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Mechanisms and Regulation of Cellulose Degradation by Clostridia papyrosolvens C7 and Neurospora crassa


Microbial degradation of plant biomass plays a central role in the global carbon cycle. However, the turnover of cellulose in plants poses a difficult challenge due to its microcrystalline nature and its protection by other polymers in the plant cell wall. Bacteria and fungi have evolved diverse strategies for breaking down plant biomass, involving suites of cellulolytic enzymes that are produced at appropriate times to degrade the recalcitrant substrate. The work presented here provides an analysis of two cellulolytic organisms and their potential as model systems in the study of cellulose degradation.

We probed the cellulolytic system in Clostridium papyrosolvens C7 by sequencing its genome and characterizing the cellulosomal components. Comparisons to other cellulosome producing organisms revealed many unique enzymes and non-catalytic cellulosome components. When grown on different carbon sources, C. papyrosolsovens C7 upregulates enzymes incorporated into cellulosomes with surprisingly little compositional diversity or dynamic range. These results provide a framework for using C. papyrosolvens C7 in the engineering of designer cellulosomes, as well as understanding the regulation and efficiency of these heterogeneous multienzyme complexes.

The tools available for studying N. crassa have recently been applied to its cellulolytic system and much has been quickly learned about its degradative capability. However, the processes that produce its strong and specific induction of cellulase genes are not well understood. Through a screen for deletion strains that affect cellulose degradation, a kinase (NCU07399) was identified that seems to affect the transcriptional activation of several cellulase genes. Preliminary characterization of this kinase reveals an unusual domain architecture and in vitro phosphorylation activity that mimic studies on its yeast and human homologs. The screen and subsequent assays used to analyze NCU07399 presented here should provide a basis for dissecting the pathways involved in cellulase upregulation by N. crassa.

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