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Title: CO2-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.more » 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.« less
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [1] ;  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. of California, Los Angeles, CA (United States)
  3. Univ. of California, Los Angeles, CA (United States); Academia Sinica, Taipei City (Taiwan)
Publication Date:
Report Number(s):
Journal ID: ISSN 0027-8424
Grant/Contract Number:
AC36-08GO28308; LDRD #0627-1403; Fuel Cell Technologies Office DE-AC36-08-GO28308; Bioenergy Technologies Office; BioEnergy Science Center
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 46; Journal ID: ISSN 0027-8424
National Academy of Sciences, Washington, DC (United States)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Program (EE-3F); USDOE Office of Energy Efficiency and Renewable Energy (EERE), NREL Laboratory Directed Research and Development (LDRD)
Country of Publication:
United States
09 BIOMASS FUELS; Clostridium thermocellum; CO2 utilization; formate; C-isotopic tracing; one-carbon metabolism; C1 metabolism; 59 BASIC BIOLOGICAL SCIENCES
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1335804