Pisolithus arrhizus: insights toward its life in a geothermal environment

The ectomycorrhizal fungus genus Pisolithus is only found in two geothermal areas on Earth: New Zealand and Norris Geyser Basing (NGB), Yellowstone National Park (YNP). In NGB, YNP Pisolithus arrhizus (Scop.) Rauschert is growing without apparent mycorrhizal associations. This study provides some of the first insights into the life of P. arrhizus in a geothermal area. Nine genera of bacteria associated with the fruiting body of P. arrhizus were cultured and identified using the 16S rRNA gene: Bacillus, Brevibacillus, Brevibacterium, Clostridium, Desulfotomaculum, Geobacillus, Nocardia, Paenibacillus, and Serratia. Further insight into the life of P. arrhizus in NGB, YNP is provide through enzyme assays. A total of fifteen different enzymes involved in different energy pathways were assayed for activity. P. arrhizus proved challenging to work with, and yielded inconclusive results for most enzymes. Sulfite oxidase proved a model example of inconclusive results, while glucose-6-phosphate dehydrogenase and polyphenol oxidase (PPO) were both present. The PPO from P. arrhizus in NGB was active on every diphenol tested: catechol, 4-methylcatechol, L-DOPA and cholorgenic acid. Further, the PPO cannot be classified as a tyrosinase because no cresolase (monophenolase) activity was observed on tyrosine. Additionally, the PPO has a working pH range of ≤ 5.1 to ≥ 8.6.