Production of induced laccase by the fungus Rhizoctonia praticola

The ability of the fungus Rhizoctonia praticola to produce an induced extracellular laccase was examined. Potential inducers, including substituted phenols, anilines, and benzoic acids, were added at a concentration of 1 mM to the growth media of fungal cultures. Of the 11 compounds tested, 5 were found to have an inductive effect. The most effective inducer, p-anisidine (p-methoxyaniline), stimulated laccase production by a factor of 30. Other parameters which influenced the production of laccase were temperature, condition of the mycelia at the time of the induction, and the concentration of the inducer. A comparison of the p-anisidine induced laccase with the constitutive laccase showed noticeable similarities in Km, pH optimum, and mobility in gel electrophoresis, suggesting that the two enzymes may be similar.

Characterization of an enzyme from Rhizoctonia praticola which polymerizes phenolic compounds

An extracellular phenol oxidase from the fungus Rhizoctonia praticola which polymerizes various xenobiotic phenols was isolated and characterized. The enzyme was purified by DEAE-cellulose and Sephadex G-200 chromatography followed by preparative polyacrylamide gel electrophoresis. Atomic absorption and EPR spectroscopy indicated the presence of copper, and SDS gel electrophoresis revealed a molecular weight of 78 000. With 2,6-dimethoxyphenol as substrate, the enzyme showed a pH optimum of 6.7–6.9, and a temperature optimum of 40 °C. According to these and additional characteristics it appears that the enzyme belongs to the class of laccases.

SURVIVAL OF SINGLE-BASIDIOSPORE ISOLATES OF RHIZOCTONIA PRATICOLA AND RHIZOCTONIA SOLANI

Twenty randomly selected single-basidiospore isolates from each of Rhizoctonia praticola and R. solani differed considerably in their tolerance to CO2, competitive saprophytic activity, and ability to survive within precolonized substrate segments incubated in soils with or without pentachloronitrobenzene (PCNB) or oat straw. With a few exceptions, isolates possessing high saprophytic activity also possessed high tolerance to CO2 and high surviving ability in precolonized substrate. Several single-spore isolates of R. solani possessed higher ability for saprophytic survival in organic matter and lower CO2-sensitivity than their parent culture. Survival of single-basidiospore isolates in precolonized substrate segments was greater in unamended soil or soil amended with oat straw than in soil treated with PCNB. Mature oat straw reduced surviving ability of several isolates, whereas it increased surviving ability of others above that observed in unamended soil. The isolates whose surviving ability was increased by oat straw were mostly those possessing high saprophytic activity in unamended soil. Saprophytic activity and virulence of all isolates tested declined with time. Rate of decline of virulence was much more rapid for weak than strong saprophytes.