembolan species richness, Shannon-Wiener's index, and all trait values examined in transgenic Cry1Ac corn (Event Bt-799, Bt corn) were lower than in its near isoline (Zheng 58, non-Bt corn). However, this significant influence did not persist in the subsequent corn growth period. For all other sampling periods over 2-yr study, all indices based on taxonomic (abundance, species richness, and Shannon-Wiener's index) and trait-based (number of ocelli, body size, pigmentation, furcula development, and antennae length) approaches in Bt corn were not significantly different from non-Bt corn. The results showed no significant difference between the two corn types in the repeated-measures analysis of variance (ANOVA). Moreover, redundancy analysis (RDA) showed that corn type only explained 1% of the variation in the collembolan community. These results suggested that Bt corn did not affect collembolan community characteristics in the short term.

Bacterial communities under long-term conventional and transgenic cotton farming systems using V3-V5 and V5-V9 of 16s rDNA

Understanding the community structure of soil microbes is required to evaluate the potential effects of genetically modified (GM) plants on ecological environments. Bacterial communities in soil planted with conventional cotton (CC) and transgenic cultivar (TC) in a natural ecosystem for three years were characterized by 454 pyrosequencing of the V3-V5 and V5-V9 regions of 16S rDNA from June to September 2013. V3-V5 and V5-V9 regions yielded a total of 12,848 and 10,541 OTUs, respectively. The V5-V9 amplicon was additionally used to detect phyla that were poorly sequenced by V3-V5 (such as Chlamydiae, Crenarchaeota and Archaea). Among the species detected by each primer pair, 46% of the species identified from V3-V5 and 60% of those identified from V5-V9 were detected by both primer pairs. Although distinct bacterial compositions existed between the two amplified regions, statistical analysis revealed no significant difference in the diversity indexes or phylogenetic patterns in TC versus compared to those in the CC control. Further, clustering analysis in both regions indicated that there was no unambiguous aggregation in TC compared to that in CC control. Of all 26 phyla detected by both regions, each region detected 2 distinct phyla exhibiting significant variations in abundance. The species unique to each treatment field accounted for less than 27% of all species and were rare taxa (abundance < 0.15%). However, a small fraction of diagnostic taxa with specific ecological functions differed significantly between TC and CC. These differences were not driven by any obvious environmental factors. The results established a comprehensive inventory of the bacterial communities associated with GM plants and indicated that transgenic cotton may not significantly affect soil microorganisms compared with conventional cotton over a three-year period. Furthermore, diagnostic taxa were provided for monitoring the perturbation in soil, but further verification in future studies is required.

Soil incubation studies with Cry1Ac protein indicate no adverse effect of Bt crops on soil microbial communities

Bt crops that are transgenic crops engineered to produce Bt toxins which occur naturally with Bacillus thuringiensis (Bt) have been widely planted and its environmental risk assessment has been heavily debated. The effects of Bt crops on soil microbial communities are possible through changing the quantity and quality of C inputs and potential toxic activity of Bt protein on soil organisms. To date, the direct effects of Bt protein on soil microorganisms is unclear. Here we added Cry1Ac, one of the most commonly used Bt protein in Bt crops, to the soil and monitored changes in soil bacterial, fungal and archaeal diversities and community structures using ribosomal DNA-fingerprinting method, as well as their population sizes by real-time PCR over a 100-day period. Despite the fact that variations were observed in the indices of evenness, diversity and population sizes of bacteria, fungi and archaea with different Cry1Ac addition rates up to 100ngg^-1 soil, the indices of soil microbial diversities and evennesses did not significantly shift with Cry1Ac protein addition, nor did population sizes change over time. The diversities of the dominant bacteria, fungi and archaea were not significantly changed, given Cry1Ac protein addition rates over a period of 100 days. These results suggested that Bt protein derived by cultivations of transgenic Bt crops is unlikely to cause transient or even persisting significant changes in soil microorganisms in field.

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

Plant-incorporated protectants (PIPs) are biopesticides expressed in genetically modified (GM) crops and are typically macromolecular in nature. First-generation insecticidal PIPs were Cry proteins expressed in GM crops containing transgenes from the soil bacterium Bacillus thuringiensis; next-generation double-stranded ribonucleic acid (dsRNA) PIPs have been recently approved. Like conventional synthetic pesticides, the use of either Cry protein or dsRNA PIPs results in their release to receiving environments. However, as opposed to conventional low molecular weight pesticides, the environmental fate of macromolecular PIPs remains less studied and is poorly understood. This Feature highlights the knowledge gaps and challenges that have emerged while investigating the environmental fate of Cry protein PIPs and suggests new avenues to advance the state of the research necessary for the ongoing environmental fate assessment of dsRNA PIPs.

