Influence of culture medium pH and proteinase inhibitors on extracellular proteinase activity and cell growth of Sporothrix schenckii

Abstract

Sporothrix schenckii produces two extracellular proteinases in albumin- or collagen-supplemented unbuffered liquid medium. Proteinase I had an optimal pH of 6.0, and its activity was strongly inhibited by chymostatin. Proteinase II had an optimal pH of 3.5, and its activity was strongly inhibited by pepstatin. Speculating that these two proteinases are key enzymes for fungal growth, we investigated the influences of culture medium pH and either or both of the proteinase inhibitors pepstatin and chymostatin on the cell growth of S. schenckii. In buffered medium at a pH of 3.5, an optimal pH for proteinase II, only proteinase II activities were observed, while at pH 6.0, an optimal pH for proteinase I, only proteinase I activities were observed. However, there was no cell growth inhibition. These results suggested that the regulation of the production of the two proteinases is dependent on environmental pH. The addition of pepstatin or chymostatin to the culture medium did not inhibit the cell growth of S. schenckii, but the addition of both inhibitors at a concentration of 10 μg/ml strongly inhibited growth. These results suggested that at least one of the two proteinases was expressed to allow fungal growth in albumin-supplemented media. The indirect fungistatic action of the proteinase inhibitors, which inhibit proteolysis, may be applied to a topical therapeutic agent in vivo.