Role of Na⁺ in growth, respiration and membrane transport in the marine bacterium Pseudomonas doudoroffii 70

Abstract

As the Na⁺ concentration in the medium was decreased below or increased above 200 to 300 mM the lag phase of growth of Pseudomonas doudoroffii 70 progressively increased in a minimal medium containing either acetate, glutamate or succinate as the carbon and energy source. At 10 mM Na⁺ the lag phase was longest with succinate, shorter with glutamate and shortest with acetate. No growth occurred without Na⁺. Maximum rates of exponential growth occurred at 20 mM and 50–100 mM Na⁺ with acetate and succinate respectively, and remained relatively constant as the Na⁺ concentration was increased to 500 mM. With glutamate, maximum rate of exponential growth occurred at 200 mM Na⁺ and decreased progressively as the Na⁺ concentration was decreased or further increased. Na⁺ was required for the transport of the substrates. Transport rates were maximum for acetate and glutamate at 200 mM Na⁺ and for succinate at 200 to 300 mM. Above and below these concentrations transport rates went down. Respiration rates with all 3 substrates were maximum at 100 mM Na⁺ and above and below this concentration the rates went down. Na⁺ concentrations corresponding to those for maximum rates of transport of the carbon source present were required to obtain the shortest lag times for growth. With acetate or succinate, rates of transport of the carbon source were not the rate limiting steps for exponential growth at the lowest Na⁺ concentrations tested. With glutamate, rates of transport limited rates of exponential growth over the whole range of Na⁺ concentrations. Evidence for active transport, Na⁺ specificity and a Na⁺ activated NADH-quinone acceptor oxidoreductase was obtained.