The distinct properties of natural and GM cry insecticidal proteins

The Cry toxins are a family of crystal-forming proteins produced by the bacterium Bacillus thuringiensis. Their mode of action is thought to be to create pores that disrupt the gut epithelial membranes of juvenile insects. These pores allow pathogen entry into the hemocoel, thereby killing the insect. Genes encoding a spectrum of Cry toxins, including Cry mutants, Cry chimaeras and other Cry derivatives, are used commercially to enhance insect resistance in genetically modified (GM) crops. In most countries of the world, such GM crops are regulated and must be assessed for human and environmental safety. However, such risk assessments often do not test the GM crop or its tissues directly. Instead, assessments rely primarily on historical information from naturally occurring Cry proteins and on data collected on Cry proteins (called 'surrogates') purified from laboratory strains of bacteria engineered to express Cry protein. However, neither surrogates nor naturally occurring Cry proteins are identical to the proteins to which humans or other nontarget organisms are exposed by the production and consumption of GM plants. To-date there has been no systematic survey of these differences. This review fills this knowledge gap with respect to the most commonly grown GM Cry-containing crops approved for international use. Having described the specific differences between natural, surrogate and GM Cry proteins this review assesses these differences for their potential to undermine the reliability of risk assessments. Lastly, we make specific recommendations for improving risk assessments.

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

The insecticidal Cry1Ab protein expressed by transgenic (Bt) maize can enter adjacent water bodies via multiple pathways, but its fate in stream ecosystems is not as well studied as in terrestrial systems. In this study, we used a combination of field sampling and laboratory experiments to examine the occurrence, leaching, and degradation of soluble Cry1Ab protein derived from Bt maize in agricultural streams. We surveyed 11 agricultural streams in northwestern Indiana, USA, on 6 dates that encompassed the growing season, crop harvest, and snowmelt/spring flooding, and detected Cry1Ab protein in the water column and in flowing subsurface tile drains at concentrations of 3-60ng/L. In a series of laboratory experiments, submerged Bt maize leaves leached Cry1Ab into stream water with 1% of the protein remaining in leaves after 70d. Laboratory experiments suggested that dissolved Cry1Ab protein degraded rapidly in microcosms containing water-column microorganisms, and light did not enhance breakdown by stimulating assimilatory uptake of the protein by autotrophs. The common detection of Cry1Ab protein in streams sampled across an agricultural landscape, combined with laboratory studies showing rapid leaching and degradation, suggests that Cry1Ab may be pseudo-persistent at the watershed scale due to the multiple input pathways from the surrounding terrestrial environment.

No effect of Bt-transgenic rice litter on the meiobenthos community in field ditches

BACKGROUND

The non-target effect of Bacillus thuringiensis (Bt) toxins in aquatic ecosystems is crucial to improve the present assessment of Bt-transgenic plants, particularly where crops are cultivated near aquatic ecosystems. We conducted decomposition experiments during two growing seasons to determine the effects of Bt-transgenic rice litter with and without insecticide application on the meiobenthos communities in a field ditch.

RESULTS

The community composition of meiobenthos colonised on leaf litter was not significantly different between Bt and non-Bt rice. The abundance of meiobenthos colonising leaves differed between insecticide application and control, and this insecticide effect interacted with rice type. No Bt toxin was detected in field ditch water. Leaf decomposition and nutrient content were comparable for both Bt and non-Bt rice with or without insecticide application.

CONCLUSION

Bt-transgenic rice litter had no effect on the meiobenthos community composition in field ditches, but the chronic persistence of transgenic litter in nature needs to be taken into account at large scales in aquatic ecosystems. © 2016 Society of Chemical Industry.

Effects of Cry1Ab Bt maize straw return on bacterial community of earthworm Eisenia fetida

The eco-toxicological effects of Bacillus thuringiensis (Bt) maize on earthworm life-history traits were widely studied and the results were controversial, while their effects on earthworm bacterial community have been rarely studied. Here, effects of two hybrids of Bt maize [5422Bt1 (event Bt11) and 5422CBCL (MON810)] straw return on Eisenia fetida bacterial community were investigated by the terminal restriction fragment length polymorphism (T-RFLP) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) combing with DNA sequencing, compared to near-isogenic non-Bt maize (5422). Bt maize straw return had significant effects on soil nutrients, especially for available nitrogen (N). The significant differences were shown in soil bacterial community between Bt and non-Bt maize treatments on the 75^th and 90^th d, which was closely correlated with soil available N, P and K rather than Cry1Ab protein. There was no statistically significant difference in the bacterial community of earthworm gut contents between Bt and non-Bt maize treatments. The significant differences in the bacterial community of earthworm casts were found among three maize varieties treatments, which were closely correlated with Cry1Ab protein and N levels. The differentiated bacterial species in earthworm casts mainly belonged to Proteobacteria, including Brevundimonas, Caulobacter, Pseudomonas, Stenotrophomonas, Methylobacterium, Asticcacaulis and Achromobacter etc., which were associated with the mineralization, metabolic process and degradation of plants residues. Therefore, Bt maize straw return caused changes in the bacterial community of E. fetida casts, which was possibly caused by the direct (Cry1Ab protein) and non-expected effects (N levels) of Bt maize straw.

