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Appl Environ Microbiol. 1986 March; 51(3): 510-514
Copyright © 1986, American Society for Microbiology. All Rights Reserved.

Sodium-Dependent Growth of Azotobacter chroococcum

Department of Microbiology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9

ABSTRACT

The majority of Azotobacter chroococcum strains in a collection obtained from Alberta soils were absolutely dependent on Na⁺ for growth. Two strains from the American Type Culture Collection also were either Na⁺ dependent or were stimulated by Na⁺. Optimal growth required 0.8 mM Na⁺ and was limited at 0.2 to 0.35 mM Na⁺. Growth promoted by 0.8 mM Na⁺ was inhibited by Rb⁺ > K⁺ >> NH₄⁺ but was not affected by Li⁺. Growth inhibition by Rb⁺ and K⁺ was overcome by increasing the Na⁺ concentration present in the medium. Excellent growth in media containing limiting Na⁺ was obtained when 25 mM Li⁺ or 25 mM Mg²⁺ was added. Li⁺ was significantly more effective in replacing Na⁺ than was Mg²⁺. Na⁺ was required for growth on all C sources (glucose, sucrose, melibiose, and mannitol) and N sources (N₂, NH₄⁺, and NO₃^–) and was required throughout the pH range of growth. Cells suspended in Na⁺ -deficient medium or in distilled water did not appear to lyse or lose viability.