CARBOHYDRATE TRANSPORT BY THE ANAEROBIC THERMOPHILE CLOSTRIDIUM-THERMOCELLUM LQRI

Clostridium thermocellum is an anaerobic thermophilic bacterium which degrades cellulose and ferments the resulting glucose, cellobiose, and cellodextrins predominantly to ethanol, However, relatively little in formation was available on carbohydrate uptake by this bacterium, Wash ed cells internalized intact oligomers as large as cellopentaose, Sinc e cellobiose and cellodextrin phosphorylase activities were detected i n the cytosol and were not associated with cell membranes, phosphoryla tion of carbohydrates occnrred intracellularly, Kinetic studies indica ted that cellobiose and larger cellodextrins were taken up by a common uptake system while glucose entered via a separate mechanism. When ce lls were treated with metabolic inhibitors including iodoacetate and a rsenate, the uptake of radiolabeled glucose or cellobiose was reduced by as much as 90%, and this reduction was associated with a 95% declin e in intracellular ATP content. A combination of the ionophores nigeri cin and valinomycin abolished the proton-motive force but only slightl y decreased transport and ATP, These results suggested that the two mo des of carbohydrate transport in C. thermocellum were ATP dependent, T his work is the first demonstration of cellodextrin transport by a cel lulolytic bacterium.