White-rot Fungus Phanerochaete Sordida YK-624 Research Articles

Intracellular ferrireductase involved in Mn(IV)-reducing enzyme system to supply Mn(II) for lignin biodegradation by white-rot fungus Phanerochaete sordida YK-624

In the biobleaching of kraft pulp with white-rot fungus Phanerochaete sordida YK-624, it was confirmed that manganese dioxide (Mn(IV)) in kraft pulp was reduced to Mn(II) by ESR analysis. By this reaction, the production of manganese peroxidase (MnP) by P. sordida YK-624 was triggered and then the kraft pulp was bleached with MnP. In the liquid culture, the reduction of manganese dioxide was observed by the washed mycelia of P. sordida YK-624 although smaller amount of Mn(II) was produced by the extracellular culture fluid. The reduction by the washed mycelia was dependent on Fe(II), a metal chelator, and NAD(P)H. Moreover, the cell-free extract from P. sordida YK-624 catalyzed the reduction of ferric chelate to ferrous chelate in the presence of NAD(P)H. It is likely, therefore, that ferrous chelate reduces manganese dioxide and that the produced ferric chelate is reduced by intracellular NAD(P)H-dependent reductase to regenerate ferrous chelate. An intracellular NADPH-dependent reductase, namely NADPH-dependent ferrireductase (molecular weight 35 kDa, pI 5.1), was purified from P. sordida YK-624. Moreover, there was a good correlation between the production of intracellular ferrireductase and that of extracellular MnP in a liquid culture containing manganese dioxide. These results suggest that the ferrireductase is involved in the production of MnP by the reduction of manganese dioxide to Mn(II).

Iron-binding compounds produced by white-rot fungusPhanerochaete sordida YK-624

Iron-binding compounds were isolated from a culture ofPhanerochaete sordida YK-624 and were found to bind to Fe(III) preferentially compared with Fe(II). Two iron-binding compounds were purified to near-homogeneity with gel permeation chromatography. Hydrolysis of the iron-binding compounds with 6N hydrochloric acid gave ninhydrin-negative products. The molecular weight of these compounds was 3–5 kDa. These compounds may play an important role in the reduction of extracellular manganese dioxide to Mn(II) by intracellular ferrireductases for lignin degradation by manganese peroxidase.

Change in oxidation state of manganese atoms in kraft pulp during biological bleaching with white-rot fungusPhanerochaete sordida YK-624

Change in the oxidation state of manganese atoms in unbleached hardwood kraft pulp (UKP) during the biological bleaching of UKP withPhanerochaete sordida YK-624 was determined by the electron spin resonance (ESR) method. The spectrum of Mn(II), which reveals hyperfine splitting, was not observed in the ESR analysis of UKP, but the spectrum for manganese dioxide was observed. After fungal treatment of UKP withP. sordida YK-624, the spectrum of Mn(II) was detected. The reduction of manganese dioxide was triggered by the increase in NADPH-dependent ferrireductase activity. It is concluded that the manganese dioxide dominant in UKP was reduced byP. sordida YK-624 to Mn(II), which stimulates the production and function of manganese peroxidase.

NADPH-dependent ferrireductase produced by white-rot fungusPhanerochaete sordida YK-624

An intracellular, soluble ferrireductase thought to be involved in the reduction of manganese dioxide by white-rot fungusPhanerochaete sordida YK-624 was purified for the first time. Two isoenzymes, NAD(P)H-dependent and NADPH-dependent, respectively, were detected by hydrophobic chromatography. The NADPH-dependent ferrireductase was purified to homogeneity by ammonium sulfate fractionation, hydrophobic interaction, gel permeation, and anion-exchange chromatography. The purified protein, which is monomeric, has a molecular mass of 35 kDa (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and pl 5.1 (determined by isoelectric focusing). The purified protein did not use cellobiose as an electron donor. The purified protein reduced Fe(III)-nitrilotriacetate complex, Mn(III)-malonate complex, methoxy-p-benzoquinone, and cytochrome c; veratraldehyde, 2-hydroxy-1,4-naphthoquinone, phenazine methosulfate, and plumbagin could not be reduced. Particularly, the protein showed the highest reducing rate for Fe(III)-organic acid complexes, such as Fe(III)-nitrilotriacetate, among these electron acceptors.