Establishment of a sandwich enzyme-linked immunosorbent assay for specific detection of Bacillus thuringiensis (Bt) Cry1Ab toxin utilizing a monoclonal antibody produced with a novel hapten designed with molecular model

Cry1Ab toxin is commonly expressed in genetically modified crops in order to control chewing pests. At present, the detection method with enzyme-linked immunosorbent assay (ELISA) based on monoclonal antibody cannot specifically detect Cry1Ab toxin for Cry1Ab's amino acid sequence and spatial structure are highly similar to Cry1Ac toxin. In this study, based on molecular design, a novel hapten polypeptide was synthesized and conjugated to keyhole limpet hemocyanin (KLH). Then, through animal immunization with this antigen, a monoclonal antibody named 2C12, showing high affinity to Cry1Ab and having no cross reaction with Cry1Ac, was produced. The equilibrium dissociation constant (K _D) value of Cry1Ab toxin with MAb 2C12 was 1.947 × 10^-8 M. Based on this specific monoclonal antibody, a sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was developed for the specific determination of Cry1Ab toxin and the LOD and LOQ values were determined as 0.47 ± 0.11 and 2.43 ± 0.19 ng mL^-1, respectively. The average recoveries of Cry1Ab from spiked rice leaf and rice flour samples ranged from 75 to 115%, with coefficient of variation (CV) less than 8.6% within the quantitation range (2.5-100 ng mL^-1), showing good accuracy for the quantitative detection of Cry1Ab toxin in agricultural samples. In conclusion, this study provides a new approach for the production of high specific antibody and the newly developed DAS-ELISA is a useful method for Cry1Ab monitoring in agriculture products. Graphical Abstract Establishment of a DAS-ELISA for the specific detecting of Bacillus thuringiensis (Bt) Cry1Ab toxin.

Antibodies as epidemiological markers of genetically modified crop exposure: detection of Cry1Ab-specific IgG

There has been an increasing concern with the safety of genetically modified (GM) crops. An important modification of GM crops is the expression of Bacillus thuringiensis (Bt) protein, Cry1Ab. Animal exposure to Cry1Ab indicates that the protein is safe, but that it is immunogenic. Whether Cry1Ab is a human immunogen and whether antibody response to this protein can serve as a marker of high exposure to GM crops is unknown. Here we develop an enzyme-linked immunosorbent assay to detect the presence of Cry1Ab-specific IgG in ~100 individuals living in each of three countries that have varied exposure to GM crops (Papua New Guinea (PNG), low exposure; Kenya, moderate exposure; and the USA, high exposure). Cry1Ab-specific IgG antibodies were detected in individuals living in each region (8%, the USA; 3%, PNG; and 2%, Kenya). Thus, individuals develop anti-Cry1Ab antibodies at a frequency that roughly correlates with the exposure to GM crops expressing this protein.

Effects of Bt-transgenic rice cultivation on planktonic communities in paddy fields and adjacent ditches

The non-target effects of transgenic plants are issues of concern; however, their impacts in cultivated agricultural fields and adjacent natural aquatic ecosystems are poorly understood. We conducted field experiments during two growing seasons to determine the effects of cultivating Bacillus thuringiensis (Bt)-transgenic rice on the phytoplankton and zooplankton communities in a paddy field and an adjacent ditch. Bt toxin was detected in soil but not in water. Water quality was not significantly different between non-Bt and Bt rice fields, but varied among up-, mid- and downstream locations in the ditch. Cultivation of Bt-transgenic rice had no effects on zooplankton communities. Phytoplankton abundance and biodiversity were not significantly different between transgenic and non-transgenic rice fields in 2013; however, phytoplankton were more abundant in the transgenic rice field than in the non-transgenic rice field in 2014. Water quality and rice type explained 65.9% and 12.8% of this difference in 2014, respectively. Phytoplankton and zooplankton were more abundant in mid- and downstream, than upstream, locations in the ditch, an effect that we attribute to water quality differences. Thus, the release of Bt toxins into field water during the cultivation of transgenic crops had no direct negative effects on plankton community composition, but indirect effects that alter environmental conditions should be taken into account during the processes of management planning and policymaking.

Transgenic Crops to Address Third World Hunger? A Critical Analysis

Industry and mainstream research and policy institutions often suggest that transgenic crop varieties can raise the productivity of poor third world farmers, feed the hungry, and reduce poverty. These claims are critically evaluated by examining global-hunger data, the constraints that affect the productivity of small farmers in the third world, and the factors that explain their poverty. No significant role is found for crop genetics in determining hunger, productivity, or poverty, casting doubt on the ability of new transgenic crop varieties produced by genetic engineering to address these problems. An examination of the special risks these varieties pose for poor farmers in the complex, diverse, and risk-prone environments that characterize peasant agriculture on a global scale suggests that transgenic crop varieties are likely to be more of hindrance than a help to the advancement of poor farmers.

