Abstract
The honeybee (Apis mellifera) has to cope with multiple environmental stressors, especially pesticides. Among those, the herbicide glyphosate and its main metabolite, the aminomethylphosphonic acid (AMPA), are among the most abundant and ubiquitous contaminant in the environment. Through the foraging and storing of contaminated resources, honeybees are exposed to these xenobiotics. As ingested glyphosate and AMPA are directly in contact with the honeybee gut microbiota, we used quantitative PCR to test whether they could induce significant changes in the relative abundance of the major gut bacterial taxa. Glyphosate induced a strong decrease in Snodgrassella alvi, a partial decrease of a Gilliamella apicola and an increase in Lactobacillus spp. abundances. In vitro, glyphosate reduced the growth of S. alvi and G. apicola but not Lactobacillus kunkeei. Although being no bee killer, we confirmed that glyphosate can have sublethal effects on the honeybee microbiota. To test whether such imbalanced microbiota could favor pathogen development, honeybees were exposed to glyphosate and to spores of the intestinal parasite Nosema ceranae. Glyphosate did not significantly enhance the effect of the parasite infection. Concerning AMPA, while it could reduce the growth of G. apicola in vitro, it did not induce any significant change in the honeybee microbiota, suggesting that glyphosate is the active component modifying the gut communities.
Highlights
Glyphosate, or N-(phosphonomethyl)glycine, is as a broad-spectrum herbicide used for weed control
To verify the effect of glyphosate on the microbiota, a second experiment was performed on summer honeybees that were chronically exposed to 1.5 mM and 7.5 mM of glyphosate, of aminomethylphosphonic acid (AMPA) and of stoichiometric mixtures of both xenobiotics
The data confirmed previous studies showing that glyphosate is no bee killer [11,13,19,21,22,23] and showed that it is true for AMPA
Summary
Glyphosate, or N-(phosphonomethyl)glycine, is as a broad-spectrum herbicide used for weed control. It blocks the plant growth by inhibiting the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme of the shikimate pathway involved in the synthesis of aromatic metabolites, including aromatic amino acids [1,2]. The EPSPS is present in plants and in bacteria and fungi, but not in metazoans. Glyphosate is the most sprayed herbicide worldwide, especially under commercial formulations, the best known being Roundup. The frequency and intensity of glyphosate application as well as the surface of treated croplands have been growing constantly, especially since the marketing of Genetically Engineered Herbicide-Tolerant (GE-HT) crops.
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