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Bioremoval of humic acid from water by white rot fungi: exploring the removal mechanisms

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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.

No MeSH data available.


Extracellular enzymes activities of four tested fungal strains in NL and NS media with and without the presence of HA. aT. versicolor, bP. chrysosporium, cP. sajor-caju, dP. ostreatus. Note the difference in Y-axis scale
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Fig4: Extracellular enzymes activities of four tested fungal strains in NL and NS media with and without the presence of HA. aT. versicolor, bP. chrysosporium, cP. sajor-caju, dP. ostreatus. Note the difference in Y-axis scale

Mentions: The extracellular enzyme activities are shown in Fig. 4. Laccase, MnP, and LiP were measured during the incubation period. None of the fungal strains showed LiP activity except for P. chrysosporium that showed low and not verifiable (large differences in repetitions) LiP activities, on days 6 and 9 of the incubation, although for the rest of the incubation period no significant LiP activity was detected. This may be due to the several reasons that have been suggested previously, such as inhibition of LiP by humic compounds and certain difficulties of the assay method (Lackner et al. 1991; Ralph and Catcheside 1994; Hofrichter and Fritsche 1997), inhibition of LiP activity of WRF due to the agitation (shaking) of the culture (Moyson and Verachtert 1993; Zanirun et al. 2009) or the absence of veratryI alcohol in the culture media used in this study, since it can induce and mediate the LiP activity (Waldner et al. 1988; Wesenberg 2003). The lack of LiP activity in the culture of the specific strain of P. chrysosporium that we used (DSMZ 1556), is not unprecedented (Blondeau 1989). Therefore LiP activity was excluded from the graphs in Fig. 4.Fig. 4


Bioremoval of humic acid from water by white rot fungi: exploring the removal mechanisms
Extracellular enzymes activities of four tested fungal strains in NL and NS media with and without the presence of HA. aT. versicolor, bP. chrysosporium, cP. sajor-caju, dP. ostreatus. Note the difference in Y-axis scale
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120169&req=5

Fig4: Extracellular enzymes activities of four tested fungal strains in NL and NS media with and without the presence of HA. aT. versicolor, bP. chrysosporium, cP. sajor-caju, dP. ostreatus. Note the difference in Y-axis scale
Mentions: The extracellular enzyme activities are shown in Fig. 4. Laccase, MnP, and LiP were measured during the incubation period. None of the fungal strains showed LiP activity except for P. chrysosporium that showed low and not verifiable (large differences in repetitions) LiP activities, on days 6 and 9 of the incubation, although for the rest of the incubation period no significant LiP activity was detected. This may be due to the several reasons that have been suggested previously, such as inhibition of LiP by humic compounds and certain difficulties of the assay method (Lackner et al. 1991; Ralph and Catcheside 1994; Hofrichter and Fritsche 1997), inhibition of LiP activity of WRF due to the agitation (shaking) of the culture (Moyson and Verachtert 1993; Zanirun et al. 2009) or the absence of veratryI alcohol in the culture media used in this study, since it can induce and mediate the LiP activity (Waldner et al. 1988; Wesenberg 2003). The lack of LiP activity in the culture of the specific strain of P. chrysosporium that we used (DSMZ 1556), is not unprecedented (Blondeau 1989). Therefore LiP activity was excluded from the graphs in Fig. 4.Fig. 4

View Article: PubMed Central - PubMed

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.

No MeSH data available.