Biodegradation of TNT (2,4,6-trinitrotoluene) by Phanerochaete chrysosporium.

Extensive biodegradation of TNT (2,4,6-trinitrotoluene) by the white rot fungus Phanerochaete chrysosporium was observed. At an initial concentration of 1.3 mg/liter, 35.4 +/- 3.6% of the [14C]TNT was degraded to 14CO2 in 18 days. The addition of glucose 12 days after the addition of TNT did not stimulate mineralization, and, after 18 days of incubation with TNT only, about 3.3% of the initial TNT could be recovered. Mineralization of [14C]TNT adsorbed on soil was also examined. Ground corncobs served as the nutrient for slow but sustained degradation of [14C]TNT to 14CO2 such that 6.3 +/- 0.6% of the [14C]TNT initially present was converted to 14CO2 during the 30-day incubation period. Mass balance analysis of liquid cultures and of soil-corncob cultures revealed that polar [14C]TNT metabolites are formed in both systems, and high-performance liquid chromatography analyses revealed that less than 5% of the radioactivity remained as undegraded [14C]TNT following incubation with the fungus in soil or liquid cultures. When the concentration of TNT in cultures (both liquid and soil) was adjusted to contamination levels that might be found in the environment, i.e., 10,000 mg/kg in soil and 100 mg/liter in water, mineralization studies showed that 18.4 +/- 2.9% and 19.6 +/- 3.5% of the initial TNT was converted to 14CO2 in 90 days in soil and liquid cultures, respectively. In both cases (90 days in water at 100 mg/liter and in soil at 10,000 mg/kg) approximately 85% of the TNT was degraded. These results suggest that this fungus may be useful for the decontamination of sites in the environment contaminated with TNT.     

Comparative biodegradation of alkyl halide insecticides by the white rot fungus, Phanerochaete chrysosporium (BKM-F-1767).

The ability of Phanerochaete chrysosporium to degrade six alkyl halide insecticides (aldrin, dieldrin, heptachlor, chlordane, lindane, and mirex) in liquid and soil-corncob matrices was compared by using 14C-labeled compounds. Of these, only [14C]lindane and [14C]chlordane underwent extensive biodegradation, as evidenced by the fact that 9.4 to 23.4% of these compounds were degraded to 14CO2 in 30 days in liquid cultures and 60 days in soil-corncob cultures inoculated with P. chrysosporium. Although [14C]aldrin, [14C]dieldrin, [14C]heptachlor, and [14D]mirex were poorly mineralized, substantial bioconversion occurred, as determined by substrate disappearance and metabolite formation. Nonbiological disappearance was observed only with chlordane and heptachlor.     

Degradation of environmental pollutants byPhanerochaete chrysosporium

The white rot fungi appear to be unique in their ability to degrade lignin by the secretion of hydrogen peroxide and a family of peroxidases now referred to as lignin peroxidases or simply ligninases. The fact that these enzymes are naturally secreted and seem to be capable of initiating the oxidation of lignin by a free-radical mechanism led to the proposal and demonstration that the white rot fungi are able to degrade a wide variety of normally very recalcitrant environmental pollutants. The mineralization of chemicals byPhanerochaete chrysosporium does seem to be dependent upon the lignin degrading system. Thus it should be possible to at least initiate degradation extracellularly, eliminating the need for absorption of the chemical. The nonspecific nature of the system gives the potential for oxidation of a wide variety of chemicals and even mixtures of chemicals. As the lignin peroxidases are synthesized and secreted in response to nutrient starvation there is no requirement for conditioning of the organism. Mineralization can occur in either a water or soil matrix using very economical agricultural or wood wastes as nutrients. The lignin peroxidases can be purified from the extracellular fluid quite easily by fast protein liquid chromatography. They are somewhat typical peroxidases but also have some unique properties. The oxidation of some xenobiotics has been demonstrated and cooxidation is also a possible mechanism.     

Iron-catalyzed reactions may be responsible for the biochemical and biological effects of asbestos

The most carcinogenic forms of asbestos contain iron to levels as high as 36% by weight and catalyze many of the same biochemical reactions that freshly prepared solutions of iron do, i.e. oxygen consumption, generation of reactive oxygen species, lipid peroxidation and DNA damage. The participation of iron from asbestos in these reactions has been demonstrated using the iron chelator desferrioxamine B which inhibits iron-catalyzed reactions. Iron appears to be redox active on the asbestos fiber, but chelation and subsequent iron mobilization from asbestos by a variety of chelators, e.g. citrate, EDTA or nitrilotriacetate, makes the iron more redox active resulting in greater oxygen consumption and production of oxygen radicals in the presence of reducing agents. Iron also appears to be important for some of the asbestos-dependent biological effects on tissues or cells in culture, such as phagocytosis, cytotoxicity, lipid peroxidation and DNA damage. Therefore, redox cycling of iron to generate oxygen radicals at the surface of the fiber and/or in solution, as mobilized, low molecular weight chelates, may be very important in eliciting some of the biological effects of asbestos in vivo.     

