Host-associated microbial communities, also known as microbiomes, are essential to the health of their hosts, and disturbance of these communities can negatively impact host fitness. The honey bee gut microbiome is a relatively simple host-associated community that makes an excellent model system for studying microbiome stability. In addition, honey bees are essential agricultural pollinators, so factors that impact their health are important for food security. The presented research focused on the stability of the honey bee gut microbiome in response to disturbance from the antibiotic tetracycline. Tetracycline was chosen because it is the most commonly used antibiotic in beekeeping, and may have negative effects on bees through the disruption of their gut microbiomes. The first study presents a new fecal sampling method for studying the honey bee gut microbiome of individual bees over time. This method accurately represented bacterial community structure in the gut microbiome as determined with 16S rRNA gene amplicon sequencing, as fecal and whole gut samples did not differ significantly for individual bees. The fecal sampling technique was then used to examine changes to individual honey bee gut bacterial communities before and after tetracycline exposure. Minimal differences in gut community structure were detected prior to and five days after tetracycline treatment. However, there was variability in how individual gut microbiomes were affected by tetracycline treatment, highlighting the importance of intraspecific variation in response to disturbance. The second study investigated whether the timing of disturbance during a host's life impacts microbiome community stability. Newly emerged bees were treated with tetracycline, returned to their hive, and recollected 7 or 14 days later. The gut communities of the bees were then characterized using 16S rRNA gene amplicon sequencing. Gut microbiome structure of bees treated with tetracycline at emergence differed from controls both 7 and 14 days after emergence, with the antibiotic-treated bees having lower community richness overall. This study showed that early life disturbance of host-associated microbial communities can influence microbiome structure later in life. The final study describes the occurrence of antibiotic resistance genes (ARGs) in honey bee gut bacterial symbionts from hives across the US. Honey bee gut metagenomes were sampled from hives at 13 apiaries located in a transect from Virginia to Washington, and ARG presence was assessed across the sites. We also specifically quantified the abundances of two common tetracycline resistance genes (tet(B) and tet(M)) across apiaries. ARGs, both for antibiotics used in beekeeping and unrelated antibiotics, were detected in honey bee gut bacteria from all apiaries. Tetracycline resistance genes were the most common across all apiaries, and the abundance of two tetracycline resistance genes varied by apiary. Members of the honey bee gut microbiome contained different proportions of ARGs, but taxa within a single family contained similar proportions, possibly indicating phylogeny plays a role in ARG accumulation. In particular, Gilliamella and Frischella, both in the family Orbaceae, contained the highest percentages of ARGs. The results from this study suggest honey bee bacteria act as reservoirs of ARGs. Overall, the presented research contributes to the field of biology by highlighting the importance of intraspecific variation in host-associated microbial communities and presenting a new method for studying honey bee gut microbiome variation at the individual-level, showing that early life events in honey bees influence microbiome development, and suggesting that honey bee bacterial symbionts have adapted to deal with antibiotic disturbance through the accumulation of ARGs. / Doctor of Philosophy / Nearly all animals, including honey bees, have communities of bacteria that live on and in them. These communities, called microbiomes, are often essential to the health of their hosts. For instance, communities of gut bacteria can be important for breaking down food for digestion. Honey bees have approximately 10 bacterial species that consistently live in their guts and provide these types of services to their host. As with many bacterial communities, these beneficial bacteria can be impacted by exposure to antibiotics, even though antibiotics can also be important for treating or preventing dangerous bacterial infections. In honey bee hives, the antibiotic tetracycline is used to prevent bacterial disease. However, tetracycline may simultaneously be negatively impacting colony health through disruption of the honey bee gut microbiome. The goal of the presented work was to understand how tetracycline impacts the honey bee gut microbiome. In my first chapter, I demonstrate a new fecal sampling method that will allow us to understand how gut microbiomes from individual bees change over time. I first compared the bacteria found in fecal samples to those in the whole guts of bees and found that the bacterial communities of the fecal samples and guts were very similar, indicating that fecal sampling is a good method for studying the honey bee gut microbiome. I then used my fecal sampling method to determine how individual honey bee gut microbiomes respond to antibiotic disturbance over time. I collected fecal samples from adult bees prior to treatment, treated the bees with tetracycline, and after five days of being maintained in the lab, recollected fecal samples. My results showed few changes to the bacterial communities before and after treatment, suggesting some honey bee gut microbiomes may be resistant to tetracycline. In my second chapter, I addressed whether exposure to antibiotics early in life had long-term impacts on the gut microbiome. I treated bees at the start of adulthood with tetracycline, returned the bees to their hive for 7 or 14 days, and assessed their microbiome. Tetracycline treatment at the beginning of adulthood changed the gut microbiome later in life, as the microbiomes of tetracycline-treated bees and controls differed from one another both 7 and 14 days after exposure. This chapter shows that disturbances to microbiomes during early life can also affect microbiomes later. My third chapter addressed how honey bee bacteria have adapted to antibiotic use by identifying antibiotic resistance genes (ARGs) in honey bee gut bacteria from 13 hives located in a transect across the US from the state of Washington to Virginia. I found a variety of antibiotic resistance genes in honey bee gut bacteria, both associated with beekeeping and likely environmental contamination. The prevalence of antibiotic resistance genes in honey bee bacteria may help us track antibiotic resistance in the environment. Ultimately, my dissertation contributes to our understanding of how antibiotic use affects honey bees by changing their gut microbiome.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/118928 |
| Date | 08 May 2024 |
| Creators | Gregory, Casey L. |
| Contributors | Biological Sciences, Belden, Lisa Kay, Haak, David C., Moore, Ignacio T., Fell, Richard D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
Page generated in 0.0135 seconds