Effect of Na⁺ Concentration and Nutritional Factors on the Lag Phase and Exponential Growth Rates of the Marine Bacterium Deleya aesta and of Other Marine Species

Abstract

Growth of the marine bacterium Deleya aesta in a succinate minimal medium showed increasingly long lag phases as Na⁺ was decreased below the optimum (200 to 500 mM). The minimum Na⁺ concentration permitting growth consistently was 15 mM. Supplementation of the medium with KHCO₃ (as a source of CO₂) or yeast extract, especially in combination, reduced the lag phase, increased the rate of exponential growth, and allowed growth at 8 mM Na⁺. KHCO₃ did not reduce the lag period but did increase the rate of exponential growth of Deleya venusta, Deleya pacifica, and Alteromonas haloplanktis 214. Yeast extract was active for all three. The effect of yeast extract on D. aesta could be reproduced by a mixture of amino acids approximating its amino acid composition. l-Alanine, l-aspartate, and l-methionine, in combination, were the most effective in reducing the lag phase, although not as effective as the complete mixture. Succinate, l-aspartate, and l-alanine were transported into the cells by largely independent pathways and oxidized at rates which were much lower at 10 than at 200 mM Na⁺. l-Methionine was transported at a low rate in the absence of Na⁺ and at a higher rate at 10 mM but was not oxidized. Above 25 mM Na⁺, the rate of transport of the carbon source was not the rate-limiting step for growth. It is concluded that a combination of transportable carbon sources reduced the lag period and increased the rate of exponential growth because they can be taken up independently and at low Na⁺ utilized simultaneously.

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