Purification and properties of endo-1,4-?-xylanase from Trichosporon cutaneum

Identification and characterisation of xylanolytic yeasts isolated from decaying wood and sugarcane bagasse in Brazil

In this study, yeasts associated with lignocellulosic materials in Brazil, including decaying wood and sugarcane bagasse, were isolated, and their ability to produce xylanolytic enzymes was investigated. A total of 358 yeast isolates were obtained, with 198 strains isolated from decaying wood and 160 strains isolated from decaying sugarcane bagasse samples. Seventy-five isolates possessed xylanase activity in solid medium and were identified as belonging to nine species: Candida intermedia, C. tropicalis, Meyerozyma guilliermondii, Scheffersomyces shehatae, Sugiyamaella smithiae, Cryptococcus diffluens, Cr. heveanensis, Cr. laurentii and Trichosporon mycotoxinivorans. Twenty-one isolates were further screened for total xylanase activity in liquid medium with xylan, and five xylanolytic yeasts were selected for further characterization, which included quantitative analysis of growth in xylan and xylose and xylanase and β-D-xylosidase activities. The yeasts showing the highest growth rate and cell density in xylan, Cr. laurentii UFMG-HB-48, Su. smithiae UFMG-HM-80.1 and Sc. shehatae UFMG-HM-9.1a, were, simultaneously, those exhibiting higher xylanase activity. Xylan induced the highest level of (extracellular) xylanase activity in Cr. laurentii UFMG-HB-48 and the highest level of (intracellular, extracellular and membrane-associated) β-D-xylosidase activity in Su. smithiae UFMG-HM-80.1. Also, significant β-D-xylosidase levels were detected in xylan-induced cultures of Cr. laurentii UFMG-HB-48 and Sc. shehatae UFMG-HM-9.1a, mainly in extracellular and intracellular spaces, respectively. Under xylose induction, Cr. laurentii UFMG-HB-48 showed the highest intracellular β-D-xylosidase activity among all the yeast tested. C. tropicalis UFMG-HB 93a showed its higher (intracellular) β-D-xylosidase activity under xylose induction and higher at 30 °C than at 50 °C. This study revealed different xylanolytic abilities and strategies in yeasts to metabolise xylan and/or its hydrolysis products (xylo-oligosaccharides and xylose). Xylanolytic yeasts are able to secrete xylanolytic enzymes mainly when induced by xylan and present different strategies (intra- and/or extracellular hydrolysis) for the metabolism of xylo-oligosaccharides. Some of the unique xylanolytic traits identified here should be further explored for their applicability in specific biotechnological processes.

Transfer and expression of heterologous genes in yeasts other than Saccharomyces cerevisiae

In the past few years, yeasts other than those belonging to the genus Saccharomyces have become increasingly important for industrial applications. Species such as Pichia pastoris, Hansenula polymorpha, Schizosaccharomyces pombe, Yarrowia lipolytica and Kluyveromyces lactis have been modified genetically and used for the production of heterologous proteins. For a number of additional yeasts such as Schwanniomyces occidentalis, Zygosaccharomyces rouxii, Trichosporon cutaneum, Pachysolen tannophilus, Pichia guilliermondii and members of the genus Candida genetic transformation systems have been worked out. Transformation was achieved using either dominant selection markers based on antibiotic resistance genes or auxotrophic markers in conjunction with cloned biosynthetic genes involved in amino acid or nucleotide metabolism.

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

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.

Color Variants of Aureobasidium pullulans Overproduce Xylanase with Extremely High Specific Activity

Xylanase activity from naturally occurring color variants of Aureobasidium pullulans was associated with extracellular monomeric proteins of 20 to 21 kilodaltons. Xylanase represented nearly half the total extracellular protein, with a yield of up to 0.3 g of xylanase per liter. The specific activity of partially purified xylanase exceeded 2,000 IU/mg. Xylanase from typically pigmented strains appeared similar to that from color variants with respect to molecular weight, pH and temperature optima, and specific activity of purified (but not crude) enzyme. However, xylanase from typical strains made up only about 1.0% of total extracellular protein. Xylanase from strains of Cryptococcus albidus was associated with abundant proteins of about 43 kilodaltons and showed much lower specific activity.