Degradation of gallic acid and hydrolysable polyphenols is constitutively activated in the freshwater plant-associated bacterium Matsuebacter sp. FB25

Hydrolysable polyphenols are present in Myriophyllum spicatum L. at high concentrations of up to 25% of dry matter and are also excreted. Bacteria associated with the submerged macrophyte M. spicatum isolated from the surrounding water column and epiphytic biofilm were tested for their ability to degrade polyphenols. Several bacterial isolates were capable of growing with tannic acid as the sole carbon and energy source, among them Matsuebacter sp. FB25, Agrobacterium vitis EB26 and Pseudomonas sp. FB22. Cell suspensions of Matsuebacter sp. precultured on succinate were capable of degrading gallic acid, while those of A. vitis were not, indicating the constitutive presence of gallate-degrading enzymes in the former. When cells were precultured on gallic or tannic acid, cell suspensions of both strains exhibited an enhanced degradation rate of gallic acid. M. spicatum-derived hydrolysable polyphenols, which are comparable in structure to tannic acid, resulted in the same enhanced degradation rate of gallic acid or tellimagrandin II, the major M. spicatum polyphenol, by cell suspensions of Matsuebacter sp. FB25. The presence of polyphenoldegrading bacteria in the vicinity of M. spicatum explains the observed fast disappearance of tellimagrandin II and other hydrolysable polyphenols after excretion and has implications for allelochemical interference with competitors, herbivores and potential pathogenic microorganisms. The presence of Matsuebacter sp. and other polyphenol-degrading strains in such environments suggests a sufficiently strong effect of M. spicatum exudates to bring about selection in favour of highly specialised bacteria.