Udo Hölker

Bio: Udo Hölker is an academic researcher from University of Bonn. The author has contributed to research in topics: Laccase & Fusarium oxysporum. The author has an hindex of 14, co-authored 22 publications receiving 1430 citations.

Biotechnological advantages of laboratory-scale solid-state fermentation with fungi.

Abstract: Despite the increasing number of publications dealing with solid-state (substrate) fermentation (SSF) it is very difficult to draw general conclusion from the data presented This is due to the lack of proper standardisation that would allow objective comparison with other processes Research work has so far focused on the general applicability of SSF for the production of enzymes, metabolites and spores, in that many different solid substrates (agricultural waste) have been combined with many different fungi and the productivity of each fermentation reported On a gram bench-scale SSF appears to be superior to submerged fermentation technology (SmF) in several aspects However, SSF up-scaling, necessary for use on an industrial scale, raises severe engineering problems due to the build-up of temperature, pH, O2, substrate and moisture gradients Hence, most published reviews also focus on progress towards industrial engineering The role of the physiological and genetic properties of the microorganisms used during growth on solid substrates compared with aqueous solutions has so far been all but neglected, despite the fact that it may be the microbiology that makes SSF advantageous against the SmF biotechnology This review will focus on research work allowing comparison of the specific biological particulars of enzyme, metabolite and/or spore production in SSF and in SmF In these respects, SSF appears to possess several biotechnological advantages, though at present on a laboratory scale only, such as higher fermentation productivity, higher end-concentration of products, higher product stability, lower catabolic repression, cultivation of microorganisms specialized for water-insoluble substrates or mixed cultivation of various fungi, and last but not least, lower demand on sterility due to the low water activity used in SSF

Extracellular laccases in ascomycetes Trichoderma atroviride and Trichoderma harzianum.

Abstract: Laccase activity in Trichoderma harzianum and in our own isolate Trichoderma atroviride was correlated with the production of the green pigment in conidial spores. The laccases of the two fungal species exhibit comparable kinetic parameters, pH optima and thermal sensitivity but differed in physiological properties, such as their catalytic activity during growth.

Hortaea acidophila, a new acid-tolerant black yeast from lignite.

Abstract: A hitherto undescribed black yeast was isolated from an extract of brown coal containing humic and fulvic acids at pH 0.6. The fungus showed morphological similarity to some members of the genus Exophiala (Chaetothyriales) and of Hortaea (Dothideales). Based on SSU rDNA sequence similarity to meristematic members of the Dothideales, the new species was accommodated in Hortaea, which presently contains only a single, halophilic species, H. werneckii.

Solubilization of low-rank coal by Trichoderma atroviride: evidence for the involvement of hydrolytic and oxidative enzymes by using 14C-labelled lignite.

Abstract: The deuteromycete Trichoderma atroviride is able to solubilize lignite in dependence on a given carbon source for growth. When cultivated on media containing glutamate, this mold excreted a set of different enzymes with hydrolytic activity. Addition of lignite to the growth media induced the synthesis of extracellular lignite-specific esterase activity but no evidence has been provided for its direct involvement in the process of lignite solubilization. Hence, the basic capability of T. atroviride enzymes to degrade a variety of ester and ether bonds at the surface or within the bulky lignite structure was tested using coal following its direct labelling with 14C-alkyl iodide. The participation of hydrolytic and oxidative enzymes in lignite degradation was assessed by measuring the release of 14C radioactivity from selectively alkylated carboxylic and phenolic OH groups. T. atroviride cleaved both carboxylic esters using esterases and the phenolic ether bonds by using oxidative enzymes, most likely laccases. Journal of Industrial Microbiology & Biotechnology (2002) 28, 207–212 DOI: 10.1038/sj/jim/7000232

Fungal laccases - occurrence and properties.

Abstract: Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.

Expansion of the enzymatic repertoire of the CAZy database to integrate auxiliary redox enzymes

Abstract: Since its inception, the carbohydrate-active enzymes database (CAZy; http://www.cazy.org ) has described the families of enzymes that cleave or build complex carbohydrates, namely the glycoside hydrolases (GH), the polysaccharide lyases (PL), the carbohydrate esterases (CE), the glycosyltransferases (GT) and their appended non-catalytic carbohydrate-binding modules (CBM). The recent discovery that members of families CBM33 and family GH61 are in fact lytic polysaccharide monooxygenases (LPMO), demands a reclassification of these families into a suitable category. Because lignin is invariably found together with polysaccharides in the plant cell wall and because lignin fragments are likely to act in concert with (LPMO), we have decided to join the families of lignin degradation enzymes to the LPMO families and launch a new CAZy class that we name “Auxiliary Activities” in order to accommodate a range of enzyme mechanisms and substrates related to lignocellulose conversion. Comparative analyses of these auxiliary activities in 41 fungal genomes reveal a pertinent division of several fungal groups and subgroups combining their phylogenetic origin and their nutritional mode (white vs. brown rot). The new class introduced in the CAZy database extends the traditional CAZy families, and provides a better coverage of the full extent of the lignocellulose breakdown machinery.

Microbial drug discovery: 80 years of progress

Abstract: Microbes have made a phenomenal contribution to the health and well-being of people throughout the world. In addition to producing many primary metabolites, such as amino acids, vitamins and nucleotides, they are capable of making secondary metabolites, which constitute half of the pharmaceuticals on the market today and provide agriculture with many essential products. This review centers on these beneficial secondary metabolites, the discovery of which goes back 80 years to the time when penicillin was discovered by Alexander Fleming.