Plant cell walls form an abundant source of fermentable sugars for biofuels and biochemicals yet resist microbial decomposition due to their variable lignin content and composition. Model and more established platforms such as <i>T. reesei</i> and brown rot display reduced hydrolytic activity and inhibited growth with syringyl-rich lignin. Early-diverging anaerobic fungi resident in the digestive tracts of large herbivores, however, are among the most active plant-degrading microbes secreting the widest known array of biomass-degrading enzymes seemingly unbiased in substrate preference. More importantly, anaerobic fungi degrade diverse substrates with comparable efficiency through remodeling of their secretome in a substrate dependent manner. However, the regulatory inputs that are recognized remain unclear. Insight into this process would inform future genomic studies that dissect this behavior to study efficient fungal hydrolytic strategies for sustainable chemical production. Here, we evaluate the ability of these fungi to adapt to substrates of variable lignin content and composition. We have assembled a panel of novel fungal isolates from both zoo and farm animals representing several types of fungal genera. We demonstrate that these fungi express and secrete tightly regulated carbohydrate active enzymes (e.g. cellulases) that are active on a broad array of untreated agricultural residues, food wastes, and woody forestry products. More importantly, these enzymes are robust against increasing levels of syringyl lignin, which is a natural plant defense against microbial degradation. Compositional analyses of these substrates coupled with surveys of the fungal proteome reveal that anaerobic fungi recognize both polymeric content (e.g. lignin) and its monomeric composition. Increasing levels of S-lignin, while keeping lignin:cellulose:hemicellulose constant, led to the regulation of several biomass degrading enzymes. This behavior is conserved across several genera of anaerobic fungi. We are beginning to characterize this response in detail to identify the specific activities of the enzymes involved. Our work probes the rich regulatory response of plant biomass hydrolysis in anaerobic fungi, and highlights strategies honed and evolved for millennia that may be key to the efficient hydrolysis of untreated lignocellulose.<br/> <br/>

Global regulation of lignocellulolytic proteins from anaerobic fungi in response to substrate lignin content and composition

255th National Meeting (2018)

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