Staphylococcus aureus produces autolysin-susceptible cell walls during growth in a high-NaCl and low-Ca2+ concentration medium.

Abstract

The growth of Staphylococcus aureus 209P becomes unusually sensitive to a high-NaCl concentration by decreasing the Ca2+ concentration in growth media, and cells either autolyze or transform into protoplast-like forms when grown standing in high-NaCl and low-Ca2+ concentration media below 37 C (Ochiai, T., Microbiol. Immunol. 43 (7): 705-709, 1999). To assess the role of Ca2+ in the salt tolerance of this organism, cells grown in the presence of different concentrations of Ca2+ were treated with boiling SDS, and their susceptibilities to crude autolysin (3 M LiCl extract of S. aureus 209P cells) were evaluated by turbidimetric assay and zymographic analysis. Susceptibilities of SDS-treated cells (SDS-cells) to crude autolysin were significantly influenced by Ca2+ concentration in the culture, and SDS-cells prepared from cultures grown in high-NaCl and high-Ca2+ concentration media exhibited marked resistance to crude autolysin when the assay system contained a high concentration of NaCl. On the contrary, SDS-cells prepared from cultures grown in high-NaCl and low-Ca2+ concentration media were rather susceptible to crude autolysin under the same assay conditions. A zymographic analysis revealed that the constitution of cell-associated autolysins was not influenced by the concentration of exogenous Ca2+. These results suggested that at least part of the mechanism of salt-induced autolysis in S. aureus 209P might be related to the synthesis of an autolysin susceptible cell wall.