Mechanisms of Humic Acids Degradation by White Rot Fungi Explored Using ¹H NMR Spectroscopy and FTICR Mass Spectrometry

Abstract

Enzymatic activities involved in decay processes of natural aromatic macromolecules, such as humic acids (HA) and lignin by white rot fungi, have been widely investigated. However, the physical and chemical analysis of degradation products of these materials has not been intensively explored. Fourier transform cyclotron resonance mass spectrometry (FTICR MS) and 1H NMR as well as CHNOS and size exclusion chromatography were employed to study the mechanisms of HA degradation by Trametes sp. M23 and Phanerochaete sp. Y6. Size exclusion chromatography analyses demonstrate and provide evidence for HA breakdown into low MW compounds. The 1H NMR analysis revealed oxidation, a decrease in the aromatic content, and an indication of demethylation of the HA during biodegradation. Evidence for oxidation was also obtained using CHNOS. Analysis of FTICR MS results using a new software program developed by our group (David Mass Sort) revealed consecutive series of masses suggesting biochemical degradation trends such as oxidation, aromatic cleavage, and demethylation. These results are in agreement with the 1H NMR analysis and with the suggested role of the ligninolytic system leading to HA degradation.

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

“…Some previous studies used decolorization as a measurement of degradation of HA (Kabe et al 2005; Grinhut et al 2011b), based on research were decolorization of HA was observed when degradation of HA was also proven (Grinhut et al 2011a). The co-occurrence of the decolorization and degradation of HA was also observed in our study; however, decolorization was not necessarily representing the degradation of HA.…”

“…The removal of HA by WRF has been studied before, and It was shown that WRF can degrade humic acid (Ralph and Catcheside 1997; Grinhut et al 2011a). However, there are still ambiguities regarding the level of biosorption and degradation/transformation of HA by WRF.…”

“…The decolorization of an HA solution has been accepted as an indication of the decrease in HA concentration in that solution (Stevenson 1995), which could be due to degradation, conversion or sorption of HA. Yet the decolorization has also been used to estimate the degradation of HA (Grinhut et al 2011a, b). The ability of laccase to degrade HA has been studied before.…”

Soil organic carbon contents, aggregate stability, and humic acid composition in different alpine grasslands in Qinghai-Tibet Plateau

“…The labile fractions of SOC, such as water-soluble organic carbon (WSOC) and easily oxidizable organic carbon (EOC), have been considered as more sensitive indicators for land use changes compared to SOC (Yang et al 2009a). On the other hand, most SOC exists as chemically resistant humic substances, namely, humic acid (HA), fulvic acid (FA) and humin (HU), which constitute approximately 60%-75% of SOC (Grinhut et al 2011). Owing to their refractory properties, humic substances play a crucial role in soil carbon sequestration (Swift 2001).…”

Extending the analytical window for water-soluble organic matter in sediments by aqueous Soxhlet extraction

“…In the last decade, ultrahigh-resolution Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry (FT-ICR MS) has extended the analytical window for organic matter characterization due to its capacity for resolving thousands of constituents with individual elemental compositions in complex DOM mixtures. FT-ICR MS provided insights into the sources of DOM in various environments (Kim et al, 2004;Koch et al, 2005;Dittmar and Koch, 2006;Hertkorn et al, 2006;Tremblay et al, 2007;Reemtsma et al, 2008;Schmidt et al, 2009;Bhatia et al, 2010;D'Andrilli et al, 2010;Lechtenfeld et al, 2013;Roth et al, 2013) and it revealed transformation of DOM related to microbial processes (Kim et al, 2006;Longnecker and Kujawinski, 2011;Schmidt et al, 2011), fungal degradation (Grinhut et al, 2011), and photochemical alteration (Kujawinski et al, 2004;Gonsior et al, 2009).…”