Anaerobic 109Cd accumulation by cadmium-resistant and -sensitive Staphylococcus aureus

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Staphylococcus aureus exhibits varying cadmium sensitivity.
• Cadmium accumulation in bacteria is influenced by transport systems and cellular energy states.
• Understanding cadmium efflux mechanisms is crucial for microbial resistance and environmental remediation.

Purpose of the Study:

• To investigate the mechanisms of cadmium (Cd2+) accumulation and efflux in cadmium-sensitive and cadmium-resistant strains of Staphylococcus aureus.
• To elucidate the roles of membrane potential (delta psi) and proton motive force (delta pH) in cadmium transport.
• To determine the energy requirements for cadmium extrusion in S. aureus.

Main Methods:

• Utilized radiolabeled cadmium (109Cd) to quantify cellular accumulation in washed S. aureus cells under anaerobic conditions.
• Employed nigericin, a potassium ionophore, to manipulate proton motive force and assess its effect on cadmium transport.
• Varied phosphate buffer concentrations and introduced energy sources to study cadmium efflux dynamics.

Main Results:

• Cadmium-sensitive S. aureus (17810S) accumulated 109Cd via the Mn2+ porter driven by membrane potential (delta psi).
• Cadmium-resistant S. aureus (17810R) showed significantly reduced cadmium accumulation, indicating active efflux.
• Nigericin treatment modulated cadmium accumulation in strain 17810R, suggesting involvement of delta pH in cadmium extrusion, particularly at lower phosphate concentrations.
• Increased phosphate concentration and energy addition induced delta psi-dependent cadmium efflux in nigericin-pretreated resistant cells.

Conclusions:

• The Mn2+ porter facilitates cadmium uptake in S. aureus.
• Cadmium resistance in S. aureus involves an active efflux system.
• This efflux system appears to be energized by both ATP and the proton motive force (delta mu H+).