These compounds are typically found from wounded plants, and as a result VirA is used by "Agrobacterium tumefaciens" to locate potential host organisms for infection. Natural phenols can be involved in allelopathic interactions, for example in soil or in water. Juglone is an example of such a molecule inhibiting the growth of other plant species around walnut trees. The aquatic vascular plant "Myriophyllum spicatum" produces ellagic, gallic and pyrogallic acids and (+)-catechin, allelopathic phenolic compounds inhibiting the growth of blue-green alga "Microcystis aeruginosa". Phenolics, and in particular flavonoids and isoflavonoids, may be involved in endomycorrhizae formation. Acetosyringone has been best known for its involvement in plant-pathogen recognition, especially its role as a signal attracting and transforming unique, oncogenic bacteria in genus "Agrobacterium". The virA gene on the Ti plasmid in the genome of "Agrobacterium tumefaciens" and "Agrobacterium rhizogenes" is used by these soil bacteria to infect plants, via its encoding for a receptor for acetosyringone and other phenolic phytochemicals exuded by plant wounds. This compound also allows higher transformation efficiency in plants, in A. tumefaciens mediated transformation procedures, and so is of importance in plant biotechnology. Notable sources of natural phenols in human nutrition include berries, tea, beer, olive oil, chocolate or cocoa, coffee, pomegranates, popcorn, yerba maté, fruits and fruit based drinks (including cider, wine and vinegar) and vegetables. Herbs and spices, nuts (walnuts, peanut) and algae are also potentially significant for supplying certain natural phenols. Natural phenols can also be found in fatty matrices like olive oil. Unfiltered olive oil has the higher levels of phenols, or polar phenols that form a complex phenol-protein complex. Phenolic compounds, when used in beverages, such as prune juice, have been shown to be helpful in the color and sensory components, such as alleviating bitterness. Some advocates for organic farming claim that organically grown potatoes, oranges, and leaf vegetables have more phenolic compounds and these may provide antioxidant protection against heart disease and cancer. However evidence on substantial differences between organic food and conventional food is insufficient to make claims that organic food is safer or more healthy than conventional food.