Indian Journal of Microbiology

, Volume 48, Issue 2, pp 252–266

Pyruvate catabolism and hydrogen synthesis pathway genes of Clostridium thermocellum ATCC 27405

  • Carlo R. Carere
  • Vipin Kalia
  • Richard Sparling
  • Nazim Cicek
  • David B. Levin
Original Article

DOI: 10.1007/s12088-008-0036-z

Cite this article as:
Carere, C.R., Kalia, V., Sparling, R. et al. Indian J Microbiol (2008) 48: 252. doi:10.1007/s12088-008-0036-z

Abstract

Clostridium thermocellum is a gram-positive, acetogenic, thermophilic, anaerobic bacterium that degrades cellulose and carries out mixed product fermentation, catabolising cellulose to acetate, lactate, and ethanol under various growth conditions, with the concomitant release of H2 and CO2. Very little is known about the factors that determine metabolic fluxes influencing H2 synthesis in anaerobic, cellulolytic bacteria like C. thermocellum. We have begun to investigate the relationships between genome content, gene expression, and end-product synthesis in C. thermocellum cultured under different conditions. Using bioinformatics tools and the complete C. thermocellum 27405 genome sequence, we identified genes encoding key enzymes in pyruvate catabolism and H2-synthesis pathways, and have confirmed transcription of these genes throughout growth on α-cellulose by reverse transcriptase polymerase chain reaction. Bioinformatic analyses revealed two putative lactate dehydrogenases, one pyruvate formate lyase, four pyruvate:formate lyase activating enzymes, and at least three putative pyruvate:ferredoxin oxidoreductase (POR) or POR-like enzymes. Our data suggests that hydrogen may be generated through the action of either a Ferredoxin (Fd)-dependent NiFe hydrogenase, often referred to as “Energy-converting Hydrogenases”, or via NAD(P)Hdependent Fe-only hydrogenases which would permit H2 production from NADH generated during the glyceraldehyde-3-phosphate dehydrogenase reaction. Furthermore, our findings show the presence of a gene cluster putatively encoding a membrane integral NADH:Fd oxidoreductase, suggesting a possible mechanism in which electrons could be transferred between NADH and ferredoxin. The elucidation of pyruvate catabolism pathways and mechanisms of H2 synthesis is the first step in developing strategies to increase hydrogen yields from biomass. Our studies have outlined the likely pathways leading to hydrogen synthesis in C. thermocellum strain 27405, but the actual functional roles of these gene products during pyruvate catabolism and in H 2 synthesis remain to be elucidated, and will need to be confirmed using both expression analysis and protein characterization.

Keywords

Clostridium thermocellum Fermentation Cellulose Hydrogen Pyruvate catabolism 

Copyright information

© Association of Microbiologists of India 2008

Authors and Affiliations

  • Carlo R. Carere
    • 1
  • Vipin Kalia
    • 2
  • Richard Sparling
    • 3
  • Nazim Cicek
    • 1
  • David B. Levin
    • 1
  1. 1.Department of Biosystems EngineeringUniversity of ManitobaWinnipegCanada
  2. 2.Microbial Biotechnology and Genomics, Institute of Genomics and Integrative Biology (IGIB); Council of Scientific and Industrial Research (CSIR)Delhi University CampusDelhiIndia
  3. 3.Department of MicrobiologyUniversity of ManitobaWinnipegCanada