Gene discovery may enable more efficient consolidated biorefining

By Erin Voegele | August 22, 2011

The U.S. DOE has announced a team of researchers in its BioEnergy Science Center have pinpointed the gene that controls ethanol production capacity in a microorganism. According to the department, the discovery could be the missing link in developing biomass crops that produce higher concentrations of ethanol at lower costs. A report outlining the team’s findings, titled “Mutant alcohol dehydrogenase leads to improved ethanol tolerance in Clostridium thermocellum,” has been published in the scholarly journal Proceedings of the National Academy of Sciences.

“The Department of Energy relies on the scientific discoveries of its labs and research centers to improve the production of clean energy sources,” said Energy Secretary Steven Chu. “This discovery is an important step in developing biomass crops that could increase yield of ethanol, lower production costs and help reduce our reliance on imported oil.”

According to the DOE, scientists have studied Clostridium thermocellum, a type of anaerobic bacterium, for decades, but had failed to determine a genetic basis for its ability to tolerate high concentrations of ethanol. The team that recently made that discovery leveraged the BESC partnership to draw upon multiple experts spanning several scientific disciplines to contribute a broader set of analyses. BESC is led by Oak Ridge National Laboratory, and is one of three Bioenergy Research Centers established by the DOE’s Office of Science in 2007.

The discovery of the gene that controls ethanol production in Clostridium thermocellum will allow scientists to experiment with the genetic alteration of plans to produce more ethanol. According to the DOE, scientists have been working to develop tailor-made microorganisms that produce their own enzymes to break down cell walls and release sugars, while also fermenting those sugars into ethanol in a single step. “Identifying this gene is a key step towards making the first tailor-made microorganism that produces more ethanol,” said the DOE in a statement.

The report published in PNAS states that ethanol intolerance is an important metric in terms of process economics for consolidated biorefining technologies. “Tolerance has often been described as a complex and likely multigenic trait for which complete gene interactions come into play,” said the authors in the report. “Here, we resequence the genome of an ethanol-tolerant mutant, show that the tolerant phenotype is primarily due to a mutated bifunctional acetaldehyde-CoA/alcohol dehydrogenase gene, hypothesize based on structural analysis that cofactor specificity may be affected, and confirm this hypothesis using enzyme assays…The simplicity of the genetic basis for the ethanol-tolerant phenotype observed here informs rational engineering of mutant microbial strains for cellulosic ethanol production.”