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Daphnia Fed with Bt Maize Leaves Show Chronic Responses

The second most common trait of genetically modified (GM) plant is insect resistance. This is usually obtained by introducing, into the plant’s genome, genes from the bacterium Bacillus thuringiensis (Bt), which produce insecticidal proteins. A new study has compared the quality of a GM insect-resistant maize (MON810) and its appropriate non-GM near-isoline counterpart as feed for Daphnia magna (a water flea) and found significant differences.

D. magna fed with the Bt maize leaves displayed a significantly smaller body size as well as reduced fecundity later in the life cycle, indicating increased stress levels, compared to those fed non-Bt leaves. They reproduced approximately 20% less offspring.

This is the first study to examine GM-plant leaf material in the D. magna model and provides evidence of negative fitness effects of a GM maize hybrid on a non-target model organism under chronic, high dietary exposure. The scientists postulate that the transgenic proteins exert a non-target effect in D. magna and/or unintended changes were produced in the maize genome by the transformation process, producing a nutritional difference between GM-maize and non-GM near-isoline.

The scientists call for further studies over the full life cycle of model organisms, considering that important biological effects may only be detected after chronic exposure. Furthermore, they highlight the importance of conducting safety testing for GM plants with plant material and plant-produced recombinant proteins, rather than with microbially produced recombinant proteins.
The Abstract and Conclusions of the paper are reproduced below.

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CHRONIC RESPONSES OF DAPHNIA MAGNA UNDER DIETARY EXPOSURE TO LEAVES
OF A TRANSGENIC (EVENT MON810) Bt–MAIZE HYBRID AND ITS CONVENTIONAL
NEAR-ISOLINE

Daniel Ferreira Holderbaum, Marek Cuhra, Fern Wickson, Afonso Inácio Orth, Rubens Onofre Nodari, Thomas Bøhn

Journal of Toxicology and Environmental Health, Part A, 78A new study has found significant negative chronic effects in Daphnia fed with GM insect-resistant maize leaves such as smaller body size, reduced growth and decreased fertility.93–1007, 2015

http://www.ncbi.nlm.nih.gov/pubmed/26262442

Abstract

Insect resistance is the second most common trait globally in cultivated genetically modified (GM) plants. Resistance is usually obtained by introducing into the plant’s genome genes from the bacterium Bacillus thuringiensis (Bt) coding for insecticidal proteins (Cry proteins or toxins) that target insect pests. The aim of this study was to examine the hypothesis that a chronic, high-dose dietary exposure to leaves of a Bt–maize hybrid (GM event MON810, expressing a transgenic or recombinant Cry1Ab toxin), exerted no adverse effects on fitness parameters of the aquatic nontarget organism Daphnia magna (water flea) when compared to an identical control diet based on leaves of the non-GM near-isoline. Cry1Ab was immunologically detected and quantified in GM maize leaf material used for Daphnia feed. A 69-kD protein near Bt’s active core-toxin size and a 34-kD protein were identified. The D. magna bioassay showed a resource allocation to production of resting eggs and early fecundity in D. magna fed GM maize, with adverse effects for body size and fecundity later in life. This is the first study to examine GM-plant leaf material in the D. magna model, and provides of negative fitness effects of a MON810 maize hybrid in a non-target model organism under chronic, high dietary exposure. Based upon these results, it is postulated that the observed transgenic proteins exert a nontarget effect in D. magna and/or unintended changes were produced in the maize genome/metabolome by the transformation process, producing a nutritional difference between GM-maize and non-GM near-isoline.

Conclusions

This study explored chronic effects of high dietary exposure of an aquatic nontarget organism to leaves of a MON810 GM Bt–maize hybrid, in comparison to its non-GM near isoline. The GM Bt–maize diet resulted in increased ephippia (resting eggs) production, along with reductions in growth and fecundity later in the life cycle of our test organism, D. magna, indicating increased stress levels in animals fed GM Bt–maize leaves. It is postulated that the transgenic protein and/or unintended transformation-related changes in the expressed maize genome/metabolome were the causes for observed effects. Further studies are necessary to more precisely determine the mechanism or mechanisms underlying the sublethal fitness effects observed in D. magna exposed to Bt–maize leaves. Data indicate that effects of GM feed and food materials intended for lifelong consumption need to be tested on multiple endpoints, preferably over the full life cycle of model organisms, considering that important biological effects may only be detected after chronic exposure.

Further, unique characteristics detected in the recombinant Cry1Ab of MON810 Bt–maize, as opposed to bacterially produced Cry1Ab, raise serious questions concerning whether microbial produced recombinant proteins are adequate for assessing risks posed by recombinant plant proteins. This highlights the importance of conducting safety testing for GM plants with plant material and plant-produced recombinant proteins, coupled to a case-by case approach to GM-plant toxicity testing, in order to achieve more reliable accuracy in effect size and uncertainty estimation, and to contribute to the establishment of a more precise risk profile for specific GM plants/events.