College of Science

58 Pollinator Influence on the Abundance and Composition of Nectar Microbes in Oenothera Macrocarpa

Eleanor Wachtel (University of Utah); Joshua Steffen (School of Biological Sciences, University of Utah); and Annika Kloepper (University of Utah)

Faculty Mentor: Joshua Steffen (School of Biological Sciences, University of Utah)


Pollination is a crucial step in plant reproduction, essential for the cultivation of 80% of the 1400 crop plants grown around the world (1). Insects, specifically bees, play an integral role in the process by transferring pollen from one flower to another while taking advantage of energy sources, primarily in the carbohydrate rich nectar produced by flowers (2). These interactions between pollinators and energy sources are critical for effective pollination. Current research suggests that microbial communities in nectar can influence interactions between flowers and pollinators (3-5). Our research attempts to refine our understanding regarding the impact of foraging insects on microbial abundance and diversity in floral nectar.

We characterized microbial communities in Oenothera macrocarpa (evening primrose) because of its abundance of nectar, its day-long life span, and its large quantity of pollinating insect species. Our preliminary research identified several microbial species that colonize nectar. In order to see whether the pollinators visiting the O. macrocarpa species were depositing microbes, we limited pollination through bagging the flowers for their whole life cycle (from bud to wilted flower). We then extracted nectar from both the limited (bagged) and unlimited (open) flowers and cultured the microbes on two different media, LB and Nectar. The nectar media was used because of its ability to mimic the environment the microbes usually grow in, and the two different media types were used to foster non-redundant, differing growth of microbes. After a two-day incubation period, we counted the colonies grown on both media for both conditions (bagged and unbagged). We ran PCR, or polymerase chain reaction, on the colonies, using the conserved 16S region of the bacterial genome to identify the microbes. We found that open, pollinated flowers harbored a greater number of microbes relative to flowers that insect visitation was prohibited (one-sided, unpaired t-test, p-values < .05). Similarly, our data suggests a difference in the microbial diversity in nectar between bagged and unbagged flowers. A total of fifteen different taxonomic groups were identified from both the open and bagged floral nectar. However, in unbagged, pollinated flowers, eleven different taxa were identified while in bagged, unpollinated flowers only seven were identified. A number of taxa (i.e. Acinetobacter, Curtobacterium, and Enterobacterales) were only cultured from open flower nectar. These results generally align with previous research findings in alternative species and environments.

Our experiments confirm that foraging has a significant impact on the microbial diversity in nectar and suggests that this composition is directly related to the pollinators that visit this species. Further research will attempt to associate bacteria taxa to specific pollinator genera, in an effort to use the presence of particular microbial species to indicate and identify pollinator visitation in the absence of direct pollinator observation. Additionally, future work will focus on determining the impact of bacteria on chemical cues accompanying nectar and associated foraging preferences.


Why is Pollination Important? U.S. Forest Service. (n.d.). Retrieved August 2, 2022, from

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Keller, A., McFrederick, Q. S., Dharampal, P., Steffan, S., Danforth, B. N., & Leonhardt, S. D. (2021). (More than) Hitchhikers through the network: the shared microbiome of bees and flowers. Current opinion in insect science, 44, 8–15.

Cullen, N. P., Fetters, A. M., & Ashman, T. L. (2021). Integrating microbes into pollination. Current opinion in insect science, 44, 48–54.

Rebolleda-Gómez, M., Forrester, N. J., Russell, A. L., Wei, N., Fetters, A. M., Stephens, J. D., & Ashman, T. L. (2019). Gazing into the anthosphere: considering how microbes influence floral evolution. The New phytologist, 224(3), 1012–1020.

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RANGE: Undergraduate Research Journal Copyright © 2022 by Eleanor Wachtel (University of Utah); Joshua Steffen (School of Biological Sciences, University of Utah); and Annika Kloepper (University of Utah) is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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