Bacteria associated with flowers affect the reproductive success of Brassica napus L. via scent-mediated interactions with pollinators

Flowers are colonized by specific bacterial communities that have been shown to affect floral scent emission and pollinator behavior. Whether these effects translate into changes in the plants reproductive success remains unknown. In our study, flowers of Brassica napus were inoculated with the phyllospheric bacteria Pantoea agglomerans and Pseudomonas syringae. Next-generation 16S rRNA gene amplicon sequencing of bacterial communities associated with flowers showed that inoculation was efficient and affected bacterial communities throughout the flowering time of individual flowers. Flowers of B. napus inoculated with P. agglomerans and P. syringae were preferred by pollinators in the field or in olfactometer assays. Presumably due to the increased visitation rates, inoculated plants produced more seeds of tendentially higher quality per flower. Floral scent emissions were affected by time after inoculation and by treatment with bacterial strains, potentially explaining the behavioral responses of pollinators. Controlled laboratory experiments showed that bacteria emit volatiles through their own metabolism and that the concentrations of some floral volatiles can be reduced by bacteria. Furthermore, our results also suggest that bacteria can use floral scent compounds as carbon sources. Our results demonstrate a significant effect of floral bacteria on the pollination and reproduction of entomophilous plants that is at least partly mediated by their effects on floral chemical signaling.