Maya Cabrera ’27
The honey bee gut is commonly used model for studying host–microbe interactions, and is divided into three main sections: the foregut, the midgut, and the hindgut, which contains the ileum and rectum. Each region harbors a distinct community of microbes that together form a conserved microbiota essential for bee health (Motta & Moran, 2023). Among these bacterial species, Snodgrassella alvi wkB2 resides in the ileum, where it acts as an ecosystem engineer. By lowering pH and oxygen levels, S. alvi creates conditions that allow other bacterial species to colonize effectively, making it an essential pioneer species in gut community assembly.
Dr. Korin Rex Jones, my summer mentor and a Stengyl-Wyer Postdoctoral Fellow at the University of Texas at Austin, chose S. alvi as the focal organism for his work because of its ecological importance, relative ease of culturing, and the availability of genetic and experimental tools. S. alvi is also intriguing because it employs a complex system known as the Type VI
Secretion System (T6SS). This syringe-like structure allows bacteria to inject toxic effector proteins directly into neighboring cells, either killing competing strains or modulating host immunity (Motta et al., 2024). Recent evidence suggests that T6SS-1 is primarily used for intraspecific competition, while T6SS-2/3 plays a role in communication with the host immune system. The diversification of these T6SS toxins across bee gut microbes points to a long evolutionary history of microbial antagonism, in which lineages have repeatedly adapted to outcompete close relatives (Steele et al., 2017). Thus, S. alvi represents both a keystone of microbiome stability and a window into ancient microbial conflict.
Our first project examined strain-level variation in S. alvi across hives and over time. While the honey bee gut microbiota is consistent at the species level, significant variation exists among strains (Motta & Moran, 2023). We asked whether S. alvi strains change seasonally or differ across social and environmental contexts.
From April 2025 to July 2025, we collected bees monthly from three locations: Beevo (3 hives), Driftwood (4 hives), and Patterson (8 hives). We dissected 50 bees per hives in sets of five, with each group homogenized in PBS to produce ten pooled gut samples. In total, we dissected 3,100 bees. Because each S. alvi strain carries a unique version of the minD gene, we can use PCR amplification with barcoded primers to identify strain-specific variants. Sequencing and comparing these markers to reference databases will allow us to map the diversity of S. alvi strains across time and hive conditions. This survey is more than a cataloging effort, it asks whether strain composition reflects stability or flexibility in the face of environmental shifts. Understanding this variability is crucial for predicting how bee gut communities respond to agricultural practices and ecological stressors.
Our second project focused on priority effects, an ecological principle describing how the order and timing of microbial colonization influence which species establish and persist. In any environment, organisms occupy specific niches and often compete both interspecifically and intraspecifically. In microbiomes, the species that arrive first can strongly shape which microbes successfully colonize later, either facilitating or inhibiting their establishment (Fukami, 2015;Jones et al., 2023). Understanding these dynamics is particularly relevant for honey bees, as modern agriculture and beekeeping practices, such as antibiotic or acaricide use, can unintentionally disrupt the gut microbiome, with consequences for bee health. Designing interventions with the microbiome in mind provides an alternative approach to maintaining hive health. For example, previous work has shown that an engineered S. alvi wkB2 strain can kill mites without harming the native gut community (Leonard et al., 2020). However, to be effective in real-world conditions, it is critical to know whether this engineered strain can establish itself in the presence of other microbes.
We hypothesized that wkB2 would establish successfully in microbiota-deprived bees, such as pupae, due to priority effects. The more challenging questions were whether it could establish alongside other bacteria or when other strains had already colonized. These scenarios are especially important because in practical hive applications, we cannot control when individual bees ingest the engineered strain—some may have no microbiome, others a partially formed microbiome, and others a fully established microbial community. If wkB2 cannot establish under these variable conditions, the intervention would fail.
To test these questions, we reared microbiota-deprived bees from pupae collected at the indigo eye-color and dark peach body stage, and divided them into treatment groups. Treatments included a control (sugar water + PBS), wkB2 alone (engineered to be fluorescent and kanamycin-resistant), gut homogenate (GH) from five adult bees, and combinations in sequence: wkB2 followed by GH, GH followed by wkB2, and simultaneous wkB2 + GH. Sequential treatments were administered with the second treatment given the following day. After four days, we dissected and homogenized each bee individually and plated serial dilutions on CBA and Kan CBA media in triplicate. Colony-forming units were counted after two days, and wkB2 presence was confirmed under blue light.
Our results highlighted the importance of colonization order. When GH was introduced first, wkB2 colonization was suppressed, likely due to competition from resident S. alvi strains in the GH. This antagonism is consistent with the strain’s Type VI Secretion System, which mediates bacterial competition (Steele et al., 2017; Motta et al., 2024). By contrast, when wkB2 colonized before GH, its abundance exceeded baseline levels observed when introduced alone, suggesting that early establishment conferred a competitive or facilitative advantage. Simultaneous introduction had little effect on wkB2 abundance, suggesting that priority effects, rather than mere co-presence, drive colonization outcomes. Pollen supplementation had no measurable effect on wkB2 abundance, confirming that diet was not a major factor in these experiments.
