Quantitative assessment of nectar microbe-produced volatiles

Authors: Rering, Caitlin; Beck, John; VANNETTE, RACHEL - University Of California, Davis; Willms, Steve

Submitted to: ACS Symposium Series
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2018
Publication Date: 8/28/2018
Citation: Rering, C.C., Beck, J.J., Vannette, R.L., Willms, S.D. 2018. Quantitative assessment of nectar microbe-produced volatiles. ACS Symposium Series. 1294:127-142. https://doi.org/10.1021/bk-2018-1294.ch010.
DOI: https://doi.org/10.1021/bk-2018-1294.ch010

Interpretive Summary: Plants and their flowers can be host to a range of microbes (i.e., fungi and bacteria). The microbes that reside in the nectar can consume its components (i.e., sugar and amino acids), and as a result emit odors of their own. The presence and emission of these microbes may have significant impacts on attracting or inhibiting pollinators (i.e., bees), as well as consequences for plant reproduction. This complex web of interactions among the nectar, microbes and pollinator present multifaceted challenges to investigations of their chemical communication. Here, Scientists from the ARS Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, in collaboration with a scientist from University of California, Davis, Department of Entomology and Nematology, provide an overview of the current understanding of floral nectar production, chemistry and microbiology. We then explore known ecological interactions between plants, microbes and floral visitors and advocate for continued consideration of floral microbes in pollination ecology studies. A discussion of challenges pertaining to microbial community assessment and odor detection in the field is offered and approaches adopted in the literature are critically compared. Finally, an environmental fate conceptual model is applied to microbial odor emission from nectar. Unanswered questions remain before nectar microbe-produced odors can be accurately described by fate modelling. However, the coupling of floral odor plume dynamic modeling with biogeographical models of species distribution could prove a powerful tool for further exploration of these important nectar-microbe-pollinator interactions. Detailed studies of these interactions can lead to a better understanding of the microbe-nectar emissions and the possible manipulation of this relationship for healthier or more productive flower-pollinator interactions.

Technical Abstract: Nectar microbe-produced volatiles can contribute to floral blends and modify pollinator preference for flowers. Identifying and describing the compounds that may underlie this effect is a key goal. Semi-quantitative or quantitative data is often critical for chemical ecology investigations, given that biotic responses (i.e., insects or plants) can fluctuate with concentration, relative ratios, or composition of the emitted volatile profiles. However, field-based, in situ microbial volatile detection and quantification is difficult due to the small scale of the nectar microhabitat. Laboratory-based inoculations of bulk synthetic nectars are useful for screening weakly-abundant and difficult to analyze volatiles, which may be crucial in eliciting responses. Despite the limitations of this approach, it allows rapid identification of target molecules for further validation with bioassays. Targeted analytical methods to identify or quantify semiochemicals may then be developed and validated for field tests. Here, we report the first quantitative assessment of microbe volatile emission in laboratory-based tests with synthetic nectar. We also review briefly solid phase microextraction collection and gas-chromatography data interpretation. Nectar microbe interactions with plants and insects offer opportunities for agricultural improvement, and a selection of potential uses are highlighted.