The effects of the presence of Bt-transgenic oilseed rape in wild mustard populations on the rhizosphere nematode and microbial communities

Evaluation of the Ecological Environment Affected by Cry1Ah1 in Poplar

Populus is a genus of globally significant plantation trees used widely in industrial and agricultural production. Poplars are easily damaged by Micromelalopha troglodyta and Hyphantria cunea, resulting in decreasing quality. Bt toxin-encoded by the Cry gene has been widely adopted in poplar breeding because of its strong insect resistance. There is still no comprehensive and sufficient information about the effects of Cry1Ah1-modified (CM) poplars on the ecological environment. Here, we sampled the rhizosphere soils of field-grown CM and non-transgenic (NT) poplars and applied 16S rRNA and internal transcribed spacer amplicon Illumina MiSeq sequencing to determine the bacterial community associated with the CM and NT poplars. Based on the high-throughput sequencing of samples, we found that the predominant taxa included Proteobacteria (about 40% of the total bacteria), Acidobacteria (about 20% of the total bacteria), and Actinobacteria (about 20% of the total bacteria) collected from the natural rhizosphere of NT and CM poplars. In addition, studies on the microbial diversity of poplar showed that Cry1Ah1 expression has no significant influence on rhizosphere soil alkaline nitrogen, but significantly affects soil phosphorus, soil microbial biomass nitrogen, and carbon. The results exhibited a similar bacterial community structure between CM varieties affected by the expression of Cry1Ah1 and non-transgenic poplars. In addition, Cry1Ah1 expression revealed no significant influence on the composition of rhizosphere microbiomes. These results broadly reflect the effect of the Bt toxin-encoded by Cry1Ah1 on the ecology and environment and provide a clear path for researchers to continue research in this field in the future.

Effects of Pest Management Practices on Soil Nematode Abundance, Diversity, Metabolic Footprint and Community Composition Under Paddy Rice Fields

The wide-scale adoption of transgenic crops has aroused public concern towards potential impacts to the ecological services of soil fauna, such as soil nematodes. However, few studies has examined whether the cultivation of transgenic rice would pose greater threats to soil nematode community and associated ecological functions than insecticides application. Moreover, what are determinants of soil nematode community in paddy fields remains unclear. During a 3-year field study, rhizosphere soil samples of transgenic-Bt rice, its counterpart non-Bt parental rice and not-Bt rice with insecticides application were taken at four times in the rice developmental cycle using a random block design with three replications for each treatment. We hypothesized that the effects of pest management practice on soil nematode abundance and metabolic footprint change with trophic group and sampling time. We also predicted there were significant differences in structure and composition of soil nematode community across the three treatments examined and sampling times. In agreement with our expectation, the effects of pest management practice on nematode abundance and metabolic footprints depend on trophic group and sampling time. However, pest management practice exerted no apparent effect on nematode diversity and community composition. Soil nutrient availability and C:N molar ratio are the primary regulating factor of soil nematode community in rice paddy fields. In conclusion, our findings implied that changes in abundance, diversity, metabolic footprints associated with the crop growth stage overweighed the application of Bt rice and insecticides. The cultivation of Bt rice Huahui-1 exerted no measurable adverse effect on soil nematode community in rhizosphere soil over 3 years of rice cropping.

Elevated CO2 not increased temperature has specific effects on soil nematode community either with planting of transgenic Bt rice or non-Bt rice

BACKGROUND

Transgenic Bt rice has not been approved for commercial cultivation because of the fierce public debate on food safety, biosafety regulation and ecological risk. Meanwhile, the concentration of CO2 and temperature in the atmosphere, as important environmental factors affecting the persistence of exogenous Bt protein, have increased. Elevated CO2, increased temperature, the planting of transgenic Bt rice and their interactions may further influence the structure and complexity of soil food web. However, the effects of transgenic Bt rice planting on soil organism remain largely unexplored before its commercial production especially under global climate change.

