Sodium-Dependent Growth of Azotobacter chroococcum

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 + >> NH 4 + 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 Mg 2+ was added. Li + was significantly more effective in replacing Na + than was Mg 2+ . Na + was required for growth on all C sources (glucose, sucrose, melibiose, and mannitol) and N sources (N 2 , NH 4 + , and NO 3 − ) 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.