Microbial co-occurrence in floral nectar affects metabolites and attractiveness to a generalist pollinator

Authors: Rering, Caitlin; VANNETTE, RACHEL - University Of California, Davis; SCHAEFFER, ROBERT - Utah State University; Beck, John

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 4/3/2020
Citation: Rering, C.C.; Vannette, R.L.; Schaeffer, R.N.; Beck, J.J. Microbial co-occurrence in floral nectar affects metabolites and attractiveness to a generalist pollinator. J. Chem. Ecol. 2020, 46, 659-667. https://doi.org/10.1007/s10886-020-01169-3.
DOI: https://doi.org/10.1007/s10886-020-01169-3

Interpretive Summary: Microbial growth and metabolism within a food source can have important influences on insect attraction to the food source. Microbial communities are often comprised of multiple microbe species; however, studies of insect-microbe interactions often focus on single microbial systems (monocultures). Such an approach is unlikely to predict effects of multiple microbial systems, which are often found in natural systems. USDA-ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology, in collaboration with scientists from the University of California, Davis, and Utah State University used two common nectar-inhabiting microorganisms, the yeast Metschnikowia reukaufii and the bacterium Asaia astilbes, to evaluate and compare affects of microbial monocultures and cocultures (two or more microbes) on their odor and chemical composition production, growth in nectar, and influences on pollinator foraging across two nectar concentrations. Co-inoculation of the microbes decreased the abundance of the yeast, but not the abundance of the bacterium. Emitted odors differed strongly between microbial inoculations, while sugar and amino acid contents (chemical composition) were relatively similar among co- and monocultures. Honey bees consumed the mono- and cocultures at similar levels, and on average 40% more sterile control. A. astilbes-inoculated nectars were removed compared to that of M. reukaufii or coculture nectar. These results suggest that multiple microbes within the nectar can influence odors emitted, as well as pollinator preference. This study is foundational regarding microbe-influenced chemical consequences to the nectar, and consequential behavior effects to pollinators.

Technical Abstract: Microbial metabolism can shape cues important for animal attraction in service-resource mutualisms. Resources are frequently colonized by microbial communities, but experimental assessment of animal-microbial interactions often focus on microbial monocultures. Such an approach likely fails to predict effects of microbial assemblages, as microbe-microbe interactions may affect in a non-additive manner microbial metabolism and resulting chemosensory cues. Here, we compared effects of microbial mono- and cocultures on growth of constituent microbes, volatile metabolite production, sugar catabolism, and effects on pollinator foraging across two nectar environments that differed in sugar concentration. Growth in co-culture decreased the abundance of the yeast Metschnikowia reukaufii, but not the bacterium Asaia astilbes. Volatile emissions differed significantly between microbial treatments and with nectar concentration, while sugar concentration was relatively similar among mono- and cocultures. Coculture volatile emission closely resembled an additive combination of monoculture volatiles. Despite differences in microbial growth and chemosensory cues, honey bee feeding did not differ between microbial monocultures and assemblages. Taken together, our results suggest that in some cases, chemical and ecological effects of microbial assemblages are largely predictable from those of component species, but caution that more work is necessary to predict under what circumstances non-additive effects are important.