Transcriptomic and proteomic changes from medium supplementation and strain evolution in high-yielding Clostridium...

Area of Science:

• Microbial biotechnology
• Synthetic biology
• Bioenergy research

Background:

• Clostridium thermocellum is a key organism for lignocellulosic biofuel production due to its direct cellulose degradation and ethanol conversion capabilities.
• Engineered strains exhibit enhanced ethanol yields but often suffer from reduced growth rates, hindering industrial application.
• Previous attempts to improve growth, such as adaptive laboratory evolution and medium supplementation, have yielded unclear underlying mechanisms.

Purpose of the Study:

• To elucidate the physiological impacts of metabolic engineering, evolution, and formate supplementation on Clostridium thermocellum growth.
• To investigate the role of C1 metabolism and stress response pathways in engineered strains.
• To identify mechanisms limiting growth in high-ethanol-producing mutants.

Main Methods:

• Comparative transcriptomics and proteomics analysis of wild-type C. thermocellum, mutant AG553, and evolved mutant AG601.
• Growth experiments with and without formate supplementation.
• Analysis of gene expression related to C1 metabolism and stress responses, including sporulation.

Main Results:

• Formate supplementation significantly improved growth in both AG553 and AG601 strains.
• Formate addition modulated the expression of C1 metabolism genes, supporting its role in providing biosynthetic units.
• Mutant AG553 exhibited significant upregulation of stress response and sporulation genes, which was absent in the evolved AG601 strain.

Conclusions:

• Formate supplementation benefits engineered C. thermocellum by supplying C1 units for biosynthesis.
• The sporulation cascade appears to be a major growth limitation in the engineered AG553 strain.
• Understanding stress responses and growth mechanisms is crucial for rational strain improvement in Clostridium thermocellum for enhanced biofuel production.