Sunday, April 29, 2007 - 3:30 PM

Genomics of cellulosic ethanol-producing bacteria

Jizhong Zhou and Chris Hemme. Institute for Environmental Genomics, University of Oklahoma, 101 David L. Boren Blvd, Norman, OK 73019

The genomes of three strains of ethanol-producing bacteria (Thermoanaerobacter ethanolicus 39E, T. ethanolicus X514 and Clostridium cellulolyticum) have been sequenced.  Strain 39E was isolated from a Yellowstone hot spring and is relatively well-characterized.  Strain X514 is a metal-reducing bacteria isolated from the deep subsurface and is predicted to have been geographically isolated from 39E for ~200 MY.  Both strains are capable of metabolizing glucose and xylan to ethanol with a novel bifunctional secondary alcohol dehydrogenase serving as the terminal enzyme in the pathway.  Slight differences are noted in the carbon metabolism of the two strains, including a complete KDPG metabolism pathway in 39E and the lack of a complete methylglyoxal shunt in X514.  A survey of unique genes between the strains reveals lineage-specific gene expansions in the two strains including individual unique sugar transporter profiles and an increased number of P-type metal translocating ATPase genes in X514.  C. cellulolyticum employs a large extracellular cellulosome complex to degrade these materials and comparisons with a previously sequenced genome of C. thermocellum suggest a significant diversity in cellulosome composition.  To complement this research, a request for sequencing the genomes of an additional 20 ethanol-producing Clostridia strains has been approved by JGI.  Strains were chosen from among the genera Clostridium, Thermoanaerobacter, Thermoanaerobacterium and Acetivibrio based on prior knowledge, phylogeny, unique physiology and industrial applications.  The expansion of the genomic database of industrially-important Clostridia is expected to provide substantial benefits in the understanding of this class of organisms.

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