Handling Several Sugars at a Time: a Case Study of Xyloglucan Utilization by <i>Ruminiclostridium cellulolyticum</i>
Clara Kampik, Nian Liu, Mohamed Mroueh, Nathalie Franche, Romain Borne, Yann Denis, Séverine Gagnot, Chantal Tardif, Sandrine Pagès, Stéphanie Perret, Nicolas Vita, Pascale de Philip, Henri-Pierre Fierobe
Abstract
The study of the decomposition of recalcitrant plant biomass is of great interest as the limiting step of terrestrial carbon cycle and to produce plant-derived valuable chemicals and energy. While extracellular cellulose degradation and catabolism have been studied in detail, few publications describe the complete metabolism of hemicelluloses and, to date, the published models are limited to the extracellular degradation and sequential entry of simple sugars. Here, we describe how the model anaerobic bacterium Ruminiclostridium cellulolyticum deals with the synchronous intracellular release of glucose, galactose, xylose, and cellobiose upon cytosolic depolymerization of imported xyloglucan oligosaccharides. The described novel metabolic strategy involves the simultaneous activity of different metabolic pathways coupled to a network of inhibitions controlling the carbon flux and is distinct from the ubiquitously observed sequential uptake and metabolism of carbohydrates known as the diauxic shift. Our results highlight the diversity of cellular responses related to a complex environment.