Tire manufacturer Goodyear (Akron, OH) and biotechnology company Genencor (Rochester, NY) are hard at work on a method for using bacteria to manufacture isoprene, the chemical used to make tire rubber as well as such disposable medical products as IV components. While the companies have been engineering isoprene-producing bacteria from biomass-derived sugars, ramping up production has been difficult. Now, however, Genencor has announced that modifications to the metabolic pathways of the microbes has improved yields of its trademarked product BioIsoprene.As reported in Technology Review from MIT (Cambridge, MA), a microbe such as E. coli makes small amounts of isoprene as part of its metabolism. While Genencor bioengineers initially attempted to increase yields by changing two metabolic pathways that converge to create an isoprene precursor, yields remained low because the bacteria's existing genetic machinery takes a meandering path to create isoprene from this precursor. To overcome this limitation, the company has mixed the E. coli with a plant gene coding for isoprene synthase, an enzyme that converts the precursor directly into isoprene.Next year, Genencor will decide whether to building a BioIsoprene pilot plant. Meanwhile, the company is still trying to up the yields. "We've determined the crystal structure of the [plant] enzyme and are in the process of modifying it," remarks Rich Laduca, Genencor's senior director of business development. As part of that effort, the company is experimenting with transplanting the metabolic pathways it has developed into other bacteria that grow faster.