Mangroves are trees that grow in saline habitats in the tropics and subtropics. Plants in mangrove forests have developed a set of physiological adaptations in response to frequent tidal inundation. Mangroves and sea grasses provide a natural habitat for marine fungi. Marine fungi are often found on decayed lignocellulosic substrates such as prop roots, pneumatophores, branches, leaves, and driftwood in the intertidal region of mangrove stands. They are thought to play an important role in lignocellulosic degradation in such marine ecosystems (9). Commonly isolated marine fungi belong to ascomycetes and deuteromycetes, while basidiomycetes are relatively rarely reported (22,27,36). The lignocellulolytic enzymes of marine fungi have potential industrial and environmental applications (22,27,29).White rot fungi have a unique ability to decompose wood lignin via the secretion of extracellular lignin-degrading enzymes such as manganese peroxidase (MnP), lignin peroxidase, versatile peroxidase, and laccase. MnP is considered to be one of the key enzymes involved in lignin degradation caused by white rot fungi. MnP oxidizes Mn 2ϩ to Mn 3ϩ in an H 2 O 2 -dependent reaction, and Mn 3ϩ organic acid chelates oxidize monomeric phenol, phenolic lignin dimers, and synthetic lignin via the formation of a phenoxy radical (7,19). Additionally, MnP participates in lignin biodegradation via thiol and lipidderived free radicals that are able to oxidize a variety of nonphenolic aromatic compounds (1, 35). Although many genes encoding MnP have been cloned from several white rot fungi, there has been no report focusing on marine fungi.The marine fungus Phlebia sp. strain MG-60 was selected from 28 mushrooms and driftwoods collected from mangrove stands in Okinawa, Japan, based on PolyR-478 decolorization and lignin biodegradation under hypersaline conditions (15). Phlebia sp. strain MG-60 produces MnP mainly under hypersaline conditions. It was able to brighten the unbleached hardwood kraft pulp extensively even under conditions of 5% (wt/ vol) sea salts. In contrast, pulp was only slightly brightened by the widely studied white rot fungus Phanerochaete chrysosporium at 3% (wt/vol) and 5% (wt/vol) sea salt concentrations (15, 16). Thus, MG-60 has significant bleaching ability, especially in a hypersaline environment.To clarify the effect of hypersaline conditions on MnP production from Phlebia sp. strain MG-60, herein, we compare the productions of MnP activity and different MnP isozymes under normal and hypersaline conditions. We also provide the full sequences of three new MnP-encoding genes, MGmnp1, MGmnp2, and MGmnp3, which are differentially regulated in response to saline stress. MATERIALS AND METHODSFungal cultures. Phlebia sp. strain MG-60 TUFC40001 (Fungus/Mushroom Resource and Research Center, Tottori, Japan), Trametes versicolor NBRC6482, and Phanerochaete chrysosporium ATCC 34541 were maintained on potato dextrose agar (PDA) plates. Mycelium mats on an agar plate were transferred into a sterilized blender cup containing 5...
Bioremediation is a low-cost treatment alternative for the cleanup of polychlorinated-dioxin-contaminated soils and fly ash when pollution spread is wide-ranging. An interesting fungus, Ceriporia sp. MZ-340, with a high ability to degrade dioxin, was isolated from white rotten wood of a broadleaf tree from Kyushu Island in Japan. We have attempted to use the fungus for bioremediation of polychlorinated-dioxin-contaminated soil on site. However, we have to consider that this trial has the potential problem of introducing a biohazard to a natural ecosystem if this organism is naturalized. We have therefore developed a monitoring system for the introduced fungus as a part of the examination and evaluation of bioremediation in our laboratory. We have also developed a PCR-based assay to reliably detect the fungus at the bioremediation site. DNA isolated from the site was amplified by PCR using a specific primer derived from internal transcribed spacer region (ITS: ITS1, 5.8S rDNA and ITS2) sequences of Ceriporia sp. MZ-340. We successfully monitored Ceriporia sp. MZ-340 down to 100 fg/ micro l DNA and down to 2 mg/g mycelium. We also successfully monitored the fungus specifically at the bioremediation site. The polychlorinated dibenzo- p-dioxin and polychlorinated dibenzofuran content was observed to decrease in response to treatment with the fungus. The species-specific PCR technique developed in the present work is useful in evaluating the possibility of on-site bioremediation using the fungus Ceriporia sp. MZ-340.
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