COS 57-4 - Where the bee suck, there suck the yeast; diffuse mutualisms between diverse nectar yeasts and bumble bee pollinators

Background/Question/Methods

Despite the importance of yeast in human endeavors, the ecology of wild yeasts is poorly understood. Nectar yeasts and insect pollinators may be involved in a complex system of diffuse mutualisms, which are a poorly understood part of pollination ecology. Nectar yeasts are often treated homogeneously or considered simply as part of a broader nectar microbiome. However, nectar yeasts are taxonomically and physiologically diverse, spanning taxa that are separated by hundreds of millions of years. Here, we take a yeast-centric approach, and ask whether nectar yeast species differ in their attractiveness to bee pollinators.

Building on a collection of insect-associated nectar yeasts gathered over seven years, we compared the responses of bumble bees to different nectar yeast species with two-choice preference trials. Using six nectar yeast species spanning three genera, we analyzed the frequency and duration of bumble bee visits to artificial nectar with and without inoculated yeast. To investigate the genetic and physiological pathways that underpin nectar yeast-insect relationships, we examined the role of a volatile producing gene, ATF1, in attracting bumble bee pollinators. To do this, we cloned ATF1 homologs from nectar yeast into a knock-out strain of the model yeast species Saccharomyces cerevisiae and assayed bumblebee preference.

Results/Conclusions

Our preliminary results suggest that the bumble bee Bombus impatiens readily foraged on artificial nectar with low concentrations of nectar yeast (~1000 cells/µl). For the most well-studied nectar yeast species, Metschnikowia reukaufii, bumble bees that fed from both nectar treatments foraged more frequently on nectar inoculated with yeast than nectar without yeast. Bumblebees that foraged on only one treatment did so randomly between nectar with and without yeast, and spent a longer time foraging than bees that visited both treatments. These results indicate that bees show a preference for artificial nectar inoculated with M. reukaufii, but only when they have foraged on nectar without yeast as well.

In S. cerevisiae, the ATF1 gene is known to play a key role in attracting fruit flies. We aimed to clone homologs from nectar yeast species into ATF1 knock out strains of S. cerevisiae to determine if the gene serves a similar function to attract insect pollinators. Our preliminary results show that the ATF1 homolog from the nectar yeast Lachancea fermentati can be transformed into pIL7 plasmids and uptaken by E. coli. Further work is needed to successfully clone the L. fermentati ATF1 homolog into S. cerevisiae, and assay bumble bee attraction