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

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.

Identification and Characterization of HD1, a Novel Ofloxacin-Degrading Bacillus Strain

In recent years, an increasing number of lakes and soils around the world have been polluted by antibiotics, seriously threatening the ecological balance and human health. Currently, there is a lack of understanding of the biodegradation mechanism of typical antibiotics by microorganisms. In this study HD1, a novel Bacillus sp. strain called capable of effectively degrading ofloxacin (OFL), a typical antibiotic with a high detection rate in the environment, was isolated from soil contaminated by OFL. The results of single-factor experiments showed that the optimal conditions for OFL degradation included 30°C, pH 7.0, and 10 g L^–1 NaCl. After 7 days of incubation under aerobic conditions, the degradation efficiency of OFL (5 mg L^–1) was about 66.2%. Five degradation products were detected by LC-MS analysis, and it was deduced that the possible degradation pathways of OFL included the oxidation of the piperazine ring, demethylation, hydroxylation, and methoxy cleavage. Metabolomics analysis indicated that key pathways with the highest difference with HD1 metabolites included the phenylalanine, arginine, and proline metabolism pathways. By regulating energy, amino acid metabolism, and carbohydrate metabolism, HD1 could alleviate OFL stress to degrade better. This study explored the degradation mechanism of OFL by HD1 and provides a theoretical basis and technical support for the remediation of OFL-contaminated environments by functional microorganisms.

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.

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.

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.

Annual post-market environmental monitoring (PMEM) report on the cultivation of genetically modified maize MON 810 in 2015 from Monsanto Europe S.A

Following a request from the European Commission, the Panel on Genetically Modified Organisms of the European Food Safety Authority (GMO Panel) assessed the annual post-market environmental monitoring (PMEM) report for the 2015 growing season of the Cry1Ab-expressing maize event MON 810 provided by Monsanto Europe S.A. The GMO Panel concludes that the insect resistance monitoring data submitted to EFSA do not indicate a decrease in susceptibility of field Iberian populations of corn borers to the Cry1Ab protein during the 2015 season. However, since the methodology for insect resistance monitoring remained unchanged compared to previous PMEM reports, the GMO Panel reiterates its previous recommendations on resistance monitoring to provide sufficient detection sensitivity. Although the farmer alert system to report complaints about product performance could complement the information obtained from the laboratory bioassays, the GMO Panel is currently not in a position to appraise its usefulness, and therefore encourages the consent holder to provide more information on this complementary resistance monitoring tool. The data on general surveillance (GS) do not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. The GMO Panel reiterates its previous recommendations on the analysis of farmer questionnaires, and advises the consent holder to provide more detailed information on the conducting and reporting of the literature search in future annual PMEM reports. Moreover, the GMO Panel encourages relevant parties to continue developing a methodological framework to use existing networks in the broader context of environmental monitoring. The GMO Panel concludes that the case-specific monitoring (CSM) and GS activities of maize MON 810 as carried out by the consent holder do not provide evidence that would invalidate previous GMO Panel evaluations on the safety of maize MON 810.

Interactions between Bt crops and aquatic ecosystems: A review

The term Bt crops collectively refers to crops that have been genetically modified to include a gene (or genes) sourced from Bacillus thuringiensis (Bt) bacteria. These genes confer the ability to produce proteins toxic to certain insect pests. The interaction between Bt crops and adjacent aquatic ecosystems has received limited attention in research and risk assessment, despite the fact that some Bt crops have been in commercial use for 20 yr. Reports of effects on aquatic organisms such as Daphnia magna, Elliptio complanata, and Chironomus dilutus suggest that some aquatic species may be negatively affected, whereas other reports suggest that the decreased use of insecticides precipitated by Bt crops may benefit aquatic communities. The present study reviews the literature regarding entry routes and exposure pathways by which aquatic organisms may be exposed to Bt crop material, as well as feeding trials and field surveys that have investigated the effects of Bt-expressing plant material on such organisms. The present review also discusses how Bt crop development has moved past single-gene events, toward multigene stacked varieties that often contain herbicide resistance genes in addition to multiple Bt genes, and how their use (in conjunction with co-technology such as glyphosate/Roundup) may impact and interact with aquatic ecosystems. Lastly, suggestions for further research in this field are provided. Environ Toxicol Chem 2016;35:2891-2902. © 2016 SETAC.

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.