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2013|14 Annual Report Fraunhofer IGB

Lignin – a natural source of aromatic compounds The cell walls of woody plant material consist of the com- posite material lignocellulose which is made up of the com- ponents cellulose, hemicellulose and lignin. Being a primary constituent of straw and wood, lignocellulose accumulates in large quantities as a waste material from agriculture and forestry and therefore is not in direct competition with food production. All components of this renewable raw material are used within the concept of a lignocellulose biorefinery. Cellulose and hemicellulose can be isolated from lignocel- lulose, hydrolyzed and the sugar monomers obtained can be converted chemically or by fermentation into many different chemicals. Lignin has until now primarily been used to gener- ate energy, but it offers major potential for utilization as a building block in polymers. Lignin is formed from a combina- tion of coniferyl alcohol, sinapyl alcohol and coumaryl alcohol and is the biggest natural source of aromatic compounds. Lignin can be used in the form of aromatic oligomers or monomers for the substitution of lots of petrochemically- based plastics and chemicals such as polyurethanes, synthetic resins or phenol. To do this, the lignin polymer must first be broken down at least partially and the pieces functionalized to become synthesis buildings blocks. Here, enzymatic meth- ods promise ecologically efficient and selective conversion of lignin. Lignin-modifying enzymes from fungi White-rot fungi are the most well-known examples of lignin- degrading organisms. In the enzymatic degradation process of these fungi, predominantly the enzyme categories lignin, manganese and versatile peroxidases and laccases play an important role. The lignin peroxidases have a high redox po- tential and are capable of attacking non-phenolic structures in lignin directly. Manganese peroxidases oxidize Mn(II) to Mn(III), which in turn diffuses into the lignin molecule and oxi- dizes phenolic structures. The versatile peroxidases are hybrids of lignin and manganese peroxidases. Laccases have a low re- dox potential and can only attack non-phenolic structures by means of mediators [1]. Apart from the laccases, these lignin- modifying enzymes are only available at very high prices. An optimization of the production process for lignin, manganese and versatile peroxidases therefore continues to represent a challenge. At the IGB it has been possible, through the co- cultivation of different strains of fungi in submerged culture, to achieve an increase in the production of lignin-modifying enzymes [2] (Fig. 1). In collaboration with the Fraunhofer CBP, the yield of ligninolytic enzymes in submerged fungal cultures has been further optimized and transferred to a larger scale of up to 10 liters. Bacterial lignin degradation In addition to the production of ligninolytic enzymes from fungi, bacterial lignin degradation is also being researched. Some bacterial strains within the group of actinomycetes and among the α- and γ-proteobacteria capable of breaking down lignin are described in the relevant literature [3]. The bacterial mechanism of lignin degradation and its enzymatic background have, however, hardly been researched yet. In the culture supernatants of ligninolytic bacterial strains cultivated with lignin we have been able to detect peroxidase and lac- case enzyme activity (Fig. 2). In order to exploit new bacterial enzymes, we are also studying the genomes of ligninolytic bacteria. Here, both DyP-type peroxidases, which may be 10 4 NEW ENZYMES FOR THE MODIFICATION OF LIGNIN Dipl.-Biol. (t. o.) Dominik Rais, Priv.-Doz. Dr. Steffen Rupp, Dr.-Ing. Susanne Zibek CHEMISTRY 1 2 0 activity[U / ​l] 600 500 400 300 200 100 laccase manganese peroxidase lignin peroxidase strain 1 strain 2 strain 3 strain 4 strain 5 strain 6 strain 7

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