METHODS

Here, we assessed the influences of transgenic Bt rice (cv. HH with fused Cry1Ab/Cry1Ac in contrast to its parental line of non-Bt rice cv. MH63) on soil nematode communities under the conditions of elevated CO2 concentration and increased temperature for 2 years of 2016 and 2017 in open-top chambers located in Ningjin County, Shandong Province of China.

RESULTS

Elevated CO2 concentration remarkably increased the abundance of fungivores and significantly decreased their nematode channel ratio (NCR) and enrichment index (EI) irrespective of rice variety (transgenic Bt rice or non-Bt rice) or temperature (normal temperature or increased temperature). Additionally, rice variety and temperature did not significantly change soil nematode composition, abundance and ecological indices (including total maturity index (∑MI), Shannon diversity (H'), structure index (SI), NCR and EI). However, apparent seasonal changes were observed in theses aforementioned variables.

DISCUSSION

These results suggested that atmospheric CO2 concentration but not temperature or rice variety has great impacts on soil nematode community, especially fungivores.

Cultivation Effect of Chitinase-Transgenic Cotton on Functional Bacteria and Fungi in Rhizosphere and Bulk Soil

Background

In consideration for the increasing widespread use of genetically modified (GM) crops, one of the important issues for assessment is the effect of GM crops on soil microbial communities

Objectives

In this study, T₂ chitinase-transgenic cotton (line #57) and its non-transgenic line were investigated for bacterial and fungal dynamics during its development stages.

Material and Methods

The assessments were performed by viable plate count and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) assays.

Results

Viable plate count analysis showed an increase in community structures and the number of culturable bacteria in rhizosphere of both transgenic and non-transgenic cultivars as compared to bulk soil. PCR-DGGE confirmed results of viable plate count assays of the changes in bacterial and fungal communities for all cotton development stages in rhizosphere and bulk zones. No significant differences in number of functional bacteria were observed between rhizosphere soil of chitinase transgenic and non-chitinase transgenic cotton at one particular stage.

Conclusions

The results indicated that T₂ chitinase-transgenic cotton (line #57) might have no adverse effects on community structures and total number of culturable bacteria and fungi in the rhizosphere.

Root and detritus of transgenic Bt crop did not change nematode abundance and community composition but enhanced trophic connections

Transgenic Bacillus thuringensis (Bt) crops are widely deployed to control lepidopterous pests with minimal impact on non-target soil invertebrates. However, most of the results were obtained from field works, the great environmental variation may conceal the small spatial-temporal scaled changes in microhabitats, such as those created near the roots (rhizosphere) or around decomposing residues (detritusphere), which are expected to impact free-living soil organisms more than the bulk soils. The objective of this study was to assess the impact of root and straw residues of transgenic crops on soil, by comparing nematode communities in the rhizosphere (soil microsites only affected by living root), the detritusphere (soil microsites affected by crop aboveground residues) and the rhizosphere-detritusphere interface (soil microsites intensively co-affected by root and residues) of Bt rice and its non-Bt near isoline. Bt rice did not affect nematode abundance and community composition, however, it enhanced the network connections within nematode communities, in both the rhizosphere and detritusphere, indicating the frequency of co-occurring species increased due to the moderate stress of crystal (Cry) as a labile resource of protein or as a moderate pressure of toxic compounds. Furthermore, 60-80% of the correlation between Cry protein (Cry1Ab/Cry1Ac) and nematode genera were positive in the rhizosphere and detritusphere of Bt rice, suggesting that higher Cry protein concentration was associated with the intensive co-occurrence among nematode populations. This finding offers new insights into how the biotic interactions of non-target soil community response to both live and dead parts of transgenic crop, highlighting the moderate stress of Cry protein might affect the community structure and consequent functioning of soil ecosystem based on the elaborately developed knowledge of biotic interactions via ecological network analysis.

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.

