Novel thermotolerant laccases produced by the white-rot fungus Physisporinus rivulosus

• Published in: Applied microbiology and biotechnology 2007-11, Vol.77 (2), p.301-309
• Main Authors: Hildén, Kristiina, Hakala, Terhi K, Maijala, Pekka, Lundell, Taina K, Hatakka, Annele
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; Carbon; Charcoal; Culture Media; Energy consumption; Enzyme kinetics; Enzyme Stability; Fundamental and applied biological sciences. Psychology; Fungi; Glucose; Hot Temperature; Industrial Microbiology - methods; Isoenzymes - biosynthesis; Kinetics; laccase; Laccase - biosynthesis; Lignin; Lignin - metabolism; Lignin degradation; Miscellaneous; Mission oriented research; Nitrogen; Oxidation; Peptones; Phenols; Physisporinus rivulosus; Picea - metabolism; Polyporaceae - enzymology; Polyporaceae - genetics; Polyporaceae - growth & development; Proteins; Sawdust; Sodium; Softwoods; Studies; Thermal activation; thermal stability; Trees; white-rot fungi; Wood - metabolism; Yeast
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-007-1155-x

The white-rot basidiomycete Physisporinus rivulosus strain T241i is highly selective for degradation of softwood lignin, which makes this fungus suitable for biopulping. In order to promote laccase production, P. rivulosus was cultivated in nutrient-nitrogen sufficient liquid media containing either charcoal or spruce sawdust as supplements. Two laccases with distinct pI values, Lac-3.5 and Lac-4.8, were purified from peptone-spruce sawdust-charcoal cultures of P. rivulosus. Both laccases showed thermal stability at up to 60°C. Lac-4.8 was thermally activated at 50°C. Surprisingly, both laccases displayed atypically low pH optima (pH 3.0-3.5) in oxidation of the commonly used laccase substrates syringaldazine (4-hydroxy-3,5-dimethoxybenzaldehyde azine), 2,6-dimethoxyphenol and guaiacol (2-methoxyphenol). Steady-state kinetic measurements pointed to unusually low affinity to guaiacol at low pH, whereas the kinetic constants for the methoxyphenols and ABTS were within the ranges reported for other fungal laccases. The combination of thermotolerance with low pH optima for methoxylated phenol substrates suggests that the two P. rivulosus T241i laccases possess potential for use in biotechnological applications.