Increased endoplasmic reticulum content of Phanerochaete chrysosporium INA-12 by inositol phospholipid precursor in relation to peroxidase excretion

Regulation of fungal decomposition at single-cell level

Filamentous fungi play a key role as decomposers in Earth's nutrient cycles. In soils, substrates are heterogeneously distributed in microenvironments. Hence, individual hyphae of a mycelium may experience very different environmental conditions simultaneously. In the current work, we investigated how fungi cope with local environmental variations at single-cell level. We developed a method based on infrared spectroscopy that allows the direct, in-situ chemical imaging of the decomposition activity of individual hyphal tips. Colonies of the ectomycorrhizal Basidiomycete Paxillus involutus were grown on liquid media, while parts of colonies were allowed to colonize lignin patches. Oxidative decomposition of lignin by individual hyphae growing under different conditions was followed for a period of seven days. We identified two sub-populations of hyphal tips: one with low decomposition activity and one with much higher activity. Active cells secreted more extracellular polymeric substances and oxidized lignin more strongly. The ratio of active to inactive hyphae strongly depended on the environmental conditions in lignin patches, but was further mediated by the decomposition activity of entire mycelia. Phenotypic heterogeneity occurring between genetically identical hyphal tips may be an important strategy for filamentous fungi to cope with heterogeneous and constantly changing soil environments.

Comparison of static and agitated immobilized cultures of Phanerochaete chrysosporium for the degradation of pentachlorophenol and its metabolite pentachloroanisole

The transformation of pentachlorophenol (PCP) by Phanerochaete chrysosporium I-1512 in relation to pentachloroanisole (PCA) was studied in two different modes of culture. The degradation of PCP by immobilized cells in agitated medium was compared with that by static cultures. Results clearly established the advantage of an immobilized culture for mineralization of PCP: 23% of CO2 released for fungus immobilized on stainless steel mesh rings as compared with 11% for static cultures. PCA, a metabolite of PCP, was formed only in static cultures and underwent a limited mineralization. Moreover, experiments performed with mycelium and culture supernatant (in the presence of cycloheximide) clearly demonstrated that PCA formation was catalyzed by the biomass in static cultures of P. chrysosporium. Assays in vitro did not establish any involvement of lignin or manganese peroxidases in PCP or PCA transformation.Key words: filamentous fungi, Phanerochaete chrysosporium, pentachlorophenol, pentachloroanisole.

Production of Phanerochaete chrysosporium lignin peroxidase

Liginin peroxidase (ligninase) of the white rot fungus Phanerochaete chrysosporium Burdsall was discovered in 1982 as a secondary metabolite. Today multiple isoenzymes are known, which are often collectively called as lignin peroxidase. Lignin peroxidase has been characterized as a veratryl alcohol oxidizing enzyme, but it is a relatively unspecific enzyme catalyzing a variety of reactions with hydrogen peroxide as the electron acceptor. P. chrysosporium ligninases are heme glycoproteins. At least a number of isoenzymes are also phosphorylated. Two of the major isoenzymes have been crystallized. Until recently lignin peroxidase could only be produced in low yields in very small scale stationary cultures owing to shear sensitivity. Most strains produce the enzyme only after grown under nitrogen or carbon limitation, although strains producing lignin peroxidase under nutrient sufficiency have also been isolated. Activities over 2000 U dm(-3) (as determined at 30 degrees to 37 degrees C) have been reported in small scale Erlenmeyer cultures with the strain INA-12 grown on glycerol in the presence of soybean phospholipids under nitrogen sufficiency. In about 8 dm(3) liquid volume pilot scale higher than 100 U dm(-3) (as determined at 23 degrees C) have been obtained under agitation with immobilized P. chrysosporium strains ATCC 24725 or TKK 20512. Good results have been obtained for example with nylon web, polyurethane foam, sintered glass or silicon tubing as the carrier. The immobilized biocatalyst systems have also made large scale repeated batch and semicontinuous production possible. With nylon web as the carrier, lignin peroxidase production has recently been scaled up to 800 dm(3) liquid volume semicontinuous industrial production process.