Abstract

The cytoplasmic and membrane proteomes of the cellulolytic bacterium Clostridium thermocellum grown on either cellulose or cellobiose were quantitatively compared using a metabolic 15N isotope labelling method in conjunction with nanoLC-ESI-MS/MS. In total 1255 proteins were identified in the study and 95 of those were able to have their relative abundance per cell compared in at least one cellular compartment in response to the substrates provided. Three cellulosome anchoring proteins, OlpB, Orf2P, and SdbA, were all found to be more abundant in cellulose grown cells. Cellodextrin transport complex B, appearing to be the major cellodextrin transporter in the organism, did not demonstrate any difference in abundance on either substrate. Cellodextrin transport complex A, putatively a strict cellotriose transporter, demonstrated increased abundance in cellobiose grown cells. This study reveals that cells grown on cellulose increase their abundance of phospoenolpyruvate carboxykinase while decreasing the abundance of pyruvate kinase, suggesting that the organism diverts carbon flow into a transhydrogenase malate cycle that can increase the production of the biosynthetic intermediates NADPH and GTP. Glutamate dehydrogenase and copper amine oxidase proteins were also found to have increased abundance in cellulose grown cells, suggesting that the assimilation of ammonia is up-regulated during growth on the substrate. The up-regulation of enzymes leading to increased production of biosynthetic intermediates and the assimilation of ammonia reveal how the organism produces the substrates necessary to increase the production of cellulosomes required for the hydrolysis of crystalline cellulose.