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We report here the first genome sequence of the white-rot fungus Obba rivulosa (Polyporales, Basidiomycota), a polypore known for its lignin-decomposing ability. The genome is based on the homokaryon 3A-2 originating in Finland. The genome is typical in size and carbohydrate active enzyme (CAZy) content for wood-decomposing basidiomycetes.

Oxatate decarboxylase (ODC) catalyses the conversion of oxalic acid to formic acid and C[O.sub.2] in bacteria and fungi. In wood-decaying fungi the enzyme has been linked to the regulation of intra-and extracellular quantities of oxalic acid, which is one of the key components in biological decomposition of wood. ODC enzymes are biotechnologically interesting for their potential in diagnostics, agriculture and environmental applications, e.g. removal of oxalic acid from industrial wastewaters. We identified a novel ODC in mycelial extracts of two wild-type isolates of Dichomitus squalens, and cloned the corresponding Ds-odc gene. The primary structure of the Ds-ODC protein contains two conserved Mn-binding cupin motifs, but at the N-terminus, a unique, approximately 60 aa alanine-serine-rich region is found. Real-time quantitative RT-PCR analysis confirmed gene expression when the fungus was cultivated on wood and in liquid medium. However, addition of oxalic acid in liquid cultures caused no increase in transcript amounts, thereby indicating a constitutive rather than inducible expression of Ds-odc. The detected stimulation of ODC activity by oxalic acid is more likely due to enzyme activation than to transcriptional upregulation of the Ds-odc gene. Our results support involvement of ODC in primary rather than secondary metabolism in fungi.

The basidiomycete isolate b19, originally identified by morphological characteristics of the fruiting body as Nematoloma frowardii, efficiently produces manganese peroxidase (MNP) and is used for degradation of natural, persistent aromatic polymers (lignin, humic acids and brown coal components). The N. frowardii MNP has shown good activity in conversion of xenobiotic compounds such as polycyclic hydrocarbons and trinitrotoluene. However, this biotechnologically promising fungus has not previously been studied at the molecular biology level. We show here that according to the molecular characterization of its main MNP isozyme, Nf b19 MNP2, and partial sequencing of its MNP3-, three lignin peroxidase- and two laccase-encoding genes, and the gene encoding the ribosomal SSU 18S RNA, that the fungus has a close phylogenetic relationship to the white-rot basidiomycete Phlebia radiata (Fr.). Ribosomal internal transcribed spacer (ITS) sequence (ITS1 +5.8S+ITS2) phylogeny reclassifies Nf b19 as a possible representative of a new species of the genus Phlebia, nearest to the Phlebia acerina clade. The genus Phlebia belongs to a completely different family (Corticiaceae) and order (Aphyllophorales) within the phylum Basidiomycota than the genus Nematoloma, which is classified in the order Agaricales, family Strophariaceae. Our results thus indicate a need for systematic re-identification of the previously named N. frowardii isolate b19.

Researchers demonstrate for the first time the biodegradation of lignin in solid pine wood by manganese peroxidase from the white-rot fungus Phlebia radiata. In this system, a nonphenolic lignin structure that is not normally degraded by manganese peroxidase was oxidizable.

Manganese peroxidase (MnP) is the predominant ligninolytic enzyme during solid-state fermentation (SSF) of wheat straw with the white rot fungus Nematoloma frowardii. The fungus generates sufficient amounts of organic acids for effective MnP activity. Aside from MnP, low levels of laccase and lignin peroxidase were also detected during SSF. Synthetic 14C-ring labeled lignin was degraded during SSF. About 75% of the initial radioactivity was released as (super 14)CO(sub 2), while only 6% was associated with the residual straw material, thus leading to the conclusion that at least partial extracellular mineralization of lignin may have taken place.