Production and Ecological Significance of Yeast Cell Wall-Degrading Enzymes from Oerskovia

Abstract

Motile actinomycetes capable of degrading walls of viable yeast cells were isolated from soil and identified as Oerskovia xanthineolytica. A lytic assay based on susceptibility of enzyme-treated cells to osmotic shock was developed, and 10 of 15 strains of O. xanthineolytica, Oerskovia turbata , and nonmotile Oerskovia - like organisms from other collections were found to possess yeast lytic activities. All lytic strains produced laminaranase and α-mannanase, but the amounts, determined by reducing group assays, were not proportional to the observed lytic activities. The Oerskovia isolates demonstrated chemotactic, predatory activity against various yeast strains and killed yeasts in mixed cultures. Of 15 carbon sources tested for production of lytic enzyme, purified yeast cell walls elicited the highest activity. Glucose repressed enzyme production and caused cells to remain in the microfilamentous and motile rod stages of the Oerskovia cell cycle. Crude lytic activity was optimal at pH 5.6 to 7.0 and inactivated by heating for 6 min at 50°C. Partial purification by isoelectric focusing showed that all lytic activity was associated with four β-(1→3)-glucanases. The absence of protein disulfide reductase, N -acetyl-β- d -hexosaminidase, and phosphomannanase in crude preparations indicated that the principal enzyme responsible for yeast wall lysis was a β-(1→3)-glucanase that produced relatively little reducing sugar from yeast glucan.