Current trends in Bt crops and their fate on associated microbial community dynamics: a review

Cry protein expressing insect-resistant trait is mostly deployed to control major devastating pests and minimize reliance on the conventional pesticides. However, the ethical and environmental issues are the major constraints in their acceptance, and consequently, the cultivation of genetically modified (GM) crops has invited intense debate. Since root exudates of Bacillus thuringiensis (Bt) crops harbor the insecticidal protein, there is a growing concern about the release and accumulation of soil-adsorbed Cry proteins and their impact on non-target microorganisms and soil microbial processes. This review pertains to reports from the laboratory studies and field trials to assess the Bt toxin proteins in soil microbes and the processes determining the soil quality in conjunction with the existing hypothesis and molecular approaches to elucidate the risk posed by the GM crops. Ecological perturbations hinder the risk aspect of soil microbiota in response to GM crops. Therefore, extensive research based on in vivo and interpretation of results using high-throughput techniques such as NGS on risk assessment are imperative to evaluate the impact of Bt crops to resolve the controversy related to their commercialization. But more studies are needed on the risk associated with stacked traits. Such studies would strengthen our knowledge about the plant-microbe interactions.

A Review of Cry Protein Detection with Enzyme-Linked Immunosorbent Assays

The widespread use of Cry proteins in insecticide formulations and transgenic crops for insect control has led to an increased interest in the environmental fate of these proteins. Although several detection methods are available to monitor the fate of Cry proteins in the environment, enzyme-linked immunosorbent assays (ELISAs) have emerged as the preferred detection method, due to their cost-effectiveness, ease of use, and rapid results. Validation of ELISAs is necessary to ensure accurate measurements of Cry protein concentrations in the environment. Validation methodology has been extensively researched and published for the areas of sensitivity, specificity, accuracy, and precision; however, cross validation of ELISA results has been studied to a lesser extent. This review discusses the use of ELISAs for detection of Cry proteins in environmental samples and validation of ELISAs and introduces cross validation. The state of Cry protein environmental fate research is considered through a critical review of published literature to identify areas where the use of validation protocols can be improved.

Prioritizing stream types according to their potential risk to receive crop plant material--A GIS-based procedure to assist in the risk assessment of genetically modified crops and systemic insecticide residues

Crop plant residues may enter aquatic ecosystems via wind deposition or surface runoff. In the case of genetically modified crops or crops treated with systemic pesticides, these materials may contain insecticidal Bt toxins or pesticides that potentially affect aquatic life. However, the particular exposure pattern of aquatic ecosystems (i.e., via plant material) is not properly reflected in current risk assessment schemes, which primarily focus on waterborne toxicity and not on plant material as the route of uptake. To assist in risk assessment, the present study proposes a prioritization procedure of stream types based on the freshwater network and crop-specific cultivation data using maize in Germany as a model system. To identify stream types with a high probability of receiving crop materials, we developed a formalized, criteria-based and thus transparent procedure that considers the exposure-related parameters, ecological status--an estimate of the diversity and potential vulnerability of local communities towards anthropogenic stress--and availability of uncontaminated reference sections. By applying the procedure to maize, ten stream types out of 38 are expected to be the most relevant if the ecological effects from plant-incorporated pesticides need to be evaluated. This information is an important first step to identifying habitats within these stream types with a high probability of receiving crop plant material at a more local scale, including accumulation areas. Moreover, the prioritization procedure developed in the present study may support the selection of aquatic species for ecotoxicological testing based on their probability of occurrence in stream types having a higher chance of exposure. Finally, this procedure can be adapted to any geographical region or crop of interest and is, therefore, a valuable tool for a site-specific risk assessment of crop plants carrying systemic pesticides or novel proteins, such as insecticidal Bt toxins, expressed in genetically modified crops.

Persistence of detectable insecticidal proteins from Bacillus thuringiensis (Cry) and toxicity after adsorption on contrasting soils

Insecticidal Cry, or Bt, proteins are produced by the soil-endemic bacterium, Bacillus thuringiensis and some genetically modified crops. Their environmental fate depends on interactions with soil. Little is known about the toxicity of adsorbed proteins and the change in toxicity over time. We incubated Cry1Ac and Cry2A in contrasting soils subjected to different treatments to inhibit microbial activity. The toxin was chemically extracted and immunoassayed. Manduca sexta was the target insect for biotests. Extractable toxin decreased during incubation for up to four weeks. Toxicity of Cry1Ac was maintained in the adsorbed state, but lost after 2 weeks incubation at 25 °C. The decline in extractable protein and toxicity were much slower at 4 °C with no significant effect of soil sterilization. The major driving force for decline may be time-dependent fixation of adsorbed protein, leading to a decrease in the extraction yield in vitro, paralleled by decreasing solubilisation in the larval gut.

