Interkingdom transfer of the human pathogen Propionibacterium acnes to the plant endosphere, and its adaptation

Humans, like most organisms, have established a long-lasting cohabitation with a variety of microbes, including pathogens and gut-associated bacteria. Studies investigating such associations documented numerous cases of bacterial host switches (usually from domestic animals to humans). Much less is known about the exchange of microbial symbionts between humans and plants. We report a surprising and, to our knowledge, unique example of horizontal interkingdom transfer of a human opportunistic pathogen (Propionibacterium acnes) to a crop plant (the domesticated grapevine Vitis vinifera L.). P. acnes was localised in the bark, in xylem fibers, and, more interestingly, inside pith tissues, by fluorescent in-situ hybridization (FISH). Phylogenetic and population genetic analyses indicate that the establishment of the grapevine-associated P. acnes as obligate endophyte is compatible with a recent transfer event, likely during the Neolithic, when grapevine was domesticated.