Nectar microbes can reduce secondary metabolites in nectar and alter effects on nectar consumption by pollinators

Abstract

Secondary metabolites that are present in floral nectar have been hypothesized to enhance specificity in plant-pollinator mutualism by reducing larceny by non-pollinators, including microorganisms that colonize nectar. However, few studies have tested this hypothesis. Using synthetic nectar, we conducted Accepted ArticleThis article is protected by copyright. All rights reserved. laboratory and field experiments to examine the effects of five chemical compounds found in nectar on the growth and metabolism of nectar-colonizing yeasts and bacteria, and the interactive effects of these compounds and nectar microbes on the consumption of nectar by pollinators. In most cases, focal compounds inhibited microbial growth, but the extent of these effects depended on compound identity, concentration, and microbial species. Moreover, most compounds did not substantially decrease sugar metabolism by microbes, and microbes reduced the concentration of some compounds in nectar. Using artificial flowers in the field, we also found that the common nectar yeast Metschnikowia reukaufii altered nectar consumption by small floral visitors, but only in nectar containing catalpol. This effect was likely mediated by a mechanism independent of catalpol metabolism. Despite strong compound-specific effects on microbial growth, our results suggest that the secondary metabolites tested here are unlikely to be an effective general defense mechanism for preserving nectar sugars for pollinators. Instead, our results indicate that microbial colonization of nectar could reduce the concentration of secondary compounds in nectar and, in some cases, reduce deterrence to pollinators.

Genomic diversity of a nectar yeast clusters into metabolically, but not geographically, distinct lineages

“…Finally, we should also note that nectar‐colonizing microbes, both yeast and bacteria, can rapidly and markedly change the chemical composition in varied ways (Vannette & Fukami, , ; Vannette, Gauthier, & Fukami, ). Nectar modification by microbes can influence pollinator visitation (Vannette et al., ), and our preliminary observations suggest that yeasts are more reliant on pollinators than bacteria, leading to unequal influence of nectar modification on their dispersal history.…”

Specialist nectar-yeasts decline with urbanization in Berlin

“…Those plant species-specific differences could be caused by variation in sugar content or other chemical properties of the nectar, e.g. content of secondary metabolites or amino acids2627. Next to these chemical factors, differences in pollinator identity, their visitation rates, and abundance could have led to the distinct local yeast distribution in nectar of both plant species9 due to differences in flower morphology or flowering time28.…”

Floral Metabolism of Sugars and Amino Acids: Implications for Pollinators’ Preferences and Seed and Fruit Set

“…Similarly to yeast, bacterial growth also correlates negatively with total sugar content and/or Suc content in nectar but usually correlates positively with the proportion of the monosaccharide Fru (Vannette et al, 2012;Lenaerts et al, 2016;Vannette and Fukami, 2016). In addition, bacterial isolates of the genus Acinetobacter can convert Suc into a mucous matrix of polysaccharides (Fridman et al, 2012;Fig.…”