Effects of water management practices on residue decomposition and degradation of Cry1Ac protein from crop-wild Bt rice hybrids and parental lines during winter fallow season

Rice is the staple diet of over half of the world's population and Bacillus thuringiensis (Bt) rice expressing insecticidal Cry proteins is ready for deployment. An assessment of the potential impact of Bt rice on the soil ecosystem under varied field management practices is urgently required. We used litter bags to assess the residue (leaves, stems and roots) decomposition dynamics of two transgenic rice lines (Kefeng6 and Kefeng8) containing stacked genes from Bt and sck (a modified CpTI gene encoding a cowpea trypsin inhibitor) (Bt/CpTI), a non-transgenic rice near-isoline (Minghui86), wild rice (Oryza rufipogon) and crop-wild Bt rice hybrid under contrasting conditions (drainage or continuous flooding) in the field. No significant difference was detected in the remaining mass, total C and total N among cultivars under aerobic conditions, whereas significant differences in the remaining mass and total C were detected between Kefeng6 and Kefeng8 and Minghui86 under the flooded condition. A higher decomposition rate constant (km) was measured under the flooded condition compared with the aerobic condition for leaf residues, whereas the reverse was observed for root residues. The enzyme-linked immunosorbent assay (ELISA), which was used to monitor the changes in the Cry1Ac protein in Bt rice residues, indicated that (1) the degradation of the Cry1Ac protein under both conditions best fit first-order kinetics, and the predicted DT50 (50% degradation time) of the Cry1Ac protein ranged from 3.6 to 32.5 days; (2) the Cry1Ac protein in the residue degraded relatively faster under aerobic conditions; and (3) by the end of the study (~154 days), the protein was present at a low concentration in the remaining residues under both conditions. The degradation rate constant was negatively correlated with the initial carbon content and positively correlated with the initial Cry1Ac protein concentration, but it was only correlated with the mass decomposition rate constants under the flooded condition. No Cry1Ac protein was detected in the soils surrounding the buried residue. Our results did not reveal any evidence that the stacked genes (Bt/CpTI) or the presence of the Cry1Ac protein influenced the decomposition dynamics of the rice residues. Furthermore, our results suggested that field drainage after residue incorporation would promote Cry1Ac protein degradation.

Toxicological and biochemical analyses demonstrate no toxic effect of Cry1C and Cry2A to Folsomia candida

Collembolans are common soil arthropods that may be exposed to insecticidal proteins produced in genetically engineered (GE) plants by ingestion of crop residues or root exudates. In the present study, a dietary exposure assay was validated and used to assess the lethal and sublethal effects of two Bacillus thuringiensis (Bt) insecticidal proteins, Cry1C and Cry2A, on Folsomia candida. Using the insecticidal compounds potassium arsenate (PA), protease inhibitor (E-64), and Galanthus nivalis agglutinin (GNA) mixed into Baker's yeast, we show that the assay used can detect adverse effects on F. candida. Survival and development were significantly reduced when F. candida was fed a diet containing PA, E-64, and GNA at 9, 75, and 100 μg/g diet, respectively, but not when fed a diet containing 300 μg/g Cry1C or 600 μg/g Cry2A. The activities of test antioxidant-, detoxification-, and digestion-related enzymes in F. candida were unaltered by a diet containing 300 μg/g Cry1C or 600 μg/g Cry2A, but were significantly increased by a diet containing 75 μg/g E-64. The results confirm that Cry1C and Cry2A are not toxic to F. candida at concentrations that are much higher than those encountered under field conditions.

Multilevel assessment of Cry1Ab Bt-maize straw return affecting the earthworm Eisenia fetida

Non-target effects of two varieties of Bacillus thuringiensis (Bt)-maize straw (5422Bt1 [event Bt11] and 5422CBCL [MON810]) return on the Eisenia fetida were investigated by using multilevel assessments, compared to near-isogenic non-Bt-maize (5422). 5422Bt1 straw return had no deleterious effects on adult earthworms and had significantly positive effects on juveniles over three generations. Negative, no, and positive effects on adults treated with 5422CBCL straw were observed in the 1st, 2nd and 3rd generation, respectively. Negative and positive effects were observed on juveniles produced from the 1st- and 2nd-generation adults treated with 5422CBCL straw, respectively. Glutathione peroxidase activity of earthworms from Bt-maize treatments was significantly higher than that of control on the 90th d. Translationally controlled tumour protein (TCTP) and superoxide dismutase (SOD) genes were down-regulated, while annetocin (ANN) expression was up-regulated in 5422Bt1 treatments. TCTP and SOD genes were up-regulated, while ANN and heat shock protein 70 were down-regulated in E. fetida from 5422CBCL treatments. Enzyme-linked immunosorbent assay revealed that Cry1Ab released from 5422Bt1 and 5422CBCL straw degraded rapidly on the 15th and 30th d and had a slow decline in the rest testing time. Cry1Ab concentrations in the soil, casts and guts of earthworm significantly decreased over the course of the experiment. This study was the first to evaluate generational effects of Bt-maize straw return on earthworms under laboratory conditions. The responses of enzymes activity and genes expression may contribute to better understand above different effects of Bt-maize straw return on earthworms from the 1st generation.

