Roberta L. Farrell

Industrial applications of lignin-transforming enzymes

Lignin-degrading and modifying enzymes are produced under specific culture conditions by white-rot fungi. Most of these enzymes are excreted into the extracellular environment and can be purified from culture supernatant. At RepliGen we have characterized many of the extracellular proteins from the white-rot fungus Phanerochaete chrysosporium. Industrial application potentials for these enzymes are predicted to be in the chemical industry, pulp and paper industry, and perhaps in pollution control. The isolation and characterization of enzymes that catalyse specific reactions on kraft lignins and lignosulphonates will be discussed. These reactions include (1) a polymerizing—depolymerizing activity that changes the size of the lignin substrate and (2) a decolorizing reaction that reduces chromophoric groups in lignin. Kraft lignin and lignosulphonates have many diverse commercial applications because of their dual properties of hydrophobicity and hydrophilicity. They could have broad use if modified, as in the above reactions, in an efficient manner. The development of enzyme systems may provide just such efficient reactions.

A New Key Enzyme for Lignin Degradation

At Repligen Corporation our goal is to produce lignin-degrading and -modifying enzyme products. The major applications of these products may be in the pulp and paper industry. Integration into pulping and bleaching operations of these enzymes, which in essence are biocatalysts, could be of great benefit to the industry in several ways. ( 1) Lignin-degrading enzymes may be integrated into existing bleaching schemes to displace chlorine-based oxidizing agents in the bleaching of chemical pulp. These highly selective biocatalysts should markedly reduce damage to cellulosic fibers, which results in poor strength qualities, and eliminate the environmental release of polluting lignin-derived chlorinated aromatic compounds. They may also minimize plant corrosion costs and contribute directly to extending the bleach plant life cycle. (2) Lignin-degrading enzymes may be used to partially delignify coarse thermomechanical pulp (TMP). Further processing of T M P will yield a higher-quality product manufactured with substantially less energy than used by existing thermomechanical processes. (3) Lignin-modifying enzymes may selectively attack the free phenol groups in lignin while leaving the bulk of the lignin unchanged. This process may significantly reduce the brightness reversion of chemical and mechanical pulps without eliminating the high yield contributed by lignin. (4) Lignin-degrading and -modifying enzymes can decolorize the effluent from bleaching plants. Color in bleach effluents results from the presence of complex, environmentally hazardous chlorinated aromatic compounds. Enzymes will decolorize these compounds and facilitate their decomposition. The use of lignin-degrading and -modifying enzymes has evolved from the results of several laboratories around the world using biological organisms in pulp and bleach operations. Eriksson and his co-workers of the Swedish Forest Products Research Laboratory pioneered the use of cellulase-less mutant white-rot fungi in pretreating wood chips to save energy before refining! Cultures of white-rot fungi were shown by T. Kent Kirk and co-workers a t the U.S.D.A. Forest Products Laboratory and by Hou-min Chang, Thomas Joyce, and collaborators a t North Carolina State University to cause partial delignification of kraft pulp and to decolorize bleach plant E l effluent.* The enzymes Repligen is developing are isolated either from organisms like the white-rot fungus, Phanerochaete chrysosporium or from recombinant organisms which express genes which we have cloned from either P. chrysosporium or other organisms. In this paper I will discuss some recent work on ligninolytic enzymes and their possible applications. Lignin constitutes 17-33% of dry wood weight? It is the second most abundant polymer in the world but its current utility is limited. The role of lignin is to cement the plysaccharide components in cell walls both chemically and physically, thus increas-

Enzymatic treatment of lignochemicals; adhesive and resin uses

Abstract The possibility of upgrading lignochemicals for use in the adhesives industry through the application of biotechnology was investigated. It was hypothesized that ligninolytic organisms or isolated ligninolytic enzymes might modify lignin in such a manner as to make it more reactive as a copolymer in adhesive manufacturing. The following discussion takes the form of three sections; the first discusses some background on lignin degradation and describes the isolation and characterization of fungal and recombinant ligninolytic enzymes. The second section describes the making of PVA/lignochemical glues and the results of modifying, both chemically and enzymatically, the lignochemicals used in those glues. Finally, the last section describes the effects observed upon treatment of a variety of lignochemicals, kraft lignins and lignosulfonates, with recombinant H8 (rH8), a lignin peroxidase whose gene was cloned from Phanerochaete chrysosporium .