Low-molecular-weight (LMW) aromatics are crucial in meditating fungal processes for plant biomass decomposition. Some LMW compounds are employed as electron donors for oxida-tive degradation in brown rot (BR), an efficient wood-degrading strategy in fungi that selectively degrades carbohydrates but leaves modified lignins. Previous understandings of LMW aromatics were primarily based on “bulk extraction”, an approach that cannot fully reflect their real-time functions during BR. Here, we applied an optimized molecular imaging method that combines matrix-assisted laser desorption ionization (MALDI) with Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) to directly measure the temporal profiles of BR aromatics as Rhodonia placenta decayed a wood wafer. We found that some phenolics were pre-existing in wood, while some (e.g., catechin-methyl ether and dihydroxy-dimethoxyflavan) were generated immediately after fungal activity. These pinpointed aromatics might be recruited to drive early BR oxidative mechanisms by generating Fenton reagents, Fe2+ and H2 O2 . As BR progressed, ligninolytic products were accumulated and then modified into various aromatic derivatives, confirming that R. placenta depolymerizes lignin. Together, this work confirms aromatic patterns that have been implicated in BR fungi, and it demonstrates the use of MALDI-FTICR-MS imaging as a new approach to monitor the temporal changes of LMW aromatics during wood degradation.
Bibliographical noteFunding Information:
Funding: This work was supported by user facility grant 50799, 51393 (J.S.S. and J.Z.) at the Environmental Molecular Sciences Laboratory (EMSL, grid.436923.9), a U.S. Department of Energy Office of Science User Facility sponsored by the Biological and Environmental Research program located at the Pacific Northwest National Laboratory (PNNL). We thank for the funding support of U.S. Department of Energy Office of Science Grants DE-SC0019427 and DE-SC0019357 from the Office of Biological and Ecological Research (BER) (J.S.S. and J.Z.).
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- Brown rot fungus
- Low-molecular aromatics
- MALDI imaging
- Rhodonia placenta
- Wood decomposition