Degradation of Humic Acids by the Litter-Decomposing Basidiomycete Collybia dryophila

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American Society for Microbiology

RESUMO

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 14C-labeled humic acid (14C-HA) prepared from [U-14C]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 Mn2+ (200 μM), leading to 75% conversion of LHA and 50% mineralization of 14C-HA (compared to 60% and 20%, respectively, in the absence of Mn2+). There was a strong indication that manganese peroxidase (MnP), the production of which was noticeably increased in Mn2+-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.

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