Researchers at Rice University have genetically modified a form of E. coli bacteria that can metabolize glucose and produce almost pure succinate — a key ingredient of many plastics, solvents, drugs, and food additives. With dwindling fossil-fuel reserves and rising energy costs, it's no wonder that finding "green" methods to make chemical intermediates like succinate is becoming a high priority for the chemical industry.
"The DOE has also targeted succinate for biosynthesis," says process codeveloper George Bennett, professor and chair of the department of biochemistry and cell biology at Rice. "One reason for this is succinate's broad utility — it can be used to make everything from noncorrosive airport deicers and nontoxic solvents to plastics, drugs, and food additives. Succinate's also a priority because some bacteria make it naturally, so we have a metabolic starting place for large-scale fermentation."
The key to Rice's technology is a mutant form of E. coli that makes succinate as it's only metabolic by-product. The bug contains more than a half-dozen genetic modifications. It was created over the past four years by the research groups of Bennett and fellow Rice professor Ka-Yiu San.
The technology has taken its first step from the lab to the marketplace with the recent start of industrial scale-up efforts in Kansas. Bennett and San are working with Kansas-based AgRenew Inc., which began testing farm-grown products like grain sorghum to serve as feedstocks for the succinate-producing bacteria. The goal is to maximize the conversion speed and yield of succinate produced per pound of glucose converted.
Bennett and San reportedly used a few clever metabolic engineering tricks to create their bug, which can produce succinate in two different ways. One method exists in wild strains of E. coli and has been modified with the deletion of four genes, each of which codes for a protein that interferes with or limits E. coli's ability to turn glucose into succinate. Bennett and San activated a second pathway and stimulated production by adding genes from lactococcus bacteria and sorghum.
Each genetic pathway metabolizes glucose and produces succi-nate via dissimilar chemical reactions. That means the two don't compete or interfere with one another. "Our experiments in the laboratory have produced near-maximum yields, with almost all the glucose being converted into succinate," said San. The research at Rice University is funded by the National Science Foundation, while the USDA has supported related research within AgRenew Inc.
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