Characterization of an endo-1,3-beta-D-glucanase produced during the interaction between the mycoparasite...

The mycoparasite Stachybotrys elegans produces, in addition to a previously purified 94-kDa 1,3-beta-glucanase, at least three extracellular 1,3-beta-glucanases (75, 110, and 180 kDa) when grown on purified cell wall of Rhizoctonia solani. We purified to homogeneity an endo-1,3-beta-glucanase of 75 kDa which possesses a low K(m) value of 20 micrograms laminarin.mL-1 and is most active at pH 5.0 and 40 degrees C. Polyclonal antibodies raised against both the 75- and 94-kDa 1,3-beta-glucanases indicate that they are immunologically related but do not cross-react with the 110- and 180-kDa glucanases. Exposure of growing hyphal tips of R. solani to the pure 75-kDa 1,3-beta-glucanase caused them to swell and lyse. A transient increase of the 75-kDa 1,3-beta-glucanase with a concomitant decrease of the 94-kDa 1,3-beta-glucanase and the appearance of a 20-kDa protein were observed at the point of interaction between R. solani and Stachybotrys elegans on plates. Evidence suggesting a precursor-product relationship between the two 1,3-beta-glucanases is provided. Our results indicate that the 75-kDa 1,3-beta-glucanase may be involved in Stachybotrys elegans mycoparasitism.