CO 2 -fixing one-carbon metabolism in a cellulose-degrading bacterium Clostridium thermocellum
Clostridium thermocellum can ferment cellulosic biomass to formate and other end products, including CO2. This organism lacks formate dehydrogenase (Fdh), which catalyzes the reduction of CO2 to formate. However, feeding the bacterium 13C-bicarbonate and cellobiose followed by NMR analysis showed the production of 13C-formate in C. thermocellum culture, indicating the presence of an uncharacterized pathway capable of converting CO2 to formate. Combining genomic and experimental data, we demonstrated that the conversion of CO2 to formate serves as a CO2 entry point into the reductive one-carbon (C1) metabolism, and internalizes CO2 via two biochemical reactions: the reversed pyruvate:ferredoxin oxidoreductase (rPFOR), which incorporates CO2 using acetyl-CoA as a substrate and generates pyruvate, and pyruvate-formate lyase (PFL) converting pyruvate to formate and acetyl-CoA. We analyzed the labeling patterns of proteinogenic amino acids in individual deletions of all five putative PFOR mutants and in a PFL deletion mutant. We identified two enzymes acting as rPFOR, confirmed the dual activities of rPFOR and PFL crucial for CO2 uptake, and provided physical evidence of a distinct in vivo 'rPFOR-PFL shunt' to reduce CO2 to formate while circumventing the lack of Fdh. Such a pathway precedes CO2 fixation via the reductive C1 metabolic pathway in C. thermocellum. Lastly, these findings demonstrated the metabolic versatility of C. thermocellum, which is thought of as primarily a cellulosic heterotroph but is shown here to be endowed with the ability to fix CO2 as well.
- Research Organization:
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Hydrogen Fuel Cell Technologies Office (HFTO); USDOE Office of Energy Efficiency and Renewable Energy (EERE), NREL Laboratory Directed Research and Development (LDRD)
- Grant/Contract Number:
- LDRD #0627-1403; Fuel Cell Technologies Office DE-AC36-08-GO28308; Bioenergy Technologies Office; BioEnergy Science Center; AC36-08GO28308
- OSTI ID:
- 1330469
- Alternate ID(s):
- OSTI ID: 1335804
- Report Number(s):
- NREL/JA-2700-67201
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Vol. 113 Journal Issue: 46; ISSN 0027-8424
- Publisher:
- National Academy of Sciences, Washington, DC (United States)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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