How hibernation and pesticides disturb the bee gut microbiome

August 30, 2022

Bees need their gut microbes too

Without bees on planet Earth, our human population would be in serious trouble. Since bees perform 80% of the global agricultural pollination, in their absence we would lack the pollination of most flowers, fruit and vegetables.

But also bees have microbial helpers that support them in their daily activities. And in bees that live in close contact and in bigger communities – so-called social bees – they constantly exchange their microbes. Indeed, bacteria living in the guts of social bees protect their hosts against harmful pathogens and parasites, help them digest sweet nectar and stimulate their immune systems.

Hence, it seems only obvious that disturbing the gut microbiomes of social bees can dramatically effect bees and their performances. Michelle Hotchkiss, Ph.D. candidate at the University of Ottawa, focuses on the gut microbiomes of bumble bees, which are a specific type of social bee. Interestingly, in many species of bumble bees the queens hibernate during the winter. And during hibernation, their gut microbiomes become naturally disturbed which makes them vulnerable to further disturbance, like that from pesticide exposure.

This is why, Michelle investigates how the gut microbiomes of bumble bee queens change after hibernation along with pesticide-induced disturbances. She is extremely fascinated by this topic since “the health of the queen microbiome is going to affect the health of the microbiome of all workers during the early phase of colony establishment”.

Michelle further explains that “queen bumble bees establish their colonies alone in the spring after hibernation and their gut microbiomes seed the microbiomes of the first batch of workers, so the proper recovery of queen microbiomes after hibernation is very important.”

Interestingly, the core gut microbiota of bumble bees consists only of five anaerobic or microaerophilic bacterial phyla. Yet, these are specifically adapted to the bee gut’s anaerobic environment and their food intake. Since bees mainly consume pollen and nectar, their gut bacteria are able to degrade pectin, the cell wall material of pollen grains, complex carbohydrates and sugars. Also, certain strains contain genes to use sugars that are generally indigestible by the bee or can be even toxic to the insect.

Pesticides disturb bee gut microbiomes

When bees consume nectar or pollen that were treated with pesticides, they will also take up these chemicals. If the pesticides are not readily absorbed by the host, they can come into contact with resident microbes in the gut which can directly affect microbial growth. “As a result, any disturbance in the bee gut microbiome can have real impacts on social bee performance and the pollination services that they provide to floral communities”, says Michelle.

While species from the Bifidobacteriales and Lactobacillales orders both decline in abundance by similar magnitudes after exposure to pesticides, bacteria from the Neisseriales order seem to be resistant to disturbances by pesticides. Interestingly, Bombilactobacillus spp. can increase in abundance by a relatively large magnitude after pesticide exposure. These shifts in the microbiome composition can make bees more susceptible to pathogen infection which can then greatly disturb the cross-feeding activities between different species in the bee gut, thus interfering with microbial and host metabolism as well as bee health and performance.

After exposure to some pesticides, the bee gut microbiome profile can be disturbed for at least seven days. In the life of a working adult bee of 30-40 days, that is a large part of their lives.

Yet, the extent of microbial disturbance by a pesticide depends on its concentration, duration of its exposure, seasonality and concurrent environmental conditions. For bumble bee queens, their gut microbiomes are already disturbed in the spring after hibernation, and so pesticides may be able to cause a more severe disturbance even at a lower concentration or with a short exposure duration. Hence, Michelle finds investigating the bumble bee gut microbiome after hibernation and pesticide exposure incredibly exciting “because we really don’t know a lot about the dynamics of queen gut microbiomes at this crucial stage in the bumble bee life cycle”.

Studying the gut microbiomes of bees

For her experiments, Michelle puts “queens into hibernation and samples them periodically during hibernation and during recovery with or without pesticides”. She then sterilely dissects the guts from the bees before grounding them with a pestle to break them open.

Michelle explains that a big challenge of microbiome research is “the concurrent presence of Gram-positive and Gram-negative bacteria. Gram-positive bacteria, unlike Gram-negative bacteria, are surrounded by a thick peptidoglycan wall and therefore those cells can be more difficult to lyse”. If the chosen lysis method doesn’t take into account the complex nature of microbial samples, more easy-to-lyse microbes like Gram-negative bacteria are cracked and their DNA extracted. This means that the sample “will contain an over-representation of DNA from Gram-negative bacteria that may not reflect the actual microbial abundances of Gram-negative and Gram-positive bacteria in the sample.”

To overcome this challenge in her workflow, Michelle chose the DNeasy PowerLyzer PowerSoil Kit containing a bead beating step with PowerBead tubes and glass beads. “This bead beating step physically disrupts Gram-positive cell walls and ensures that during the chemical lysis step both Gram-negative AND Gram-positive cells will easily break open and the DNA extracts will not be biased towards the Gram-negative members of the community”.

Based on these purified samples, Michelle can perform downstream applications to get reliable insights into her samples. Together, these results will help us take better care of one of the essential helpers of our natural and agricultural communities – pollinating social bees.

Michelle relies on the DNeasy PowerLyzer PowerSoil kit while the upgraded DNeasy PowerSoil Pro Kit now contains zirconia beads of different sizes that allow better disruption of Gram-positive bacteria and fungi. Both kits can be automated on the TissueLyzer II.

About Dr Sarah Wettstadt

Dr Sarah Wettstadt is a microbiologist-turned science writer and communicator working for life science organisations and companies to help them disseminate scientific knowledge. Her overall vision is to empower through learning: she shares scientific knowledge with both scientists and non-scientists and coaches scientists in science communications. Sarah publishes her own blog BacterialWorld to share the beauty of microbes and bacteria, edits and publishes microbiology-research content for the FEMSmicroBlog and co-founded the video platform STEMcognito. Previous to her science communication career, she did her PhD at Imperial College London, UK, and a postdoc in Granada, Spain.