NOD-AOL · Nitric oxide-driven anaerobic oxidation of lignocellulose

In the riparian zone of eutrophic lakes and in field denitrification beds, microbial communities degrade lignocellulose, in anoxia, while maintaining a denitrifying lifestyle. During this process nitrate is converted to nitrogen gases via a series of reactions and intermediate products, fueled by the degradation of lignocellulosic biomass. The microbial interactions, metabolic pathways, and enzymatic mechanisms, underlining this remarkable process remain largely unknown. Intriguingly, in these anoxic habitats, enzymes involved in O2-driven oxidative lignocellulose conversion are found and expressed, yet their source of O2, their potential use of other oxidants, and their catalytic mechanism in anoxia remain unknown. Exploring this knowledge gap is a high-risk endeavor with potential to discover yet undescribed enzymes or enzyme systems capable of anaerobic oxidation of lignocellulose (AOL).I hypothesize that oxidative cleavage of lignocellulose under denitrifying conditions follows aerobic routes including lytic polysaccharide monooxygenases (LPMOs) and lignin-active oxidases, and further, that the activity of nitric oxide dismutases (NODs) provides a source of O2 for LPMOs and lignin-active enzymes. This is conceptually high risk, linking together biological processes in a new way. Herein I will scrutinize my key hypotheses by in-depth characterization of both LPMOs, lignin-active enzymes and NODs to a depth never done before. I will study whether LPMOs can employ relevant non-conventional denitrification-linked electron acceptors and use novel approaches for characterizing the enigmatic NODs.NOD-AOL is highly interdisciplinary and addresses questions central for understanding the global carbon and nitrogen cycles, which may ultimately help counteracting climate change.