Lewis Otjen

Bio: Lewis Otjen is an academic researcher from University of Minnesota. The author has contributed to research in topics: Lignin & Middle lamella. The author has an hindex of 8, co-authored 9 publications receiving 521 citations. Previous affiliations of Lewis Otjen include United States Department of Agriculture.

Assessment of 30 White Rot Basidiomycetes for Selective Lignin Degradation

Abstract: Thirty wood-inhabiting basidiomycetes were screened for their ability to selectively delignify wood, The amount of lignin and carbohydrates removed and the mo hological and ultrastructural characteristics of the decayed wood were the major criteria used to determine fungi with superior lignin-degrading ability. Phellinus pini-2, Pholiota mutabilis, Phlebia brevispora-l and Phanerochaete chrysosporium were the best delignifiers of both birch and pine. Different isolates of the same species of fungi differed in both the type of decay caused and their selectivity for lignin. Almost all fungi tested caused greater weight losses in birch blocks than in pine blocks. Most fungi isolated from gymnosperms caused greater weight losses in pine than did isolates from angiosperms. The fungi studied produced two different types ofselective delignification. The first type resulted in extensive lignin removal from localized areas within wood blocks. The second type resulted in a more uniform loss throughout wood blocks, but less extensive loss from individual cell walls.

Changes in structural and chemical components of wood delignified by fungi

Abstract: Cerrena unicolor, Ganoderma applanatum, Ischnoderma resinosum and Poria medulla-panis were associated with birch wood that had been selectively delignified in the forest. Preferential lignin degradation was not uniformly distributed throughout the decayed wood. A typical white rot causing a simultaneous removal of all cell wall components was also present. In the delignified wood, 95 to 98% of the lignin was removed as well as substantial amounts of hemicelluloses. Scanning and transmission electron microscopy were used to identify the micromorphological and ultrastructural changes that occurred in the cells during degradation. In delignified areas the compound middle lamella was extensively degraded causing a defibration of cells. The secondary wall, especially the S2 layer, remained relatively unaltered. In simultaneously white-rotted wood all cell wall layers were progressively removed from the lumen toward the middle lamella causing erosion troughs or holes to form. Large voids filled with fungal mycelia resulted from a coalition of degraded areas. Birch wood decayed in laboratory soil-block tests was also intermittently delignified. Selective delignification, sparsely distributed throughout the wood, and a simultaneous rot resulting in the removal of all cell wall components were evident. Scanning electron microscopy appears to be an efficient technique for examining decayed wood for fungi with the capacity to selectively delignify wood.

A discussion of microstructural changes in wood during decomposition by white rot basidiomycetes

Abstract: The classical concepts of wood decay are reviewed. All white rot fungi do not cause the same type of cell wall decomposition. At least two micromorphologically distinct types of cell wall attack have been found. Many factors can affect the type of macroscopic and microscopic decay patterns caused by white rot basidiomycetes. Host cell type and nutrients, as well as genetic and physiologic differences among these fungi, may influence the resulting decay.

Patterns of decay caused by Inonotus dryophilus (Aphyllophorales: Hymenochaetaceae), a white-pocket rot fungus of oaks

Abstract: Decay of living white oaks (Quercus alba L. and Quercus macrocarpa Michx.) caused by the white-pocket rot fungus Inonotus (Polyporus) dryophilus (Berk.) Murr. was characterized using scanning electron and light microscopy. Delignified tissues lacked middle lamellae and degradation of the cell wall was characterized by the presence of cellulosic macrofibrils. Chemical analyses showed delignified tissues to be composed of 93.47% total sugars and 2.59% lignin, whereas sound heartwood had 64.48% total sugars and 24.99% lignin. Selective delignification occurred in axial parenchyma cells surrounding vessels of earlywood and latewood. Flame-shaped tracts of vessels with accompanying axial parenchyma, present throughout the latewood, provided avenues for radial movement of I. dryophilus. Dense groups of latewood fibers were not degraded. Inonotus dryophilus did not delignify ray parenchyma or adjacent axial parenchyma; instead, a typical white rot, differentiated microscopically by a shot-hole appearance, occurr...

Xylobolus frustulatus Decay of Oak: Patterns of Selective Delignification and Subsequent Cellulose Removal.

Abstract: Xylobolus frustulatus caused a distinct pocket rot in decorticated oak. Polymerization products appeared to accumulate in advance of delignified wood to form barriers to decay. Medullary ray parenchyma and earlywood vessels were not readily degraded and remained between pockets of decay. Chemical analyses indicated that 97% lignin, 96% xylose, and 69% mannose were removed from pockets of wood during incipient decay. Although 53% of the cellulose was removed from these areas, the remaining white tissues were composed of relatively pure cellulose. Hyphae became abundant as the released cellulose was subsequently removed. In the most advanced stages of decay, hyphae were absent from pockets, and only a sparse lining of crystals, found to contain a high concentration of calcium, remained. Images

Biodegradation of lignocellulosics: microbial, chemical, and enzymatic aspects of the fungal attack of lignin.

