The presence of "Paxillus involutus" is related to much reduced numbers of bacteria associated with the roots of "Pinus sylvestris". Instead bacteria are found on the external mycelium. The types of bacteria change as well; a Finnish study published in 1997 found that bacterial communities under "P. sylvestris" without mycorrhizae metabolised organic and amino acids, while communities among "P. involutus" metabolised the sugar fructose. "Paxillus involutus" benefits from the presence of some species of bacteria in the soil it grows in. As the fungus grows it excretes polyphenols, waste products that are toxic to itself and impede its growth, but these compounds are metabolised by some bacteria, resulting in increased fungal growth. Bacteria also produce certain compounds such as citric and malic acid, which stimulate "P. involutus".