by Laura Buenning
Metabolism gets a lot of hype from ads promoting exercise régimes to magazine articles targeting a weight-conscious audience. So, most of us understand metabolism as the process animals and plants go through to consume nourishment and thrive.
From humans to microbes, an organism’s metabolism selects nutritious substances, rejects poisonous ones, and organizes the sequential chemical reactions required to transform food chemicals into energy, so they can thrive. The series of steps required to get from food consumption to growth and reproduction are called metabolic pathways.
For the organism that’s where it ends; but for genetic and metabolic engineers Cong Trinh, JDRD team leader, and LDRD team leader Adam Guss of ORNL’s Biosciences Division, this is where the fun begins. Because nature creates a network of pathways, microorganisms can be redesigned to use atypical pathways and, as a result, yield different products. To Trinh and Guss, microbial metabolism offers a playground of opportunity to design miniature cell factories capable of producing valuable end products.
In this case Trinh and Guss want to reengineer microorganisms to convert biomass—fermentable sugars, lignin, chemical inhibitors—into an array of advanced biofuels. Guss’s team will redesign the bacteria E. coil to convert lignin and biomass inhibitors into isobutanol; Trinh’s team will reengineer the yeast Saccharomyces to change sugars and biomass inhibitors (specifically acetate) into biodiesel instead of ethanol, its usual end product.
Trinh says their first challenge is to map out Saccharomyces’ metabolic pathways and then design optimal biodiesel-producing, acetate-assimilating pathways the yeast can use. Computer modeling comes first followed by laboratory development of organisms with the most promising metabolic pathways predicted by their models. The project takes advantage of a huge database of information from industries that use Saccharomyces species to make bread, wine, and beer.
“Our modeling helps identify which genetic modifications will optimize biodiesel production,” Trinh says. Once Trinh, PhD graduate student Adam Thompston, and postdoc Narayan Niraula understand the genetic pathways that lead to both ethanol and biodiesel production and to acetate consumption, they can use well-established gene knockout techniques to reengineer organisms designed to consume sugars and acetate to generate biodiesels.
The dilemma? Trinh says, “Acetate is toxic. It usually inhibits growth.
“Microorganisms always ‘see’ the food they like first. Glucose is easy to ferment; they are not going to use energy to consume other substances when glucose is available. But in this case we’re going to trick the yeast into identifying acetate as a [preferred] food, engineering them to detoxify acetate by consuming and converting it into biodiesel.
“Ultimately we want to create microbial cell factories that will not only make biodiesels, but could also become a platform for other biochemicals derived from biomass,” Trinh says.
The two projects will integrate successes into platforms for isobutanol-producing E. coli and biodiesel-producing S. cerevisiae.
Redesigning yeast metabolism for optimal biodiesel production from biomass
Cong Trinh, UT Department of Chemical and Biomolecular Engineering
Synthetic metabolic pathways for bioconversion of lignin and biomass inhibitors
Adam Guss, ORNL Biosciences Division