These findings demonstrate that microbiome assembly is shaped by historical contingencies and competition. For applied interventions, such as engineered wkB2 strains designed to protect bees from mites, it is critical to consider these dynamics: if the strain cannot establish in variable microbial environments, its efficacy will be limited. Moving forward, to further dissect the mechanisms underlying wkB2 colonization, Dr. Jones plans to test knockout mutants of its two T6SS systems: T6SS-1, which mediates competition with other bacteria, andT6SS-2/3, which facilitates host communication. These experiments will reveal how microbial warfare and host interaction jointly influence strain establishment in the bee gut.
Beyond the technical work, the implications for sustainability are clear. Modern agriculture and apiculture practices frequently disrupt bee microbiomes through chemical exposures, including antibiotics, acaricides, fungicides, herbicides, and insecticides (Motta & Moran, 2023). Overuse of these treatments can diminish beneficial gut bacteria in adult worker bees, increasing mortality and susceptibility to pathogens. For example, field-realistic exposure to tylosin impairs honey bee microbiota and heightens pathogen vulnerability, though these effects can be mitigated by supplementing with native gut probiotics (Powell, Carver, Leonard, & Moran, 2021). Developing microbiome-informed interventions, such as targeted probiotics that stabilize gut communities, offers a promising path to support pollinator health while reducing reliance on chemical treatments.
This summer reshaped how I think about science. Early on, I struggled with bee dissections and triplicate plating. Failures were frequent, but each forced me to refine my technique and adapt my approach. Precision, I learned, emerges through iteration. Just as microbes adjust to their environment, scientists must also remain flexible in the face of challenges. Working at the interface of microbiology and ecology deepened my curiosity about how microbes influence immunity and behavior across species. For other students considering similar opportunities, my advice is to embrace uncertainty and iteration. Science rarely unfolds linearly; it advances through persistence, adaptability, and an eye for the broader impact. In the end, even the smallest details of a gut dissection connect to global challenges in agriculture, ecology, and sustainability. Research at the molecular scale can ripple outward, shaping not only microbiomes, but the future of our food systems. And importantly, these insights extend beyond bees: a deeper understanding of gut microbiome assembly and colonization dynamics in insects may also inform strategies for human health. Just as engineered strains could one day stabilize bee gut communities, similar approaches might eventually be applied to human microbiomes—offering new possibilities for treating disease, enhancing immunity, and promoting resilience in healthcare.
Maya Cabrera is a guest contributor to the Princeton Medical Review. She is also an undergraduate research assistant at Princeton University studying host–symbiont interactions in the Graham and Kocher Labs, where her work focuses on Acrostichus nematodes and two species of sweat bees (Augochlorella aurata and Augochlora pura). She also serves as co-president of Princeton’s Bee Team, helping to take care of and educate others about honey bees. Additionally, Maya plans to pursue a Ph.D. exploring how immune processes and animal behavior influence one another across species. She can be reached at mc6795@princeton.edu.
References
Fukami, T. (2015). Historical contingency in community assembly: Integrating niches, species
pools, and priority effects. Annual Review of Ecology, Evolution, and Systematics, 46(1),
1–23. https://doi.org/10.1146/annurev-ecolsys-110411-160340
Jones, K. R., Song, Y ., Rinaldi, S. S., & Moran, N. A. (2023). Effects of priority on strain-level
composition of the honey bee gut community. mBio.
Leonard, S. P., Powell, J. E., Perutka, J., Geng, P., Heckmann, L. C., Horak, R. D., Davies, B. W.,
Ellington, A. D., Barrick, J. E., & Moran, N. A. (2020). Engineered symbionts activate
honey bee immunity and limit pathogens. Science, 367(6477), 573–576.
https://doi.org/10.1126/science.aax9039
Motta, E. V . S., & Moran, N. A. (2023). The honeybee microbiota and its impact on health and
disease. Nature Reviews Microbiology. https://doi.org/10.1038/s41579-023-00990-3
Motta, E. V . S., Lariviere, P. J., Jones, K. R., Song, Y ., & Moran, N. A. (2024). Type VI secretion
systems promote intraspecific competition and host interactions in a bee gut symbiont.
Proceedings of the National Academy of Sciences, 121(44), e2414882121.
https://doi.org/10.1073/pnas.2414882121
Powell, J. E., Carver, Z., Leonard, S. P., & Moran, N. A. (2021). Field-realistic tylosin exposure
impacts honey bee microbiota and pathogen susceptibility, which is ameliorated by native
gut probiotics. Microbiology Spectrum, 9(1), e00103-21.
https://doi.org/10.1128/spectrum.00103-21
Steele, M. I., Kwong, W. K., Whiteley, M., & Moran, N. A. (2017). Diversification of Type VI
Secretion System toxins reveals ancient antagonism among bee gut microbes. mBio, 8(6),
e01630-17. https://doi.org/10.1128/mBio.01630-17
Leave a Reply