Aquatic degradation of Cry1Ab protein and decomposition dynamics of transgenic corn leaves under controlled conditions

The increasing cultivation of genetically modified corn plants (Zea mays) during the last decades is suggested as a potential risk to the environment. One of these genetically modified variety expressed the insecticidal Cry1Ab protein originating from Bacillus thuringiensis (Bt), resulting in resistance against Ostrinia nubilalis, the European corn borer. Transgenic litter material is extensively studied regarding the decomposition in soils. However, only a few field studies analyzed the fate of the Cry1Ab protein and the impact of green and senescent leaf litter from corn on the decomposition rate and related ecosystem functions in aquatic environments. Consequently, a microbial litter decomposition experiment was conducted under controlled semi-natural conditions in batch culture using two maize varieties: one variety with Cry1Ab and another one with the appertaining Iso-line as control treatment. The results showed no significant differences between the treatment with Cry1Ab and the Iso-line regarding loss of total mass in dry weight of 43% for Iso-line and 45% for Bt-corn litter, lignin content increased to 137.5% (Iso-line) and 115.7% (Bt-corn), and phenol loss decreased by 53.6% (Iso-line), 62.2% (Bt-corn) during three weeks of the experiment. At the end of the experiment Cry1Ab protein was still detected with 6% of the initial concentration. A slightly but significant lower cellulose content was found for the Cry1Ab treatment compared to the Iso-line litter at the end of the experiment. The significant higher total protein (25%) and nitrogen (25%) content in Bt corn, most likely due to the additionally expression of the transgenic protein, may increase the microbial cellulose degradation and decrease microbial lignin degradation. In conclusion a relevant year by year input of protein and therefore nitrogen rich Bt corn litter into aquatic environments may affect the balanced nutrient turnover in aquatic ecosystems.

Impact of water content and temperature on the degradation of Cry1Ac protein in leaves and buds of Bt cotton in the soil

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.

Validation of an extraction method for Cry1Ab protein from soil

Corn expressing insecticidal proteins derived from Bacillus thuringiensis (Bt corn) has increased in usage in the United States from 8% of total corn acreage in 1996 to 67% in 2012. Because of this increase, it is important to be able to monitor the fate and transport of the insecticidal Bt proteins to evaluate environmental exposure and effects. Accurate and validated methods are needed to quantify these proteins in environmental matrices. A method to extract Bt Cry1Ab proteins from 3 soil types using a 10× phosphate-buffered saline with Tween buffer and a commercially available enzyme-linked immunosorbent assay (ELISA) was validated through a series of 6 tests. The validation process for Cry1Ab extractions in soil has not yet been reported in the scientific literature. The extraction buffer and each soil matrix were tested and validated for the ELISA. Extraction efficiencies were 41%, 74%, and 89% for the 3 soil types and were significantly correlated with the organic matter content of the soil. Despite low recoveries, consistent results with low coefficients of variation allowed for accurate measurements. Through validating this method with 3 different soils, a sensitive, specific, precise, and accurate quantification of Bt Cry1Ab was developed. The validation process can be expanded and implemented in other environmental matrices, adding consistency to data across a wide range of samples.

Effects of insecticidal crystal proteins (Cry proteins) produced by genetically modified maize (Bt maize) on the nematode Caenorhabditis elegans

The genetically modified maize MON89034 × MON88017 expresses different crystal (Cry) proteins with pesticidal activity against the European corn borer (Cry1.105; Cry2Ab2) and the Western corn root worm (Cry3Bb1). Non-target organisms, such as soil nematodes, might be exposed to the Cry proteins that enter the soil in course of crop growing. Therefore, the risk of those proteins for nematodes was assessed by testing their toxic effects on Caenorhabditis elegans. All three insecticidal Cry proteins showed dose-dependent inhibitory effects on C. elegans reproduction (EC50: 0.12-0.38 μmol L(-1)), however, at concentrations that were far above the expected soil concentrations. Moreover, a reduced toxicity was observed when Cry proteins were added jointly. A C. elegans mutant strain deficient for receptors for the nematicidal Cry5B was also resistant against Cry1.105 and Cry2Ab2, suggesting that these Cry proteins bound to the same or similar receptors as nematicidal Cry proteins and thereby affect the reproduction of C. elegans.

Changes in Actinomycetes community structure under the influence of Bt transgenic brinjal crop in a tropical agroecosystem

BACKGROUND

The global area under brinjal cultivation is expected to be 1.85 million hectare with total fruit production about 32 million metric tons (MTs). Brinjal cultivars are susceptible to a variety of stresses that significantly limit productivity. The most important biotic stress is caused by the Brinjal fruit and shoot Borer (FSB) forcing farmers to deploy high doses of insecticides; a matter of serious health concern. Therefore, to control the adverse effect of insecticides on the environment including the soil, transgenic technology has emerged as the effective alternative. However, the reports, regarding the nature of interaction of transgenic crops with the native microbial community are inconsistent. The effect of a Bt transgenic brinjal expressing the bio-insecticidal protein (Cry1Ac) on the rhizospheric community of actinomycetes has been assessed and compared with its non-transgenic counterpart.

