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Dryad

Nectar bacteria stimulate pollen germination and bursting to enhance microbial fitness

Christensen, Shawn1

Published Jul 27, 2021 on Dryad. https://doi.org/10.25338/B8BS75

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Abstract

Many organisms consume pollen, yet mechanisms of its digestion remains a fundamental enigma in pollination biology, as pollen is protected by a recalcitrant outer shell. Pollen is commonly found in floral nectar, as are nectar microbes, which are nearly ubiquitous among flowers. Nectar specialist bacteria, like Acinetobacter, can reach high densities (up to 109 cells/mL), despite the fact that floral nectar is nitrogen poor. Here, we show evidence that the genus Acinetobacter, a prevalent nectar- and bee-associated bacteria, can induce pollen germination and bursting, gain access to protoplasm nutrients, and thereby grow to higher densities. Although induced germination has been suggested as a potential method in macroscopic pollen consumers, and fungal inhibition of pollen germination has been shown, direct biological induction of germination has not been empirically documented outside of plants. Acinetobacter pollinis SCC477 induced over 5x greater pollen germination and 20x greater pollen bursting than that of uninoculated pollen by 45 minutes. When provided with germinable pollen, A. pollinis stimulates protein release and grows to nearly twice the density compared to growth with ungerminable pollen, indicating that stimulation of germination benefits bacterial fitness. In contrast, a common nectar-inhabiting yeast did not affect pollen germination nor benefit from it. We conclude that Acinetobacter both specifically causes and benefits from inducing pollen germination and bursting. Further study of microbe-pollen interactions may inform many aspects of pollination ecology, including floral microbial ecology, pollinator nutrient acquisition from pollen, and cues of pollen germination for plant reproduction.