Separable forms of nuclease secreted by Staphylococcus aureus as a function of growth stage

Abstract

The growth characteristics and nuclease secretion patterns of Staphylococcus aureus, strains UNH-15 and Foggi, were investigated. Strain Foggi grew more rapidly, but the rate of its nuclease secretion was slower than that of UNH-15. And though the terminal turbidities of both strains were about equal, the final nuclease yields of UNH-15 were 15–20% higher than Foggi's.Three chromatographically and electrophoretically separable forms of nuclease were present in the culture supernatants of these strains. Designated nucleases I, II, and III, in order of their elution from carboxymethylcellulose columns, the forms were not produced simultaneously and their relative concentrations changed during the growth cycle. During the log phase growth, I and II were produced. Near the end of this phase, III began to appear, while I and II were concurrently disappearing from the culture. Only III was present in the supernatant fluid of stationary phase cultures.Molecular sieving of the forms in G-75 Sephadex and electrophoresis in SDS-polyacrylamide indicated that the molecular weights of the I, II, and III forms were about 7 000, 14 000, and 20 000 respectively. Commercially available micrococcal nuclease appears to be electrophoretically identical with a mixture of forms II and III.