RESULTS

Significant variation in the organic carbon observed between the crops (non-Bt and Bt brinjal) may be due to changes in root exudates quality and composition mediated by genetic attributes of Bt transgenic brinjal. Real time quantitative PCR indicated significant differences in the actinomycetes- specific 16S rRNA gene copy numbers between the non-Bt (5.62-27.86) × 1011 g-1 dws and Bt brinjal planted soil (5.62-24.04) × 1011 g-1 dws. Phylogenetic analysis indicated 14 and 11, actinomycetes related groups in soil with non-Bt and Bt brinjal crop, respectively. Micrococaceaea and Nocardiodaceae were the dominant groups in pre-vegetation, branching, flowering, maturation and post-harvest stage. However, Promicromonosporaceae, Streptosporangiaceae, Mycobacteriaceae, Geodermatophilaceae, Frankiaceae, Kineosporaceae, Actisymmetaceae and Streptomycetaceae were exclusively detected in a few stages in non-Bt brinjal rhizosphere soil while Nakamurellaceae, Corynebactericeae, Thermomonosporaceae and Pseudonocardiaceae in Bt brinjal counterpart.

CONCLUSION

Field trails envisage that cultivation of Bt transgenic brinjal had negative effect on organic carbon which might be attributed to genetic modifications in the plant. Changes in the organic carbon also affect the actinomycetes population size and diversity associated with rhizospheric soils of both the crops. Further long-term study is required by taking account the natural cultivar apart from the Bt brinjal and its near-isogenic non-Bt brinjal with particular reference to the effects induced by the Bt transgenic brinjal across different plant growth stages.

Effects of transgenic Bt rice on growth, reproduction, and superoxide dismutase activity of Folsomia candida (Collembola: Isotomidae) in laboratory studies

Transgenic rice expressing Bacillus thuringiensis (Bt) CrylAb protein is expected to be commercialized in China in the near future. The use of Bt rice for controlling insect pests sparks intensive debates regarding its biosafety. Folsomia candida is an euedaphic species and is often used as a "standard" test organism in assessing effects of environmental pollutants on soil organisms. In this study, growth, development, reproduction, and superoxide dismutase activity (SOD) of F. candida were investigated in the laboratory for populations reared on leaf tissue or leaf-soil mixtures of two CrylAb rice lines and a non-Bt rice isoline. Two independent tests were performed: 1) a 35-d test using petri dishes containing yeast diet (positive control) or fresh rice leaf tissue, and 2) a 28-d test in soil-litter microcosms containing yeast or a mixture of soil and rice leaf tissue. Biological parameters measured in both tests were number of progeny production, population growth rate, and SOD activity. For the petri dish test, data measured also included insect body length and number of exuviation. There were no significant differences between the populations reared on Bt and non-Bt rice leaf tissue in all measured parameters in both tests and for both Bt rice lines, suggesting no significant effects of the CrylAb protein in Bt rice on F. candida in the laboratory studies. Results of this study should add additional biosafety proofs for use of Bt rice to manage rice pests in China.

The presence of Bacillus thuringiensis (Bt) protein in earthworms Eisenia fetida has no deleterious effects on their growth and reproduction

Earthworms Eisenia fetida, bred in substances with stover of two genetically-engineered Bacillus thuringiensis (Bt) corns (5422Bt1 (Event Bt11) and 5422CBCL (MON810)) expressing Cry1Ab and their near-isogenic non-Bt corn (5422), were used to investigate the non-target effects of Bt corn on soil-dwelling organisms. Cry1Ab concentrations in substances, casts and guts of E. fetida were also investigated by Enzyme-linked immunosorbent assay (ELISA). More than 90% individuals of E. fetida survived over a period of 30 d, irrespective of whether they received Bt corn or non-Bt corn. Compared to 5422 treatments, significantly higher relative growth rate and more number of new offspring and cocoons of E. fetida were found in 5422Bt1 and 5422CBCL treatments. These results were unlikely to be directly caused by Cry1Ab released from Bt corns but rather by differences in other factors of plants such as plant components (soluble sugar, total organic carbon, total protein and available phosphorus of Bt corns were more than 5422). ELISA results indicated immunoreactive Cry1Ab was detectable in substances, and the casts, guts of E. fetida from Bt corns treatments, of which the highest levels were detected in substances under the corresponding experimental conditions. With the increase of treated time, a strong decline was observed in Cry1Ab from substances and casts of E. fetida, whereas Cry1Ab in guts of E. fetida from 5422Bt1 treatments gradually increased and that from 5422CBCL treatments increased between 14 and 30 d. Therefore, the presence of Cry1Ab in E. fetida had no deleterious effects on their growth and reproduction.

