Friday, August 12, 2011

Direct Biomass to Alcohol: Boosting Yields from Clostridium Thermocellum

The discovery of the gene controlling ethanol production in a microorganism known as “Clostridium thermocellum” will mean that scientists can now experiment with genetically altering biomass plants to produce more ethanol. Current methods to make ethanol from a type of biomass found in switchgrass and agricultural waste require the addition of expensive enzymes to break down the plant’s barriers that guard energy-rich sugars. Scientists, including those at BESC, have been working to develop a more streamlined approach in which tailor-made microorganisms produce their own enzymes that unlock the plant’s sugars and ferment them into ethanol in a single step. Identifying this gene is a key step towards making the first tailor-made microorganism that produces more ethanol. _Energy.gov_via_GCC
Clostridium thermocellum is a promising bacterium capable of direct biomass to alcohol transformation. Oak Ridge National Labs scientists are learning how to make C. thermocellum more tolerant of higher ethanol concentrations, so that it can produce higher concentrations of ethanol. Such improved yields should reduce the overall costs of ethanol, and eventually the same approach will be used to achieve higher yields of other chemicals from biomass.
Ethanol intolerance is an important metric in terms of process economics, and tolerance has often been described as a complex and likely multigenic trait for which complex gene interactions come into play. 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 (adhE), hypothesize based on structural analysis that cofactor specificity may be affected, and confirm this hypothesis using enzyme assays.

...Future determination of compounds resisted by these strains may reveal the selective pressures that led to evolution of altered cofactor specificity of AdhE and suggest further paths for metabolic engineering of this organism for industrial biofuel production. Finally, the ability to identify and characterize sets of biological components linked to desired phenotypes, such as the mutated AdhE gene in this study, or overexpression of endogenous genes offers the prospect for improved rational design of systems in the future that will be best suited to particular feedstocks and desired processes. _GCC

Another study on the metabolic analysis of C. thermocellum for improved bioethanol production

As mentioned many times here at AFE, the race is on between different approaches to produce high yields of biofuels and high yield chemicals directly from biomass and wastes.
  • The above approach involves exhaustive genomic studies of promising organisms, with focused alterations of the genome.
  • Another approach involves the attempt to "pack the genome" of a particular microbe with all the enzyme-genes it will need to carry out all the necessary reactions to produce the fuel or chemical from the inexpensive feedstock.
  • Yet another approach involves the use of multiple micro-organisms working as a team, either in batch form, in stages, or separated by membranes which are permeable to the chemicals of interest.
  • Still another approach will utilise biological enzymes packaged inside protective spheres which allow them to catalyse specific reactions but protect them from potentially harmful compounds in the broth.
  • Finally, the use of nanotechnological catalysts, mimics of biological enzymes, is likely to be the ultimate winner of this contest -- given the greater hardiness of non-organic materials to potentially toxic alcohols and chemicals.
Al Fin has often joked about developing a strain of yeast which will let him brew 100 proof beer with a simple homebrew kit. While such an achievement may have to wait a while, if scientists can jazz up a microbe to achieve fermentation yields of 20% or more alcohol from cheap biomass or waste, the cost of biofuels is likely to take a nosedive.

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