Metabolism of the Cellulose-Degrading Marine Bacterium Saccharophagus Degradans 2-40

Microorganisms can produce many of the fuels, polymers, and commodity chemicals that have traditionally been derived from petroleum. Ideally, the feedstock for these microorganisms would be cellulosic biomass because it is cheap and sustainable. Unfortunately, converting cellulose to fuels or other useful chemicals remains technically challenging and economically uncompetitive due, in part, to the pretreatment needed to digest the material. Saccharophagus degradans 2-40 is a marine bacterium that natively utilizes cellulosic biomass and several other complex polysaccharides using minimal pretreatment. As such, it holds considerable potential to be engineered as a cellulose-fed biofactory. Developing rational strategies for engineering S. degradans to make value-added products is aided by a detailed knowledge of the metabolic processes by which the bacterium utilizes sugars and biomass. We have characterized the metabolism of S. degradans on glucose and cellobiose, a β(1→4) glucose dimer that is the primary product of cellulosic biomass degradation, using isotope assisted metabolic flux analysis (MFA). We conducted parallel, steady-state isotope labeling experiments using uniformly and positionally ¹³C-labeled sugars. These experiments revealed a considerable (10–20%) diversion of carbon to another sugar that remained in the growth medium during growth on glucose, but not on cellobiose. Furthermore, we identified that under both conditions, the major catabolic flux mode favors NADPH production at the expense of ATP.