Assessing the risk posed to free-living soil nematodes by a genetically modified maize expressing the insecticidal Cry3Bb1 protein

Before pest-resistant genetically modified maize can be grown commercially, the risks for soil-beneficial, non-target organisms must be determined. Here, a tiered approach was used to assess the risk to free-living soil nematodes posed by maize genetically modified to express the insecticidal Cry3Bb1 protein (event Mon88017), which confers resistance towards western corn rootworm (Diabrotica virgifera; Coleoptera). The toxicity of purified Cry3Bb1 for the nematode Caenorhabditis elegans was determined using a bioassay and gene expression analysis. In addition, a soil toxicity test was used to assess the effects on C. elegans of rhizosphere soil obtained from plots of an experimental field grown with Mon88017, the near-isogenic cultivar, or either of two conventional cultivars. Finally, the indigenous nematode communities from the experimental field site with Mon88017 and from the control cultivars were analyzed. The results showed a dose-dependent inhibitory effect of Cry3Bb1 on the growth and reproduction of C. elegans, with EC50 values of 22.3 mg l⁻¹ and 7.9 mg l⁻¹, respectively. Moreover, Cry-protein-specific defense genes were found to be up-regulated in the presence of either Cry1Ab or Cry3Bb1. However, C. elegans was not affected by rhizosphere soils from Mon88017 compared to the control plots, due to the very low Cry3Bb1 concentrations, as indicated by quantitative analyses (< 1 ng g⁻¹ soil). Nematode abundance and diversity were essentially the same between the various maize cultivars. At the last sampling date, nematode genus composition in Bt-maize plots differed significantly from that in two of the three non-Bt cultivars, including the near-isogenic maize, but the shift in genus composition did not influence the composition of functional guilds within the nematode communities. In conclusion, the risk to free-living soil nematodes posed by Mon88017 cultivation can be regarded as low, as long as Cry3Bb1 concentrations in soil remain four orders of magnitude below the toxicity threshold.

Effects of Consumption of Bt-maize (MON 810) on the Collembolan Folsomia candida, Over Multiple Generations: A Laboratory Study

The effect of long-term feeding on Bt-maize by collembolans in the laboratory is virtually unestablished. That is why the aim of the present study was to test whether the reproduction, fecal pellet production or food preference of the collembolan F. candida is affected when fed on Bt-maize for several consecutive generations. The collembolans were fed with Bt-maize for 0, 6, 16 and 22 months and the number of eggs and fecal pellets were determined. The experiment was repeated seven months later with the same populations. Food preference tests were additionally performed. Significant differences were found in food consumption, egg production and food preference between populations in some cases, but no time-response effect was observed. In conclusion, several generations feeding of F. candida on Cry1Ab toxin containing Bt-maize seems not to be harmful to this collembolan species.

Responses of stream macroinvertebrates to Bt maize leaf detritus

In the midwestern United States, maize detritus enters streams draining agricultural land. Genetically modified Bt maize is commonly planted along streams and can possibly affect benthic macroinvertebrates, specifically members of the order Trichoptera, which are closely related to target species of some Bt toxins and are important detritivores in streams. The significance of inputs of Bt maize to aquatic systems has only recently been recognized, and assessments of potential nontarget impacts on aquatic organisms are lacking. We conducted laboratory feeding trials and found that the leaf-shredding trichopteran, Lepidostoma liba, grew significantly slower when fed Bt maize compared to non-Bt maize, while other invertebrate taxa that we examined showed no negative effects. We also used field studies to assess the influence of Bt maize detritus on benthic macroinvertebrate abundance, diversity, biomass, and functional structure in situ in 12 streams adjacent to Bt maize or non-Bt maize fields. We found no significant differences in total abundance or biomass between Bt and non-Bt streams, and trichopterans comprised only a small percentage of invertebrate biomass at all sites (0-15%). Shannon diversity did not differ among Bt and non-Bt streams and was always low (H' range = 0.9-1.9). Highly tolerant taxa, such as oligochaetes and chironomids, were dominant in both Bt and non-Bt streams, and macroinvertebrate community composition was relatively constant across seasons. We used litterbags to examine macroinvertebrate colonization of Bt and non-Bt maize detritus and found no significant differences among litter or stream types. Our in situ findings did not support our laboratory results; this is likely because the streams we studied in this region are highly degraded and subject to multiple, persistent anthropogenic stressors (e.g., channelization, altered flow, nutrient and pesticide inputs). Invertebrate communities in these streams are a product of these degraded conditions, and thus the impact of a single stressor, such as Bt toxins, may not be readily discernable. Our results add to growing evidence that Bt toxins can have sublethal effects on nontarget aquatic taxa, but this evidence should be considered in the context of other anthropogenic impacts and alternative methods of pest control influencing streams draining agricultural regions.