Deciphering Cellodextrin and Glucose Uptake in Clostridium thermocellum.

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Clostridium thermocellum is a thermophilic bacterium with significant potential in lignocellulose biorefineries.
• Efficient sugar uptake is crucial for microbial cell factories and industrial applications.
• Five putative ATP-binding cassette (ABC) transporters are known in C. thermocellum for cellulose hydrolysate uptake.

Purpose of the Study:

• To identify the specific glucose and cellodextrin transporters in Clostridium thermocellum.
• To elucidate the structural mechanisms underlying transporter specificities.
• To investigate the role of sugar transporters in cellulosome production regulation.

Main Methods:

• Genetic manipulation (gene inactivation).
• Biophysical titration experiments (isothermal titration calorimetry, NMR).
• X-ray crystallography to determine protein structures.
• Biochemical assays to assess transporter function.

Main Results:

• Transporter A is the primary glucose transporter, and Transporter B is the major cellodextrin transporter in C. thermocellum.
• Crystal structures revealed specific interactions between transporters and their respective saccharides.
• The previously unknown ATPase gene (clo1313_2554) for Transporter B was identified and its structure solved.
• Deletion of Transporter B genes abolished cellobiose and cellulose induction of cellulosome production, indicating a link between sugar transport and gene regulation.

Conclusions:

• Transporter A and B are the principal transporters for glucose and cellodextrins, respectively, in C. thermocellum.
• Structural data provide insights into the molecular basis of substrate specificity.
• The ATPase component of Transporter B was identified, completing the transporter assembly.
• Sugar transport, particularly by Transporter B, is coupled to the regulation of cellulosome production, offering targets for strain engineering.