Long-term cultivation of Bt rice expressing the Cry1Ab/1Ac gene reduced phytoparasitic nematode abundance but did not affect other nematode parameters in paddy fields

The uncertainty of ecological risks and the effects of growing transgenic Bt rice on the environment hamper its commercial production. Here, soil nematode communities were used as an indicator of soil health and soil food web structure to evaluate the potential effects of growing Bt rice without chemical insecticides for 3years in the paddy field. The nematodes and soil physicochemical properties of Bt rice fields were compared to the near-isogenic control, non-Bt rice fields. A total of 108,363 specimens belonging to 28 different genera were enumerated. The Hirschmanniella, Tobrilus, Dorylaimus and Filenchus were dominant genera. A three-year paddy rice cultivation of Bt rice (Huahui 1) negatively affected the abundance of phytoparasitic nematodes but did not affect the total number of nematodes, the abundance and relative abundance of free-living nematodes, genera richness, diversity indices, soil food web conditions, or community compositions. However, apparent seasonal and inter-annual changes in these variables were observed, indicating that the impact of environmental factors was more stronger than that of the Bt toxin. In conclusion, the potential ecological risks of Bt rice on soil health and sustainability warrant further research to disentangle the impacts from various confounding environmental factors.

Effects of long-term cultivation of transgenic Bt rice (Kefeng-6) on soil microbial functioning and C cycling

Understanding how soil ecosystem responds to transgenic Bacillus thuringiensis (Bt) rice is necessary for environmental risk assessment. While the influences of short-term cultivation of Bt rice on soil properties have been reported previously, little is known about the long-term effects of Bt rice on soil ecosystems. In this study, soil samples were taken from a long-term rice cultivation site in Fujian Province, China, where transgenic Bt rice (Kefeng-6) and its non-Bt parent breed (Minghui-86) had been continuously cultivated for 8 years. Soil Bt protein concentration and a total of 16 variables were analyzed to assess potential risks of soil health under Bt rice cultivation. The results revealed that soil Bt protein is unlikely to accumulate after Bt rice cultivated in the field, and no consistently significant changes were observed in soil enzymatic activities (catalase, dehydrogenase, acid phosphatase, and urease), microbial biomass (microbial carbon and nitrogen), total organic carbon, decomposition (soil respiration, Q₁₀, and qCO₂), soil nitrogen and phosphorus contents. Due to a local tradition that aboveground biomass was removed after harvest, the increased net primary productivity by Bt rice cultivation did not significantly change soil C cycling. Results of this study suggested that on the aspects of soil microbial functioning and C cycling, long-term cultivation of Bt rice is unlikely to result in significant effects on soil health.

A temporal assessment of nematode community structure and diversity in the rhizosphere of cisgenic Phytophthora infestans-resistant potatoes

BACKGROUND

Nematodes play a key role in soil processes with alterations in the nematode community structure having the potential to considerably influence ecosystem functioning. As a result fluctuations in nematode diversity and/or community structure can be gauged as a 'barometer' of a soil's functional biodiversity. However, a deficit exists in regards to baseline knowledge and on the impact of specific GM crops on soil nematode populations and in particular in regard to the impact of GM potatoes on the diversity of nematode populations in the rhizosphere. The goal of this project was to begin to address this knowledge gap in regards to a GM potato line, cisgenically engineered for resistance to Phytophthora infestans (responsible organism of the Irish potato famine causing late blight disease). For this, a 3 year (2013, 2014, 2015) field experimental study was completed, containing two conventional genotypes (cvs. Desiree and Sarpo Mira) and a cisgenic genotype (cv. Desiree + Rpi-vnt1). Each potato genotype was treated with different disease management strategies (weekly chemical applications and corresponding no spray control). Hence affording the opportunity to investigate the temporal impact of potato genotype, disease management strategy (and their interaction) on the potato rhizosphere nematode community.

