Title: CO ₂ -fixing one-carbon metabolism in a cellulose-degrading bacterium Clostridium thermocellum

Abstract

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

Authors:

Xiong, Wei; Lin, Paul P.; Magnusson, Lauren; Warner, Lisa; Liao, James C.; Maness, Pin-Ching; Chou, Katherine J.

Publication Date:

Fri Oct 28 00:00:00 EDT 2016

Research Org.:

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Org.:

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)

OSTI Identifier:

1330469

Alternate Identifier(s):

OSTI ID: 1335804

Report Number(s):

NREL/JA-2700-67201
Journal ID: ISSN 0027-8424

Grant/Contract Number:  

LDRD #0627-1403; Fuel Cell Technologies Office DE-AC36-08-GO28308; Bioenergy Technologies Office; BioEnergy Science Center; AC36-08GO28308

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 113 Journal Issue: 46; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences, Washington, DC (United States)

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; 09 BIOMASS FUELS; Clostridium thermocellum; CO2 utilization; formate; C-isotopic tracing; one-carbon metabolism; C1 metabolism