The constitutive K+ pump in Serratia marcescens

Area of Science:

• * Microbiology and cellular physiology
• * Ion transport mechanisms in bacteria

Background:

• * Serratia marcescens exhibits distinct cellular volumes and membrane potentials (delta psi) under anaerobic versus aerobic growth.
• * Respiration rates remain consistent regardless of growth conditions.

Purpose of the Study:

• * To investigate the transport of potassium (K+) and hydrogen (H+) in Serratia marcescens under varying oxygen availability.
• * To elucidate the role of membrane potential and energy sources in ion transport.

Main Methods:

• * Measurement of cellular volumes, respiration rates, and membrane potentials (delta psi).
• * Utilized inhibitors like KCN, DCCD, and CCCP to probe ion transport pathways.
• * Assessed ATP levels and K+ accumulation under different conditions, including osmotic pressure changes and glucose introduction.

Main Results:

• * Anaerobically grown cells had a larger volume (3.7 x 10(-13) cm3) than aerobically grown cells (2.4 x 10(-13) cm3).
• * Membrane potentials differed significantly: -130 mV (anaerobic) vs. -175 mV (aerobic) without external energy.
• * K+ uptake correlated with the potassium equilibrium potential and was inhibited by CCCP but not by decreased delta psi.
• * A constitutive K+ pump with a K+/ATP ratio of 2 or 3 was proposed.

Conclusions:

• * Serratia marcescens employs a constitutive K+ pump, crucial for maintaining ion homeostasis.
• * Membrane potential plays a role in K+ transport, but the pump's activity is not solely dependent on delta psi.
• * Growth conditions influence membrane potential, impacting cellular physiology.