The study investigated the characteristics of aerobic degradation of tetrabromobisphenol A (TBBPA) by Irpex lacteus F17 ( I. lacteus F17) under four different cometabolic substrates (phenol, glucose, sodium pyruvate, and sodium citrate). The biodegradation of TBBPA by I. lacteus F17 could be enhanced via cometabolism, and glucose (8 g/L) was confirmed to be the optimum carbon source. For different initial solution pH ranging from 3.0 to 8.0, the results showed that I. lacteus F17 could be applied to biodegrade TBBPA in a wide pH range of 4.0–8.0, and the degradation rate could reach the maximum 75.31%, while the debromination rate reached the maximum 12.40% under pH 5.0. In addition, it has been confirmed that Mn 2+ (50 μmol/L) could promote the secretion of manganese peroxidase and TBBPA biodegradation efficiency. Seven intermediates were identified by gas chromatography–mass spectrometry analysis, and the possible degradation pathways were proposed, which indicated the biodegradation of TBBPA might be subjected to debromination, β -scission, hydroxylation, deprotonation, and oxidation reactions.
Duan Zihong,Shen Rui,Liu Binjie,Yao Mengwei,Jia Rong
Irpex lacteus F17 is well-known for its ability to degrade recalcitrant aromatic pollutants, which mainly results from the action of the manganese peroxidase (MnP) that it is able to produce. Recently, the genome sequencing and annotation of this strain provided comprehensive picture of the ligninolytic peroxidase gene family. In addition to revealing the presence of 13 MnPs, genes for five dye-decolorizing peroxidases (DyPs) were also discovered in the I. lacteus F17 genome, which are unrelated to the fungal class II peroxidases. In the present study, amino acid sequences of five DyPs and 13 MnPs, representing two different families of heme peroxidases, were analyzed. Of these, two enzymes, a DyP (Il-DyP4) and a MnP (Il-MnP6) were expressed respectively in Escherichia coli, and were characterized by comparing their molecular models, substrate specificities, and catalytic features. The results showed that Il-DyP4 possessed a higher catalytic efficiency for some representative substrates, and a stronger decolorizing ability to a wide range of synthetic dyes in acidic conditions. Based on electrochemical measurements, Il-DyP4 was found to have a high redox potential of 27 mV at pH 3.5, which was superior to that of Il-MnP6 (− 75 mV), thereby contributing to its ability to oxidize high redox potential substrates, such as veratryl alcohol and polymeric dye Poly R-478. The results highlighted the potential of Il-DyP4 for use in industrial and environmental applications.
Malachite green (MG), a recalcitrant, carcinogenic, and mutagenic triphenylmethane dye, was decolorized and detoxified using crude manganese peroxidase (MnP) prepared from the white rot fungus Irpex lacteus F17. In this study, the key factors (pH, temperature, MG, Mn 2+ , H 2 O 2 , MnP) in these processes were investigated. Under optimal conditions, 96 % of 200 mg L −1 of MG was decolorized when 66.32 U L −1 of MnP was added for 1 h. The K
m , V
max , and k
cat values were 109.9 μmol L −1 , 152.8 μmol L −1 min −1 , and 44.5 s −1 , respectively. The decolorization of MG by MnP followed first-order reaction kinetics with a kinetic rate constant of 0.0129 h −1 . UV–vis and UPLC analysis revealed degradation of MG. Furthermore, seven different intermediates formed during the MnP treatment of 0.5 h were identified by LC-TOF-MS. These degradation products were generated via two different routes by either N -demethylation of MG or the oxidative cleavage of the C–C double bond in MG. Based on ecotoxicity analyses performed on bacteria and algae, it was confirmed that MG metabolites produced by the MnP-catalyzed system were appreciably less toxic than the parent compound. These studies indicate the potential use of this enzyme system in the clean-up of aquatic and terrestrial environments.
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