The transformation of lignin, a waste product of biorefineries, into a commercially valuable biochemical advances with the discovery of an enzyme that attacks the stubborn bonds of monomer units. When inserted into a bioengineered bacterium, the enzyme efficiently converts lignin compounds into muconic acid, a common component of plastics.

Researchers from U.S. Oak Ridge National Laboratory, U.S. National Renewable Energy Laboratory and the University of Tennessee identified the enzyme used by the microbe Novosphingobium aromaticivorans to degrade linkages in 1,2-diguaiacylpropane-1,3-diol (DGPD), a particularly strong lignin dimer. Tests confirmed the role of this enzyme and revealed that a better-known and understood enzyme played a complementary role in further breaking down DGPD into useful compounds.

The enzyme isolated from one microbe, left, was inserted with another lignin-degrading enzyme into another engineered bacterium. Source: Joshua K. Michener et al.

Both enzymes were then inserted into a strain of the bacterium Pseudomonas putida that had already been engineered to produce muconic acid. As a result, the bacterium converted DGPD into the value-added precursor for plastics at a nearly 100% yield.

The research, which also has implications for biofuel production, is published in Metabolic Engineering.