Sulfur tuft and turkey tail: biosynthesis and biodegradation of organohalogens by Basidiomycetes

Trichloroacetic acid in Norway spruce/soil-system. I. Biodegradation in soil

Trichloroacetic acid (TCA) as a phytotoxic substance affects health status of coniferous trees. It is known as a secondary air pollutant (formed by photooxidation of tetrachloroethene and 1,1,1-trichloroethane) and as a product of chlorination of humic substances in soil. Its break-down in soil, however, influences considerably the TCA level, i.e. the extent of TCA uptake by spruce roots. In connection with our investigations of TCA effects on Norway spruce, microbial processes in soil were studied using 14C-labeling. It was shown that TCA degradation in soil is a fast process depending on TCA concentration, soil properties, humidity and temperature. As a result, the TCA level in soil is determined by a steady state between uptake from the atmosphere, formation in soil, leaching and degradation. The process of TCA degradation in soil thus participates significantly in the chlorine cycle in forest ecosystems.

Dechlorination of chlorobenzenes by a culture containing bacterium DF-1, a PCB dechlorinating microorganism

Polychlorinated benzenes were reductively dechlorinated by an enrichment culture containing the polychlorinated biphenyl (PCB) dechlorinating bacterium DF-1. The culture dechlorinated hexachlorobenzene (hexa-CB) --> pentachlorobenzene (penta-CB) --> 1,2,3,5-tetrachlorobenzene (1,2,3,5-CB) --> 1,3,5-trichlorobenzene (1,3,5-CB) and did not dechlorinate other tetrachlorobenzenes or any trichlorobenzenes. This restricted series of reactions is the most predominant and frequently reported pathway for the dechlorination of hexa-CB and penta-CB by enrichment cultures inoculated with either freshwater or estuarine sediments. The culture did not dechlorinate hydroxylated and methoxylated polychlorinated benzenes or a hydroxylated PCB. Bacterium DF-1 was detected by PCR/DGGE analysis following dechlorination of penta-CB but was not detected when a chlorinated benzene (CB) was not dechlorinated; detection of other members in the communitywas unaffected by the presence or absence of CB dechlorination. This is the first report of a bacterium that reductively dechlorinates both PCBs and CBs and the first identification of an organism that can dechlorinate a CB with more than four chlorines.

Biocatalytic chlorination of aromatic hydrocarbons by chloroperoxidase of Caldariomyces fumago

Chloroperoxidase from Caldariomyces fumago was able to chlorinate 17 of 20 aromatic hydrocarbons assayed in the presence of hydrogen peroxide and chloride ions. Reaction rates varied from 0.6 min(-1) for naphthalene to 758 min(-1) for 9-methylanthracene. Mono-, di- and tri-chlorinated compounds were obtained from the chloroperoxidase-mediated reaction on aromatic compounds. Dichloroacenaphthene, trichloroacenaphthene, 9,10-dichloroanthracene, chloropyrene, dichloropyrene, dichlorobiphenylene and trichlorobiphenylene were identified by mass spectral analyses as products from acenaphthene, anthracene, pyrene and biophenylene respectively. Polycyclic aromatic hydrocarbons with 5 and 6 aromatic rings were also substrates for the chloroperoxidase reaction. The importance of the microbial chlorination of aromatic pollutants and its potential environmental impact are discussed.

Chlorometabolite production by the ecologically important white rot fungus Bjerkandera adusta

Two strains of the basidiomycete, Bjerkandera adusta (DAOM 215869 and BOS55) produce in static liquid culture, phenyl, veratryl, anisyl and chloroanisyl metabolites (CAM's) (alcohols, acids and aldehydes) as well as a series of compounds not previously known to be produced by Bjerkandera species: 1-phenyl, 1-anisyl, 1-(3-chloro-4-methoxy) and 1-(3,5-dichloro-4-methoxy) propan-1,2-diols, predominantly as erythro diastereomers with IR, 2S absolute configurations. 1-Anisyl-propan-1,2-diol and 1-(3,5-dichloro-4-methoxy)-propan-1,2-diol are new metabolites for which the names Bjerkanderol A and B, respectively, are proposed. Experiments with static liquid cultures supplied with 13C6- and 13C9-L-phenylalanine showed that all identified aromatic compounds (with the exception of phenol) can be derived from L-phenylalanine. For the aryl propane diols, the 13C label appeared only in the phenyl ring and the benzylic carbon, suggesting a stereoselective re-synthesis from a C7 and a C2-unit, likely aromatic aldehyde and decarboxylated pyruvate, respectively. Other compounds newly discovered to be derived from phenylalanine by this white rot fungus include phenylacetaldehyde and phenylpyruvic, phenylacetic, phenyllactic, mandelic and phenyl glyoxylic (benzoyl formic) acids. For both strains, cultures supplied with Na37Cl showed incorporation of 37Cl in all identified chlorometabolites. Veratryl alcohol and the CAM alcohols, which occur in both strains and can be derived from L-phenylalanine (all 13C-labelled), have reported important physiological functions in this white rot fungus. Possible mechanisms for their formation through the newly discovered compounds are discussed.