RESULTS

Nematode structure and diversity were measured through established indices, accounts and taxonomy with factors recording a significant effect limited to the climatic conditions across the three seasons of the study and chemical applications associated with the selected disease management strategy. Based on the metrics studied, the cultivation of the cisgenic potato genotype exerted no significant effect (P > 0.05) on nematode community diversity or structure. The disease management treatments led to a reduction of specific trophic groups (e.g. Predacious c-p = 4), which of interest appeared to be counteracted by a potato genotype with vigorous growth phenotype e.g. cv. Sarpo Mira. The fluctuating climates led to disparate conditions, with enrichment conditions (bacterial feeding c-p = 1) dominating during the wet seasons of 2014 and 2015 versus the dry season of 2013 which induced an environmental stress (functional guild c-p = 2) on nematode communities.

CONCLUSIONS

Overall the functional guild indices in comparison to other indices or absolutes values, delivered the most accurate quantitative measurement with which to determine the occurrence of a specific disturbance relative to the cultivation of the studied cisgenic P. infestans-resistant potatoes.

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.

The fate of fusion Cry1Ab/1Ac proteins from Bt-transgenic rice in soil and water

Toxin proteins form transgenic crops entering into the environment are likely affect non-target organisms. To investigate the entry route and fate of fusion Cry1Ab/1Ac proteins from transgenic rice expressing insecticide toxins from Bacillus thuringiensis (Bt) in soil and water, we conducted greenhouse and field experiments in 2013 and 2014. Cry1Ab/1Ac proteins from Bt-transgenic rice in soil was found within a horizontal range of 25cm, where most of plant roots distributed. Concentration of Cry1Ab/1Ac proteins was lower in water than in soil in the greenhouse experiment, and no Cry1Ab/1Ac protein was detected in field water. Cry1Ab/1Ac concentration from rice straws was higher in ditch water than in distilled water due to the existence of aquatic organisms in ditch water. Bt proteins from transgenic crops enter into soil ecosystems mainly through root exudates and into aquatic ecosystems through plant residues, which determines Bt fate in the environment.

Cry1Ac Transgenic Sugarcane Does Not Affect the Diversity of Microbial Communities and Has No Significant Effect on Enzyme Activities in Rhizosphere Soil within One Crop Season

Cry1Ac transgenic sugarcane provides a promising way to control stem-borer pests. Biosafety assessment of soil ecosystem for cry1Ac transgenic sugarcane is urgently needed because of the important role of soil microorganisms in nutrient transformations and element cycling, however little is known. This study aimed to explore the potential impact of cry1Ac transgenic sugarcane on rhizosphere soil enzyme activities and microbial community diversity, and also to investigate whether the gene flow occurs through horizontal gene transfer. We found no horizontal gene flow from cry1Ac sugarcane to soil. No significant difference in the population of culturable microorganisms between the non-GM and cry1Ac transgenic sugarcane was observed, and there were no significant interactions between the sugarcane lines and the growth stages. A relatively consistent trend at community-level, represented by the functional diversity index, was found between the cry1Ac sugarcane and the non-transgenic lines. Most soil samples showed no significant difference in the activities of four soil enzymes: urease, protease, sucrose, and acid phosphate monoester between the non-transgenic and cry1Ac sugarcane lines. We conclude, based on one crop season, that the cry1Ac sugarcane lines may not affect the microbial community structure and functional diversity of the rhizosphere soil and have few negative effects on soil enzymes.

The presence of Bt-transgenic oilseed rape in wild mustard populations affects plant growth

The adventitious presence of transgenic plants in wild plant populations is of ecological and regulatory concern, but the consequences of adventitious presence are not well understood. Here, we introduced Bacillus thuringiensis Cry1Ac (Bt)-transgenic oilseed rape (Bt OSR, Brassica napus) with various frequencies into wild mustard (Brassica juncea) populations. We sought to better understand the adventitious presence of this transgenic insecticidal crop in a wild-relative plant population. We assessed the factors of competition, resource availability and diamondback moth (Plutella xylostella) infestation on plant population dynamics. As expected, Bt OSR performed better than wild mustard in mixed populations under herbivore attack in habitats with enough resources, whereas wild mustard had higher fitness when Bt OSR was rarer in habitats with limited resources. Results suggest that the presence of insect-resistant transgenic plants could decrease the growth of wild mustard and Bt OSR plants and their populations, especially under high herbivore pressure.