Fungal Redox Enzymes Involved in the Oxidation of Organic Pollutants

Abstract: This work describes the degradation of nonylphenol, toxaphene, phenanthrene, benzo[a]pyrene and dyes using fungi and their redox enzymes. Two fungi, Bjerkandera sp. strain BOL13 and Fusarium sp. strain BOL35 were isolated from different geographic area in Bolivia. They were characterized genetically, physiologically and biochemically. Degradation of nonylphenol by Bjerkandera sp. strain BOL13 and T. versicolor was achieved in liquid cultures, as well as in polluted soil. Since laccase activity was detected in cultures of T. versicolor, an enzymatic mechanism appears be involved in its degradation. In contrast, in cultures of Bjerkandera sp strain BOL13 neither manganese peroxidase (MnP) nor lignin peroxidase (LiP) was detected, and a mechanism of free radicals may be involved. Phenanthrene degradation was achieved in a liquid medium by Bjerkandera sp. strain BOL13. MnP and LiP activity were detected in the cultures. Phenanthrene degradation was confirmed using extracellular fluid rich in enzyme activity. MnP can be active over a broad pH range, from 5 to 7. However, degradation at low pH in liquid media is preferable, since the optimal pH for lignin modifying enzyme activities are in the acidic range. Toxaphene, an organic chlorinated pesticide, was removed by Bjerkandera sp. strain BOL13. Waste biomass was used as co-substrate. The removal was related to LiP and xylanase activity. Wheat husk proved to be a better substrate for the production of LiP. Xylose the product of xylanase activity may be the source of H2O2. Several dyes, including Reactive red 2 and Reactive blue 4 were decolorized by Bjerkandera sp. strain BOL13. A continuous biological contactor was operated with a low-nitrogen and low-glucose content medium. This kind of reactor may be suitable for large-scale decolorization. The decolorization of dyes was better at acid pH. Operating the reactor at neutral pH, led to decrease in decolorization activity. As was expected, neither LiP nor MnP activity was detected at that pH. At neutral pH a coupling reaction was observed. This reaction was Mn2+ dependant, but interestingly was not required H2O2. Both phenanthrene and anthracene were degraded by combining MnP and the Fenton reagent. Degradation was attributed to the capability of the MnP to reduce Fe3+ and oxidize Fe2+. The reaction was carried in a liquid medium as well as in polluted soil at pH close to neutral. However, the Fenton reaction carried out at pH 3, showed better performance in removing PAHs. Degradation of organic pollutants at neutral pH or close are desirable, since native microorganisms can be affected at low pH, and the release of toxic heavy metals is favored in acidic pH. A mixture of two proteins with LiP and MnP activities was purified partially from Bjerkandera sp. strain BOL13. This mixture may be responsible for the degradation of recalcitrant compound with this strain. Fusarium sp strain BOL35 was characterized as a new species Fusarium santarosense. The fungus was able to degrade BaP. Laccase was present in its cultures. The production of a red pigment in the cultures was noticed. The absorption spectrum of the purified pigment was comparable to those obtained from naphthoquinone, common metabolites produced by Fusarium spp. Since degradation of BaP by F. santarosense can be attributed to a mechanism in which laccase and quinones, are involved. Laccase was characterized from Fusarium sp. strain BOL35. Dimethylated and tetramethylated aromatic compounds were found to be better substrates for the enzyme. The enzyme showed a different UV-Visible spectrum from those of blue laccase or yellow laccase, but its spectrum was comparable to those of white laccase, although with different substrate specificity.