No abstract

Pesticides are increasing honeybee (Apis mellifera) death rates globally. Clothianidin neonicotinoid appears to impair the microbe–immunity axis. We conducted cage experiments on newly emerged bees that were 4–6 days old and used a 16S rRNA metataxonomic approach to measure the impact of three sublethal clothianidin concentrations (0.1, 1 and 10 ppb) on survival, sucrose syrup consumption and gut microbiota community structure. Exposure to clothianidin significantly increased mortality in the three concentrations compared to controls. Interestingly, the lowest clothianidin concentration was associated with the highest mortality, and the medium concentration with the highest food intake. Exposure to clothianidin induced significant variation in the taxonomic distribution of gut microbiota activity. Co-abundance network analysis revealed local dysbiosis signatures specific to each gut section (midgut, ileum and rectum) were driven by specific taxa. Our findings confirm that exposure to clothianidin triggers a reshuffling of beneficial strains and/or potentially pathogenic taxa within the gut, suggesting a honeybee’s symbiotic defense systems’ disruption, such as resistance to microbial colonization. This study highlights the role of weak transcriptional activity taxa in maintaining a stable honeybee gut microbiota. Finally, the early detection of gut dysbiosis in honeybees is a promising biomarker in hive management for assessing the impact exposure to sublethal xenobiotics.

Including probiotics in honeybee nutrition represents a promising solution for mitigating diseases, and recent evidence suggests that various microbes possess mechanisms that can bioremediate environmental pollutants. Thus, the use of probiotics capable of degrading pesticides used in modern agriculture would help to both reduce colony losses due to the exposure of foragers to these toxic molecules and improve honeybee health and wellbeing globally. We conducted in vitro experiments to isolate and identify probiotic candidates from bacterial isolates of the honeybee gut (i.e., endogenous strains) according to their ability to (i) grow in contact with three sublethal concentrations of the pesticide clothianidin (0.15, 1 and 10 ppb) and (ii) degrade clothianidin at 0.15 ppb. The isolated bacterial strains were indeed able to grow in contact with the three sublethal concentrations of clothianidin. Bacterial growth rate differed significantly depending on the probiotic candidate and the clothianidin concentration used. Clothianidin was degraded by seven endogenous honeybee gut bacteria, namely Edwardsiella sp., two Serratia sp., Rahnella sp., Pantoea sp., Hafnia sp. and Enterobacter sp., measured within 72 h under in vitro conditions. Our findings highlight that endogenous bacterial strains may constitute the base material from which to develop a promising probiotic strategy to mitigate the toxic effects of clothianidin exposure on honeybee colony health.

BackgroundHoneybees (Apis mellifera) are facing a number of interacting stress factors affecting their general health as well as their nervous and immune systems. Recent evidence proposed the clothianidin neonicotinoid as a potential disrupting factor for the microbiota-immunity axis. In this research, we conducted in vivo experiments to measure the impact of three sublethal clothianidin concentrations (0.1, 1 and 10 ppb) on honeybee survival, syrup consumption and the honeybee gut microbiota dysbiosis. Results Clothianidin exposure significantly increased mortality in the three concentrations compared to controls. Interestingly, the lowest clothianidin concentration was associated to the highest food intake and the highest mortality. Clothianidin exposure significantly induced variation in the taxonomic composition of the gut microbiota. The co-abundance network analysis reveals local dysbiosis signatures specific to each gut cohorts (midgut, ileum and rectum) driven by specific taxa.Conclusions Our findings confirm that clothianidin exposure triggers a disruption of the honeybee’s symbiotic defense systems such as resistance to colonization, translating into a surge of potentially pathogenic taxa. Furthermore, the importance of low activity taxa with weak transcriptional activity in maintaining a stable honeybee gut microbiota. Finally, the early detection of gut dysbiosis in honeybee is an early promising alarming signal towards a microbiome approach in hive management the impact for assessing the impact of sublethal xenobiotics exposure.