Examination of the role of Na+ in the physiology of the Na+-dependent soil bacterium Azotobacter salinestris
1991
Page, W.J.
The growth of the Na+-dependent soil bacterium Azotobacter salinestris strain 184 was inhibited only 36% by 50 micromole-carbonyl cyanide m-chlorophenylhydrazone (CCCP) at alkaline pH, whereas other species of this genus were inhibited 80-90% under the same conditions. Growth of strain 184 at alkaline pH was inhibited 66% by 50 micromole-monensin and 100% by monensin plus CCCP. The majority of the AtPase activity on everted membrane vesicles prepared from strain 184 grown at alkaline pH was sensitive to azide and N,N'-dicyclohexylcarbodiimide (DCCD), but AtPase was less sensitive to these inhibitors when Na+ was present. The respiratory activity of strain 184 was neither dependent on nor activated by Na+ and was unaffected by the antagonistic Na+-analogues K+ and Rb+. A Na+-dependent, 2-heptyl-4-hydroxyquinoline N-oxide (HQNO) supersensitive NADH oxidase was not present in strain 184. Na+ was required in the growth medium to promote optimal cell yields. Limiting the amount of Na+ available caused a lag phase in which cell viability was lost. Viability was maintained by the addition of Li+ or Mg2+ to Na+-limited medium, but only Li+ appeared to promote growth. K+ appeared to be a competitive inhibitor of a Na+/Li+ site required for cell growth. Rb+ was a more complex competitor and affected the final yield and the growth rate of strain 184. Rb+-tolerant mutants of strain 184 were selected and the majority of these were found to be defective in the Na+-dependent acid excretion normally observed with A. salinestris. Analysis of an acid over-producing strain showed that Rb+ appeared to be an uncompetitive inhibitor of Na+-dependent growth and in competition with Na+ as a promoter of acidification.
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