title: Degradation of humic acids by the litter-decomposing basidiomycete Collybia dryophila.
abstract: The basidiomycete Collybia dryophila K209, which colonizes forest soil, was found to decompose a natural humic acid isolated from pine-forest litter (LHA) and a synthetic (14)C-labeled humic acid ((14)C-HA) prepared from [U-(14)C]catechol in liquid culture. Degradation resulted in the formation of polar, lower-molecular-mass fulvic acid (FA) and carbon dioxide. HA decomposition was considerably enhanced in the presence of Mn(2+) (200 microM), leading to 75% conversion of LHA and 50% mineralization of (14)C-HA (compared to 60% and 20%, respectively, in the absence of Mn(2+)). There was a strong indication that manganese peroxidase (MnP), the production of which was noticeably increased in Mn(2+)-supplemented cultures, was responsible for this effect. The enzyme was produced as a single protein with a pI of 4.7 and a molecular mass of 44 kDa. During solid-state cultivation, C. dryophila released substantial amounts of water-soluble FA (predominantly of 0.9 kDa molecular mass) from insoluble litter material. The results indicate that basidiomycetes such as C. dryophila which colonize forest litter and soil are involved in humus turnover by their recycling of high-molecular-mass humic substances. Extracellular MnP seems to be a key enzyme in the conversion process.
authors.affiliation: Department of Applied Chemistry and Microbiology, Division of Microbiology, 00014 University of Helsinki, PO Box 56, Biocenter 1, Viikinkaari 9, FIN-00014 Helsinki, Finland. kari.steffen@helsinki.fi
authors.forename: Kari Timo
authors.initials: KT
authors.lastname: Steffen
authors.forename: Annele
authors.initials: A
authors.lastname: Hatakka
authors.forename: Martin
authors.initials: M
authors.lastname: Hofrichter
mesh_terms: D001487:Basidiomycota / Q000378:metabolism* / Q000502:physiology; D002250:Carbon Radioisotopes; D006812:Humic Substances / Q000378:metabolism*; D010544:Peroxidases / Q000302:isolation & purification / Q000378:metabolism; D028223:Pinus / Q000737:chemistry* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D006812:Humic Substances; D010544:Peroxidases; C051129:manganese peroxidase