Abstract: Wood is the main renewable material on Earth and is largely used as building material and in paper-pulp manufacturing. This review describes the composition of lignocellulosic materials, the different processes by which fungi are able to alter wood, including decay patterns caused by white, brown, and soft-rot fungi, and fungal staining of wood. The chemical, enzymatic, and molecular aspects of the fungal attack of lignin, which represents the key step in wood decay, are also discussed. Modern analytical techniques to investigate fungal degradation and modification of the lignin polymer are reviewed, as are the different oxidative enzymes (oxidoreductases) involved in lignin degradation. These include laccases, high redox potential ligninolytic peroxidases (lignin peroxidase, manganese peroxidase, and versatile peroxidase), and oxidases. Special emphasis is given to the reactions catalyzed, their synergistic action on lignin, and the structural bases for their unique catalytic properties. Broadening our knowledge of lignocellulose biodegradation processes should contribute to better control of wood-decaying fungi, as well as to the development of new biocatalysts of industrial interest based on these organisms and their enzymes. [Int Microbiol 2005; 8(3):195-204]

Structure and Action Mechanism of Ligninolytic Enzymes

Abstract: Lignin is the most abundant renewable source of aromatic polymer in nature, and its decomposition is indispensable for carbon recycling. It is chemically recalcitrant to breakdown by most organisms because of the complex, heterogeneous structure. The white-rot fungi produce an array of extracellular oxidative enzymes that synergistically and efficiently degrade lignin. The major groups of ligninolytic enzymes include lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases. The peroxidases are heme-containing enzymes with catalytic cycles that involve the activation by H2O2 and substrate reduction of compound I and compound II intermediates. Lignin peroxidases have the unique ability to catalyze oxidative cleavage of C-C bonds and ether (C-O-C) bonds in non-phenolic aromatic substrates of high redox potential. Manganese peroxidases oxidize Mn(II) to Mn(III), which facilitates the degradation of phenolic compounds or, in turn, oxidizes a second mediator for the breakdown of non-phenolic compounds. Versatile peroxidases are hybrids of lignin peroxidase and manganese peroxidase with a bifunctional characteristic. Laccases are multi-copper-containing proteins that catalyze the oxidation of phenolic substrates with concomitant reduction of molecular oxygen to water. This review covers the chemical nature of lignin substrates and focuses on the biochemical properties, molecular structures, reaction mechanisms, and related structures/functions of these enzymes.

Microbial biodegradation of polyaromatic hydrocarbons.

Abstract: Polycyclic aromatic hydrocarbons (PAHs) are widespread in various ecosystems and are pollutants of great concern due to their potential toxicity, mutagenicity and carcinogenicity. Because of their hydrophobic nature, most PAHs bind to particulates in soil and sediments, rendering them less available for biological uptake. Microbial degradation represents the major mechanism responsible for the ecological recovery of PAH-contaminated sites. The goal of this review is to provide an outline of the current knowledge of microbial PAH catabolism. In the past decade, the genetic regulation of the pathway involved in naphthalene degradation by different gram-negative and gram-positive bacteria was studied in great detail. Based on both genomic and proteomic data, a deeper understanding of some high-molecular-weight PAH degradation pathways in bacteria was provided. The ability of nonligninolytic and ligninolytic fungi to transform or metabolize PAH pollutants has received considerable attention, and the biochemical principles underlying the degradation of PAHs were examined. In addition, this review summarizes the information known about the biochemical processes that determine the fate of the individual components of PAH mixtures in polluted ecosystems. A deeper understanding of the microorganism-mediated mechanisms of catalysis of PAHs will facilitate the development of new methods to enhance the bioremediation of PAH-contaminated sites.

Microorganisms and enzymes involved in the degradation of plant fiber cell walls

Abstract: One of natures most important biological processes is the degradation of lignocellulosic materials to carbon dioxide, water and humic substances. This implies possibilities to use biotechnology in the pulp and paper industry and consequently, the use of microorganisms and their enzymes to replace or supplement chemical methods is gaining interest. This chapter describes the structure of wood and the main wood components, cellulose, hemicelluloses and lignins. The enzyme and enzyme mechanisms used by fungi and bacteria to modify and degrade these components are described in detail. Techniques for how to assay for these enzyme activities are also described. The possibilities for biotechnology in the pulp and paper industry and other fiber utilizing industries based on these enzymes are discussed.