Differential metabolism of cellobiose and glucose by Clostridium thermocellum and Clostridium thermohydrosulfuricum

Abstract

Clostridium thermohydrosulfuricum consumed glucose in preference to cellobiose as an energy source for growth. The rates of substrate uptake in glucoseand cellobiose-grown cell suspensions were 45 and 24 nmol/min per mg (dry weight), respectively, at 65°C. The molar growth yields (i.e., grams of cells per mole of glucose equivalents) were similar on cellobiose and glucose (19 and 16, respectively). Both glucose-and cellobiose-grown cells contained a glucose permease activity and high levels of hexokinase (>0.34 ,umol/min per mg of protein at 40°C). Growth on cellobiose was associated with induction of a cellobiose permease activity. In contrast, Clostridium thermocellum metabolized cellobiose in preference to glucose as an energy source and displayed lower growth rates on both substrates. The substrate uptake rates in cellobioseand glucose-grown cell suspensions were 18 and 17 nmol/min per mg (dry weight), respectively. The molar yields were 38 on cellobiose and 20 on glucose. Extracts of glucoseand cellobiosegrown cells both contained cellobiose phosphorylase and phosphoglucomutase activities, whereas only glucose-grown cells contained detectable levels of glucose permease and hexokinase activities. The general catalytic and kinetic properties of the glucose-and cellobiose-catabolizing enzymes in the two species are described, and a model is proposed to distinguish differential saccharide metabolism by these thermophilic ethanologens.

A Lipid‐Anchored Binding Protein is a Component of an ATP‐Dependent Cellobiose/Cellotriose‐Transport System from the Cellulose Degrader Streptomyces reticuli

“…In addition to S. rericuli, other cellulose degraders, such as the bacteria Clostridium thermocellum ( Ng and Zeikus, 1982), Ruminococcus fluvefuciens (Helaszek and White, 1991 ), and Thermomonosporu curvuta (Bernier and Stutzenberger, 1987), take up cellobiose. However, neither the biochemical nor the genetic characteristics of these systems have been elucidated.…”

A cellulase/xylanase-negative mutant of Streptomyces lividans 1326 defective in cellobiose and xylobiose uptake is mutated in a gene encoding a protein homologous to ATP-binding proteins

“…No studies describing the xylobiose transport system have been reported in the literature. Cellobiose transport has been studied in Clostridium thermocellum (Ng and Zeikus, 1982), Thermomonospora curvata (Bernier and Stutzenberger, 1987), Candida wickerhamfi and Clavispora lusitaniae (Freer and Greene, 1990) and Streptococcus bovis (Martin and Russell, 1987). A cellobiose phosphotransferase system has been reported for Bacillus stearothermophilus (Lai and Ingram, 1993) which resembles the system described for Escherichia coli (Hall and Xu, 1992).…”

Dual mechanisms of xylose uptake in the thermophilic bacterium Thermoanaerobacter thermohydrosulfuricus

“…Sodium-driven transport mechanisms for amino acids have been reported in Clostridium fervidus [14] and Bacillus stearothermophilus [15], but until recently there was little information on the mechanisms of carbohydrate transport by thermophilic bacteria. Thermophiles did not have a PTS for glucose or cellobiose [16][17][18]. Some mesophilic bacteria have facilitated diffusion systems for glucose [19,20], and recent work indicated that T. thermohydrosulfuricus Rt8.B1 had a low affinity glucose uptake system that did not require sodium or a protonmotive force [3].…”