Metabolism of glucose and cellobiose by cellulolytic mesophilic Clostridium sp. strain H10

Abstract

The metabolism of strain H10, a cellulolytic mesophilic Clostridium sp., was studied on glucose and cellobiose as energy and carbon sources. The main products of fermentation of both sugars were acetate, lactate, and ethanol. At low sugar levels, molar growth yields were better for cellobiose than for glucose. In both cases, an inhibition of growth was observed between 1 and 2 g/liter and a total inhibition after the latter concentration. Inhibition was not the result of low pH due to acid formation; growth under static pH conditions was limited in the same way. On the other hand, acetate and lactate had no inhibitory effect when added at concentrations equal to the final titers. Concomitant with the inhibition of growth was a change in metabolic pathways for sugar concentrations between 1 and 2 g/liter, i.e., the production of lactate was higher. After complete inhibition of growth, an accumulation of carbohydrates which were neither glucose nor cellobiose was observed.

Clostridium cellulolyticum: model organism of mesophilic cellulolytic clostridia

“…Whereas the effects of acidic conditions on the growth of cellulolytic rumen bacteria have been the subject of considerable research [133][134][135][136][137], few investigations have been devoted to cellulolytic clostridia. Contrary to the assumption that the buffering capacity of the culture medium is sufficient to compensate the acidification [97,99], reinvestigation of cellulose degradation by C. cellulolyticum demonstrated that the growth inhibition observed with batch cultures, performed in penicillin flasks, is essentially the result of a low pH due to acid production in the course of fermentation. Cellulose-limited chemostats confirmed the dramatic effect of environmental acidification which influences chiefly biomass formation rather than cellulose degradation and assimilation [98].…”

“…The accumulation of G1P leads to the rerouting of metabolism through, first, the production of glycogen and, second, the exopolysaccharide biosynthesis. In C. cellulolyticum, the presence of uncharacterised exopolysaccharides was suggested early [97]. The synthesis of glycogen was also reported but contrary to ruminal cellulolytic bacteria where it can represent between 30% and 60% of the dry weight [153], in C. cellulolyticum its accumulation is limited to between 3% and 5% [150].…”

Relationships between cellobiose catabolism, enzyme levels, and metabolic intermediates inClostridium cellulolyticum grown in a synthetic medium

“…The main products of cellobiose fermentation by C. cellulolyticum were acetate, ethanol, lactate, H 2 , and CO 2 (Giallo et al, 1983); because of the very low concentrations of extracellular pyruvate detected in the medium, we have omitted this compound in the reactions leading to the formation of the metabolites. Strobel et al (1995) demonstrated in C. thermocellum that the transport of cellodextrin, cellobiose, or glucose was ATP-dependent and that intracellular cellobiose was converted to glucose 1-phosphate and glucose by cellobiose phosphorylase (EC 2.4.1.20) (Giallo, 1984).…”

“…In most natural environments, mesophilic cellulolytic clostridia play a major role in cellulose decomposition Leschine, 1995), and it became apparent that their biotechnological exploitation necessitates knowledge about biomass formation and metabolic features which control the rates, yields, and kinds of fermentation products. Clostridium cellulolyticum, a mesophilic bacterium able to degrade crystalline cellulose (Petitdemange et al, 1984) has been studied with regard to its ability to use various substrates (Giallo et al, 1983(Giallo et al, , 1985Gelhaye et al, 1993a,b;Payot et al, 1998).…”

“…Using cellobiose as carbon source, since this disaccharide is the major end-product of the cellulose degradation process (Ng and Zeikus, 1982;Strobel et al, 1995), we have shown that C. cellulolyticum, as other cellulolytic clostridia, metabolized only a small quantity of soluble carbohydrate (Giallo et al, 1983;Benoit et al, 1992). To improve C. cellulolyticum cellobiose consumption and growth, rich media containing yeast extract, casamino acids, and vitamin cocktail have been used without success; nevertheless, complex media have been used systematically (Giallo et al, 1983(Giallo et al, ,1985Benoit et al, 1992;Cailliez et al, 1992;Gelhaye et al, 1993a,b). Continuous cultures were examined to determine the physiological basis of this poor growth (Payot et al, 1998).…”