Bacterial community changes and enrichment of Burkholderia-like bacteria induced by chlorinated benzoates in a peat-forest soil-microcosm

Bacterial community shifts in a peat-forest soil spiked with 3-chlorobenzoate (3CBA) or 2,5-dichlorobenzoate (2,5DCB) were monitored by PCR-amplification of the V6 to V8 regions of the 16S rRNA and rDNA, followed by separation of the amplicons by temperature gradient gel electrophoresis. 3CBA disappeared to non-detectable levels after 15 days by a biologically mediated process, while 2,5DCB remained at the initial concentration values. The experiments were conducted under microcosms systems. Addition of the chlorinated benzoates to the soil resulted in a rapid decrease of the microbial diversity, as judged by a time-dependent reduction in the number of amplicons detected by temperature gradient gel electrophoresis. Few amplicons specifically enriched in the spiked soils were cloned and characterised by sequence analysis. The identity of the cloned DNA and the corresponding soil amplicons was confirmed by hybridisation with a radioactively labelled V6-probe. Analysis of the 16S rDNA sequences indicated that Burkholderia-related bacteria dominated the enriched soil populations under 3CBA stress. In addition, enrichment cultures growing on 3CBA as sole C-source were obtained from the respective spiked soil, which were found to contain bacteria with identical 16S rDNA sequences as those induced by 3CBA stress in soil.

Hydroxylated metabolites of 2,4-dichlorophenol imply a fenton-type reaction in Gloeophyllum striatum

While degrading 2,4-dichlorophenol, two strains of Gloeophyllum striatum, a basidiomycetous fungus causing brown rot decay of wood, simultaneously produced 4-chlorocatechol and 3,5-dichlorocatechol. These metabolites were identified by comparing high-performance liquid chromatography retention times and mass spectral data with those of chemically synthesized standards. Under similar conditions, 3-hydroxyphthalic hydrazide was generated from phthalic hydrazide, a reaction assumed to indicate hydroxyl radical formation. Accordingly, during chemical degradation of 2,4-dichlorophenol by Fenton's reagent, identical metabolites were formed. Both activities, the conversion of 2,4-[U-(14)C]dichlorophenol into (14)CO(2) and the generation of 3-hydroxyphthalic hydrazide, were strongly inhibited by the hydroxyl radical scavenger mannitol and in the absence of iron. These results provide new evidence in favor of a Fenton-type degradation mechanism operative in Gloeophyllum.

Degradation of ciprofloxacin by basidiomycetes and identification of metabolites generated by the brown rot fungus Gloeophyllum striatum

Ciprofloxacin (CIP), a fluoroquinolone antibacterial drug, is widely used in the treatment of serious infections in humans. Its degradation by basidiomycetous fungi was studied by monitoring 14CO2 production from [14C]CIP in liquid cultures. Sixteen species inhabiting wood, soil, humus, or animal dung produced up to 35% 14CO2 during 8 weeks of incubation. Despite some low rates of 14CO2 formation, all species tested had reduced the antibacterial activity of CIP in supernatants to between 0 and 33% after 13 weeks. Gloeophyllum striatum was used to identify the metabolites formed from CIP. After 8 weeks, mycelia had produced 17 and 10% 14CO2 from C-4 and the piperazinyl moiety, respectively, although more than half of CIP (applied at 10 ppm) had been transformed into metabolites already after 90 h. The structures of 11 metabolites were elucidated by high-performance liquid chromatography combined with electrospray ionization mass spectrometry and 1H nuclear magnetic resonance spectroscopy. They fell into four categories as follows: (i) monohydroxylated congeners, (ii) dihydroxylated congeners, (iii) an isatin-type compound, proving elimination of C-2, and (iv) metabolites indicating both elimination and degradation of the piperazinyl moiety. A metabolic scheme previously described for enrofloxacin degradation could be confirmed and extended. A new type of metabolite, 6-defluoro-6-hydroxy-deethylene-CIP, provided confirmatory evidence for the proposed network of congeners. This may result from sequential hydroxylation of CIP and its congeners by hydroxyl radicals. Our findings reveal for the first time the widespread potential for CIP degradation among basidiomycetes inhabiting various environments, including agricultural soils and animal dung.

Biotransformation of the major fungal metabolite 3,5-dichloro- p-anisyl alcohol under anaerobic conditions and its role in formation of Bis(3,5-dichloro-4-Hydroxyphenyl)methane

Higher fungi have a widespread capacity for biosynthesis of organohalogens. Commonly occurring chloroaromatic fungal metabolites can end up in anaerobic microniches at the boundary of fungal colonies and wetland soils. The aim of this study was to investigate the environmental fate of a major fungal metabolite, 3, 5-dichloro-p-anisyl alcohol, under anaerobic conditions. This compound was incubated with methanogenic sludge to study its biotransformation reactions. Initially, 3,5-dichloro-p-anisyl alcohol was readily demethylated in stoichiometric quantities to 3, 5-dichloro-4-hydroxybenzyl alcohol. The demethylated product was converted further via two routes: a biotic route leading to the formation of 3,5-dichloro-4-hydroxybenzoate and 2,6-dichlorophenol, as well as an abiotic route leading to the formation of bis(3, 5-dichloro-4-hydroxyphenyl)methane. In the first route, the benzyl alcohol moiety on the aromatic ring was oxidized, giving 3, 5-dichloro-4-hydroxybenzoate as a transient or accumulating product, depending on the type of methanogenic sludge used. In sludge previously adapted to low-molecular-weight lignin from straw, a part of the 3,5-dichloro-4-hydroxybenzoate was decarboxylated, yielding detectable levels of 2,6-dichlorophenol. In the second route, 3, 5-dichloro-4-hydroxybenzyl alcohol dimerized, leading to the formation of a tetrachlorinated bisphenolic compound, which was identified as bis(3,5-dichloro-4-hydroxyphenyl)methane. Since formation of this dimer was also observed in incubations with autoclaved sludge spiked with 3,5-dichloro-4-hydroxybenzyl alcohol, it was concluded that its formation was due to an abiotic process. However, demethylation of the fungal metabolite by biological processes was a prerequisite for dimerization. The most probable reaction mechanism leading to the formation of the tetrachlorinated dimer in the absence of oxygen is presented, and the possible environmental implications of its natural occurrence are discussed.