Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.

Multicopper Oxidases and Oxygenases

The colonization of land by plants appears to have coincided with the appearance of mycorrhiza-like fungi. Over evolutionary time, fungi have maintained their prominent role in the formation of mycorrhizal associations. In addition, however, they have been able to occupy other terrestrial niches of which the decomposition of recalcitrant organic matter is perhaps the most remarkable. This implies that, in contrast to that of aquatic organic matter decomposition, bacteria have not been able to monopolize decomposition processes in terrestrial ecosystems. The emergence of fungi in terrestrial ecosystems must have had a strong impact on the evolution of terrestrial bacteria. On the one hand, potential decomposition niches, e.g. lignin degradation, have been lost for bacteria, whereas on the other hand the presence of fungi has itself created new bacterial niches. Confrontation between bacteria and fungi is ongoing, and from studying contemporary interactions, we can learn about the impact that fungi presently have, and have had in the past, on the ecology and evolution of terrestrial bacteria. In the first part of this review, the focus is on niche differentiation between soil bacteria and fungi involved in the decomposition of plant-derived organic matter. Bacteria and fungi are seen to compete for simple plant-derived substrates and have developed antagonistic strategies. For more recalcitrant organic substrates, e.g. cellulose and lignin, both competitive and mutualistic strategies appear to have evolved. In the second part of the review, bacterial niches with respect to the utilization of fungal-derived substrates are considered. Here, several lines of development can be recognized, ranging from mutualistic exudate-consuming bacteria that are associated with fungal surfaces to endosymbiotic and mycophagous bacteria. In some cases, there are indications of fungal specific selection in fungus-associated bacteria, and possible mechanisms for such selection are discussed.

Living in a fungal world: impact of fungi on soil bacterial niche development⋆

Lignocellulosic residues : Biodegradation and bioconversion by fungi

Chemical modification of lignins: Towards biobased polymers

White-rot fungi and their enzymes for the treatment of industrial dye effluents.

Biodegradation of lignin by white rot fungi.

The effect of fungal laccase on fractionated lignosulphonates (peritan Na)

The extracellular laccase of white rot fungus Cerrena unicolor was purified from culture by ion-exchange chromatography on DEAE-Toyopearl column and immobilized on silanized porous glass heads. During bonding procedure 94.35% protein and 100 % laccase activity were coupled to the support. Optimum pH for immobilized laccase compared to free enzyme was shifted from 5.5 to 5.7. The immobilized laccase was more resistant for thermal denaturation: at 70°C, the activity of immobilized enzyme was around 20 % higher than that of the free enzyme. It was also more stable during storage at 4°C. After about seven months the immobilized laccase retained 94.81 % of its initial activity, whereas free enzyme only 39.59 %. Nine water-miscible organic solvents tested in an anhydrous form caused an inhibitory effect on both laccase forms, but, in the mixture with water, the enzyme in all cases shows activity. It decreased, however, when the concentration of solvents increased. Among all solvents, the best results were obtained with ethylene glycol and methoxyethanol. When the reaction mixture contained 50 % of ethylene glycol, free and immobilized laccase retained 24 and 31 % respectively of their activity in the buffer. In the case of 50 % methoxyethanol these data were 6 and 36 %. Organic solvents shifted pH optima of both laccase forms to pH 6.0. The calculation from Lineweaver-Burk plot oxidizing capacity of laccase towards syringaldazine was slightly higher for the free enzyme than for immobilized one, 18.5 and 20.0 M/l respectively. These results show that Cerrena unicolor laccase both in free and immobilized form is able to catalyze the oxidation of syringaldazine in organic solvents. It may be usable in transformation of substrates insoluble or sparingly soluble in water. The immobilized laccase, as more stable and temperature resistant than free enzyme, seems to be more useful.

Activity of Free and Immobilized Extracellular Cerrena unicolor Laccase in Water Miscible Organic Solvents

Protocatechuate 3,4-dioxygenase (see protocatechuate: oxygen 3,4-oxidoreductase, EC 1.13.11.3) was isolated from the mycelium of Pleurotus ostreatus (induced with p-hydroxybenzoic acid) and immobilized on controlled porosity glass beads. Four fractions of Na–lignosulfonates (varying in Mr, after chromatography on Sephadex G-50) were treated with the immobilized enzyme. The products after incubation showed the same Mr as the untreated fractions, but their light absorption at 280 nm considerably decreased. These studies indicate that dioxygenase causes partial dearomatization of lignin macromolecule.

Dearomatization of lignin derivatives by fungal protocatechuate 3,4‐dioxygenase immobilized on porosity glass

In Pleurotus ostreatus protocatechuic acid is degraded by protocatechuate 3,4-dioxygenase (protocatechuate: oxygen 3,4-oxidoreductase, EC 1.13.11.3) via "intradiol" cleavage of aromatic ring to form beta-carboxy-cis,cis-muconic acid. The enzyme was isolated from the mycelium induced with p-hydroxybenzoic acid. An about 460-fold purification of the enzyme was achieved by ammonium sulphate fractionation, and DEAE-cellulose and Sephadex G-200 chromatography. The enzyme was homogeneous on analytical electrophoresis under non-denaturing conditions, whereas in the presence of sodium dodecyl sulphate several polypeptides of low molecular weight appeared additionally in trace amounts. Molecular weight of the enzyme, determined by gel filtration and electrophoresis was 200 000 and 205 000, respectively. The enzyme showed low substrate specificity, its pH optimum was 8.0 and Michaelis constant for protocatechuic acid was 14.2 microM.

Maria Wojtaś-Wasilewska

Papers

Biodegradation of lignin by white rot fungi.

The effect of fungal laccase on fractionated lignosulphonates (peritan Na)

Activity of Free and Immobilized Extracellular Cerrena unicolor Laccase in Water Miscible Organic Solvents

Dearomatization of lignin derivatives by fungal protocatechuate 3,4‐dioxygenase immobilized on porosity glass

Aromatic ring cleavage of protocatechuic acid by the white-rot fungus Pleurotus ostreatus.