Extracellular protease production by submerged cultures of Schizophyllum commune

Abstract

Fungi live by secretion of hydrolytic enzymes into the growth substrate and subsequent absorption of the products of hydrolysis by the mycelium. We have investigated protease secretion by the wood-decaying basidiomycete, Schizophyllum commune, when grown submerged in a liquid minimal medium containing L-asparagine as the sole nitrogen source and in minimal medium supplemented with gelatin. The mycelia showed similar growth kinetics in both media; however, growth rates were slightly higher in the gelatin-supplemented medium. The fungus lowered the pH of both media by nearly one unit over the course of 148 h of growth and secreted measurable amounts of protein by 60 h. Proteases accumulated in both media; however, inclusion of gelatin resulted in substantially higher activity. These enzymes consisted almost entirely of serine and metallo-endoproteases and at least one diaminodipeptidase. The proportion of activity in each class, plus the absence in the medium of several mycelial proteolytic enzymes, suggests important differences in the mycelial and extracellular proteolytic systems. Gelatin-containing SDS PAGE also indicated differences in the mycelial and extracellular systems, with the extracellular system devoid of one of the major mycelial proteases involved in autolysis, S. commune Protease B—designated ScPrB. The mycelial aminopeptidase, APF, was not found in the medium, although the mycelium produced a considerable amount of this activity. Thus, these extracellular activities are likely to be secreted and not simply the result of cell breakage.

Key Words:

• basidiomycetes
• fungi
• nitrogen nutrition
• proteases