Super-fermenting fungus genome sequenced, to be harnessed for biofuels

Earlier this week, researchers identified which genes a bacterium activates to select the enzymes for the breakdown of cellulose into sugars. The discovery is important for the future of cellulosic ethanol production (earlier post). Another group of scientists discovered similar cellulase genes in the guts of termites - creatures famed for their capacity to break down wood efficiently (earlier post).

Today, another major research step was announced by researchers from the U.S. Department of Energy Joint Genome Institute (DOE JGI) (earlier post)and collaborators at the U.S. Forest Service, Forest Products Laboratory (FPL). They succeeded in characterising the genetic blueprint of the fungus Pichia stipitis and identified the numerous genes responsible for its fermenting and cellulose-bioconverting prowess. The research results, accompanied by an analysis of these metabolic pathways, is featured in the March 4 advanced online publication of Nature Biotechnology. Clearly, biotechnology and genomics are en route to make cellulosic ethanol production a reality.

P. stipitis is the most proficient microbial fermenter in nature of the ligno-cellulose abundant in hardwoods and agricultural leftovers, which represent a motherlode of bioenergy feedstocks.

"Increasing the capacity of P. stipitis to ferment xylose and using this knowledge for improving xylose metabolism in other microbes, such as Saccharomyces cerevisiae, brewer's yeast, offers a strategy for improved production of cellulosic ethanol. "In addition, this strategy could enhance the productivity and sustainability of agriculture and forestry by providing new outlets for agricultural and wood harvest residues." - Eddy Rubin, DOE JGI Director.

Ligno-cellulosic biomass, a complex of cellulose, hemicellulose, and lignin, is derived from such plant-based feedstocks as agricultural waste, paper and pulp, wood chips, grasses, or trees such as poplar, recently sequenced by the U.S. Department of Energy's JGI. Under current strategies for generating lignocellulosic ethanol, these forms of biomass require expensive and energy-intensive pretreatment with chemicals and/or heat to loosen up this complex. Enzymes are then employed to break down complex carbohydrate into sugars, such as glucose and xylose, which can then be fermented to produce ethanol. Additional energy is required for the distillation process to achieve a fuel-grade product. Now, the power of genomics is being directed to optimize this age-old process:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: cellulose :: lignin :: xylose :: wood :: biomass :: genomics :: biotechnology ::

"The information embedded in the genome sequence of Pichia has helped us identify several gene targets to improve xylose metabolism," says paper lead author Thomas W. Jeffries of the Forest Products Laboratory in Madison, Wisconsin. "We are now engineering these genes to increase ethanol production." Jeffries said that yeast strains like Pichia have evolved to cope with the oxygen-limited environment rich in partially digested wood that is encountered in the gut of insects, from where the sequenced strain was originally isolated.

FPL has a Cooperative Research and Development Agreement (CRADA) in place with a New York City-based bioenergy company, Xethanol Corporation, which plans to integrate Dr. Jeffries' findings into its large-scale biofuels production processes.

Pichia joins white rot fungus in the growing portfolio of bioenergy-relevant fungus genomes sequenced by DOE JGI through its user programs and contributed freely to the worldwide scientific community.

More information:
Thomas W Jeffries, Igor V Grigoriev, Jane Grimwood, José M Laplaza, Andrea Aerts, Asaf Salamov, Jeremy Schmutz, Erika Lindquist, Paramvir Dehal, Harris Shapiro, Yong-Su Jin, Volkmar Passoth & Paul M Richardson, Genome sequence of the lignocellulose-bioconverting and xylose-fermenting yeast Pichia stipitis [*abstract], Published online: 04 March 2007 | doi:10.1038/nbt1290