The mechanism of liver microsomal lipid peroxidation.

In the presence of Fe-3+ and complexing anions, the peroxidation of unsaturated liver microsomal lipid in both intact microsomes and in a model system containing extracted microsomal lipid can be promoted by either NADPH and NADPH : cytochrome c reductase or by xanthine and xanthine oxidase. Erythrocuprein effectively inhibits the activity promoted by xanthine and xanthine oxidase but produces much less inhibition of NADPH-dependent peroxidation. The singlet-oxygen trapping agent, 1, 3-diphenylisobenzofuran, had no effect on NADPH-dependent peroxidation but strongly inhibited the peroxidation promoted by xanthine and xanthine oxidase. NADPH-dependent lipid peroxidation was also shown to be unaffected by hydroxyl radical scavengers.. The addition of catalase had no effect on NADPH-dependent lipid peroxidation, but it significantly increased the rate of malondialdehyde formation in the reaction promoted by xanthine and xanthine oxidase. The results demonstrate that NADPH-dependent lipid peroxidation is promoted by a reaction mechanism which does not involve either superoxide, singlet oxygen, HOOH, or the hydroxyl radical. It is concluded that NADPH-dependent lipid peroxidation is initiated by the reduction of Fe-3+ followed by the decomposition of hydroperoxides to generate alkoxyl radicals. The initiation reaction may involve some form of the perferryl ion or other metal ion species generated during oxidation of Fe-2+ by oxygen.     

The mechanism of liver microsomal lipid peroxidation

In the presence of Fe³⁺ and complexing anions, the peroxidation of unsaturated liver microsomal lipid in both intact microsomes and in a model system containing extracted microsomal lipid can be promoted by either NADPH and NADPH : cytochrome c reductase or by xanthine and xanthine oxidase. Erythrocuprein effectively inhibits the activity promoted by xanthine and xanthine oxidase but produces much less inhibition of NADPH-dependent peroxidation. The singlet-oxygen trapping agent, 1,3-diphenylisobenzofuran, had no effect on NADPH-dependent peroxidation but strongly inhibited the peroxidation promoted by xanthine and xanthine oxidase. NADPH-dependent lipid peroxidation was also shown to be unaffected by hydroxyl radical scavengers.. The addition of catalase had no effect on NADPH-dependent lipid peroxidation, but it significantly increased the rate of malondialdehyde formation in the reaction promoted by xanthine and xanthine oxidase. These results demonstrate that NADPH-dependent lipid peroxidation is promoted by a reaction mechanism which does not involve either superoxide, singlet oxygen, HOOH, or the hydroxyl radical. It is concluded that NADPH-dependent lipid peroxidation is initiated by the reduction of Fe³⁺ followed by the decomposition of hydroperoxides to generate alkoxyl radicals. The initiation reaction may involve some form of the perferryl ion or other metal ion species generated during oxidation of Fe²⁺ by oxygen.     

Phenotypic changes and gene expression in human colon mucosal epithelial cells upon transfection of a SV40 DNA-GPT recombinant

Summary Phenotypic changes (increased longevity, decreased growth factor requirements, altered cell surface features, growth in semisolid agarose, and SV40 T antigen expression) suggesting in vitro transformation were displayed by human normal colon mucosal epithelial cells transfected with pSV3gpt, a pBR322 recombinant containing the SV40 “early” T antigen coding region and the dominant selectable marker bacterial gene, xanthine-guanine phosphoribosyltransferase. In contrast, control cultures which received neither DNA nor the recombinatn pSV2gpt (which is identical to pSV3gpt but lacks the SV40 T antigen region) were not phenotypically altered.     

NADPH-dependen lipid peroxidation catalyzed by purified NADPH-cytochrome C reductase from rat liver microsomes

A purified preparation of rat liver microsomal NADPH-cytochrome c reductase has been shown to catalyze the NADPH-dependent peroxidation of isolated microsomal lipid. In addition to ADP and ferric ion required for NADPH-dependent lipid peroxidation in whole microsomes, this system requires high ionic strength and a critical concentration of EDTA. The peroxidation activity can be inhibited by superoxide dismutase suggesting that the superoxide anion, produced by this flavoprotein, is involved in the lipid peroxidation reaction.