Abstract
Twelve white rot fungi (WRF) strains were screened on agar plates for their ability to bleach humic acid (HA). Four fungal strains were selected and tested in liquid media for removal of HA. Bioremediation was investigated by HA color removal and changes in the concentration and molecular size distribution of HA by size exclusion chromatography. Trametes versicolor and Phanerochaete chrysosporium showed the highest HA removal efficiency, reaching about 80%. Laccase and manganese peroxidase were measured as extracellular enzymes and their relation to the HA removal by WRF was investigated. Results indicated that nitrogen limitation could enhance the WRF extracellular enzyme activity, but did not necessarily increase the HA removal by WRF. The mechanism of bioremediation by WRF was shown to involve biosorption of HA by fungal biomass and degradation of HA to smaller molecules. Also, contradicting previous reports, it was shown that the decolorization of HA by WRF could not necessarily be interpreted as degradation of HA. Biosorption experiments revealed that HA removal by fungal biomass is dependent not only on the amount of biomass as the sorbent, but also on the fungal species. The involvement of cytochrome P450 (CYP) enzymes was confirmed by comparing the HA removal capability of fungi with and without the presence of a CYP inhibitor. The ability of purified laccase from WRF to solely degrade HA was proven and the importance of mediators was also demonstrated.
Highlights
Humic substances Humic substances are the most widespread natural organic substances that are ubiquitous in the environment, both aquatic and terrestrial
Based on growth and bleaching results of the prescreening experiments (Table 1), four strains of White rot fungi (WRF), Pleurotus sajor-caju MES03464, Pleurotus ostreatus MES00036, T. versicolor DSMZ 3086 and Phanerochaete chrysosporium DSMZ 1556 were selected for screening in the liquid phase
Biosorption of humic acid (HA) by deactivated fungi The biosorption of HA by deactivated WRF is apparent from the results shown in Fig. 6, and it seems to be dependent on fungal species as well as the amount of biomass as sorbent
Summary
Humic substances Humic substances are the most widespread natural organic substances that are ubiquitous in the environment, both aquatic and terrestrial. White rot fungi White rot fungi (WRF) are the most abundant wood degraders in nature, which possess the unique ability of efficiently degrading lignin to CO2 (Hataka 2005; Abdel-Hamid et al 2013). They are able to decompose several aromatic pollutants or xenobiotics and can be used in (waste) water treatment (Pinedo-Rivilla et al 2009; Nguyen et al 2014). CYPs are involved in the biosynthesis of secondary metabolites and ergosterol, and in catabolic reactions that lead to the degradation of xenobiotic compounds (Aranda 2016)
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