Nutrition and distribution of salt response in populations of moderately halophilic bacteria

Cultures of Micrococcus halodenitrificans and Vibrio costicolus can grow in the presence of 0.4–3.5 M NaCl. Three lines of investigation: attempts to select for more or less salt-tolerant cells; colony counts at different salt concentrations; and replica plating experiments, suggested that populations of these organisms were genetically homogeneous in their salt response. That is, each cell in a population could grow over the whole range of salt concentration in which the culture grew.The nutritional requirements of V. costicolus were studied. This organism can grow in a minimal (salts–glucose) medium at pH values above 6.0 and in a salt concentration range 0.5–2.2 M. Increasing the concentration of phosphate buffer greatly increased cell yield. The range of salt concentration in which V. costicolus could grow depended on the nutrient supply, being widest in complex media. A wider range was possible in the presence of amino acids than in a salts–glucose medium. All growth factors permitting growth to occur at high salt concentrations were not identified.