Tamara Vares

Oxidative decomposition of malonic acid as basis for the action of manganese peroxidase in the absence of hydrogen peroxide

Manganese peroxidase (MnP) from the ligninolytic basidiomycetes Phlebia radiata and Nematoloma frowardii was found to decompose malonate oxidatively in the absence of H2O2 in a reaction system consisting of the enzyme, sodium malonate and MnCl2. The enzymatic oxidation resulted in a substantial decrease in malonate concentration and the formation of CO2, oxalate, glyoxylate and formate. Simultaneously with the decomposition of malonate, Mn(II) was oxidized to Mn(III) leading to high transient concentrations of the latter. MnP action in the absence of H2O2 started slowly after a lag period of 3 h. The lag period was considerably shortened after a single addition of Mn(III). Superoxide dismutase and catalase inhibited the enzymatic reaction partly, ascorbate completely. ESR studies demonstrated the formation of a carbon‐centered radical during the course of the reaction. We propose that the latter generates peroxides that can be used by MnP to oxidize Mn(II) to Mn(III).

Production of organic acids by different white-rot fungi as detected using capillary zone electrophoresis

Capillary zone electrophoresis was used as an analytical method for the first time to determine organic acids accumulated by 15 white-rot fungi both in liquid and solid lignocellulose medium. Oxalic acid accumulation by Phanerochaete chrysosporium F1767 (ATCC 24725), Phlebia radiata 79 (ATCC 64658) and Ceriporiopsis sub-vermispora FP-90031-sp in the solid medium was maximal during the first and second weeks of growth.

Transformation of wheat straw in the course of solid-state fermentation by four ligninolytic basidiomycetes

Biological upgrading of wheat straw by the white-rot fungi Phanerochaete chrysosporium , Pleurotus eryngii, Phlebia radiata, and Ceriporiopsis subvermisporawas monitored during 60-day solid-state fermentation. Analysis of straw included determination of weight loss and lignin content, color analysis, and infrared spectroscopy, whereas the studies on the water-soluble fractions were carried out by infrared spectroscopy, elementary analyses and quantification of the total phenols and reducing sugars. The most selective degradation of lignin was produced by P. eryngii and especially by C. subvermispora, the former species releasing the greatest amount of colored water-soluble products, whereas an increase in straw brightness was caused by C. subvermispora.In general, the composition of the water-soluble fraction correlated with the extent of straw transformation. The initial fermentation stage (0 ‐15 days) was characterized by the accumulation of water-soluble products from lignin degradation and fungal metabolism, the concentration of which tended to stabilize in the second stage (16 ‐ 60 days). The degree of delignification at the second stage tended to coincide with the decrease of the water-soluble nitrogen.

Manganese and malonate are individual regulators for the production of lignin and manganese peroxidase isozymes and in the degradation of lignin by Phlebia radiata

Abstract The effects of high manganese [180 μM Mn(II)] concentration and addition of malonate (10 mM) were studied in nitrogen-limited cultures of the white-rot fungus, Phlebia radiata. High levels of manganese alone showed no systematic influence on the production of lignin peroxidase (LiP), manganese peroxidase (MnP) or laccase. In contrast, high-manganese containing cultures of P. radiata showed lower efficiency in the mineralization of 14C-ring-labelled synthetic lignin ([14C]DHP). The highest rates of mineralization, up to 30% in 18 days, were reached in low- manganese(2 μM)-containing cultures when malonate was omitted. Degradation of [14C]DHP was substantially restricted by the addition of malonate. The combination of high manganese and malonate resulted in increased levels of MnP and laccase production, whereas LiP production was repressed. Also, the profiles of expression of the MnP and LiP isozymes were affected. A new P. radiata MnP isozyme of pI 3.6 (MnP3) was found in the high-manganese cultures. Addition of malonate alone caused some repression but also stimulating effects on distinctive MnP and LiP isozymes. The results indicate that manganese and malonate are individual regulators of MnP and LiP expression and have different roles in the degradation of lignin by P. radiata.

Production of multiple lignin peroxidases by the white-rot fungus Phlebia ochraceofulva

Abstract The white-rot fungus Phlebiaochraceofulva (Bourd. & Galz.) Donk. strain 75144 actively produced lignin peroxidase (LiP) under nitrogen-limited cultivation conditions. Maximal activity was reached during days 6–8 of growth in bioreactors containing immobilized mycelium and either a low basal concentration of Mn(II) (0.12 ppm) or a 10-fold concentration of Mn(II) (1.2 ppm). Laccase activity was also detected in the extracellular fluid of P. ochraceofulva, but no Mn-peroxidase (MnP) activity was observed with either level of Mn(II). Five lignin peroxidases were purified and partially characterized.