Impact of Glyphosate on the Honey Bee Gut Microbiota: Effects of Intensity, Duration, and Timing of Exposure

Abstract

Exposure to anthropogenic chemicals may indirectly compromise animal health by perturbing the gut microbiota. For example, the widely used herbicide glyphosate can affect the microbiota of honey bees, reducing the abundance of beneficial bacterial species that contribute to immune regulation and pathogen resistance. Previous studies have not addressed how this impact depends on concentration, duration of exposure, or stage of microbiota establishment. Worker bees acquire their microbiota from nestmates early in adult life, when they can also be exposed to chemicals collected by foragers or added to the hives. Here, we investigated how the gut microbiota of honey bees is affected by different concentrations of glyphosate and compared the effects with those caused by tylosin, an antibiotic commonly used to treat hives. We treated newly emerged workers at the stage at which they acquire the microbiota and also workers with established gut microbiota. Treatments consisted of exposure to sucrose syrup containing glyphosate in concentrations ranging from 0.01 mM to 1.0 mM or tylosin at 0.1 mM. Based on 16S rRNA amplicon sequencing and quantitative PCR (qPCR) determination of abundances, glyphosate perturbed the gut microbiota of honey bees regardless of age or period of exposure. Snodgrassella alvi was the most affected bacterial species and responded to glyphosate in a dose-dependent way. Tylosin also perturbed the microbiota, especially at the stage of acquisition, and the effects differed sharply from the effects of glyphosate. These findings show that sublethal doses of glyphosate (0.04 to 1.0 mM) and tylosin (0.1 mM) affect the microbiota of honey bees. IMPORTANCE As is true of many animal species, honey bees depend on their gut microbiota for health. The bee gut microbiota has been shown to regulate the host immune system and to protect against pathogenic diseases, and disruption of the normal microbiota leads to increased mortality. Understanding these effects can give broad insights into vulnerabilities of gut communities, and, in the case of honey bees, could provide information useful for promoting the health of these economically critical insects, which provide us with crop pollination services as well as honey and other products. The bee gut microbiota is acquired early in adult life and can be compromised by antibiotics and other chemicals. The globally used weed killer glyphosate was previously found to impact the gut microbiota of honey bees following sustained exposure. In the present study, we address how this impact depends on concentration, duration of exposure, and stage of community establishment. We found that sublethal doses of glyphosate reduce the abundance of beneficial bacteria and affect microbial diversity in the guts of honey bees, regardless of whether exposure occurs during or after microbiota acquisition. We also compared the effects of glyphosate to those of tylosin, an antibiotic used in beekeeping, and observed that tylosin effects diverge from those caused by glyphosate and are greater during microbiota acquisition. Such perturbations are not immediately lethal to bees but, depending on exposure level, can decrease survivorship under laboratory conditions.

Oral or Topical Exposure to Glyphosate in Herbicide Formulation Impacts the Gut Microbiota and Survival Rates of Honey Bees

“…Unfortunately, this precludes any comparisons between the glyphosate concentrations detected in our experiments with concentrations detected in honey in other studies (44)(45)(46)(47), but it does show that bees can directly transfer contaminated resources to hive compartments. A recent study using bees under laboratory conditions showed that glyphosate has a persistent impact on the gut microbiota of young adult workers whether exposure occurs during or after microbiota establishment and that this impact is dose dependent (88).…”

Could Glyphosate and Glyphosate-Based Herbicides Be Associated With Increased Thyroid Diseases Worldwide?

“…The glyphosate mechanism of action is through inhibition of the growth of weeds by interfering with the production of essential aromatic amino acids by inhibiting EPSPS, which is responsible for chorismate biosynthesis, an intermediate in the biosynthesis of phenylalanine, tyrosine and tryptophan (7). Then, from the moment glyphosate inhibits it, these bacteria are unable to maintain normal levels in the gut microbiome (111,(113)(114)(115). Thus, new studies evaluating the involvement of the gut-thyroid axis are relevant in advancing the knowledge of glyphosate toxicity on thyroid function.…”

“…This is corroborated by studies where gut microbiota dysbiosis was correlated to Hashimoto’s thyroiditis ( 102 – 104 ), Graves’ disease ( 104 ), thyroid cancer and thyroid nodules ( 105 ). In parallel in the field of toxicology, recent studies indicate that GBH is able to affect the intestinal microbiome of mice ( 106 ), rats ( 107 – 112 ), honeybees ( 113 , 114 ), Japanese quails ( 115 ) and Daphnia magna ( 116 ). A possible explanation for this toxicity is that some classes of bacteria require the shikimate pathway (5-enolpyruvylshikimate-3-phosphate synthase, EPSPS) for their metabolism.…”

Impact of Chronic Exposure to Sublethal Doses of Glyphosate on Honey Bee Immunity, Gut Microbiota and Infection by Pathogens

“…Recent studies have shown that glyphosate alters the structure and composition of the honey bee gut microbiota through the inhibition of the EPSPS enzyme, which can be coded by the genome of several microorganisms [ 15 , 16 , 17 , 18 ]. The gut microbiota plays an important role in honey bee metabolism, growth, development, immunity and defense against pathogens [ 19 , 20 ], so alterations of this community (dysbiosis) could have severe consequences on honey bee health.…”