Patterns of Enzymic Adaptation in Species of the Genus Azotobacter

SUMMARY: Fourteen strains of the Azotobacter agile-A. vinelandii group were classified into one or the other of the above species by morphological, cultural and growth characteristics. The groups were then surveyed by a study of oxidative reactions of whole cell suspensions on some intermediates of the tricarboxylic acid (TCA) cycle: acetate, malate, succinate, α-ketoglutarate and citrate.

All strains grew readily in a nitrogen-free medium. Organisms that were morphologically large rods or ovoid cells produced a green water-soluble pigment in an iron-deficient medium, and did not utilize mannitol or nitrate in the absence of another carbon or nitrogen source. Strains composed of smaller rods also produced the green pigment, and would utilize mannitol and nitrate. The first group was classified as Azotobacter agile, and the second as A. vinelandii.

Q O2(N)values on the TCA substrates tested did not indicate group variation. However, 15–24 hr. cells of the Azotobacter agile group as a unit did oxidize succinate with a shorter lag period (not greater than 30 min.) than strains of the A. vinelandii group (not less than 50 min.). A similar response to malate was noted, but in contrast most strains of A. vinelandii oxidized α-ketoglutarate after a shorter lag than did strains of A. agile. Citrate oxidation was variable among strains; all organisms but A. vinelandii O were apparently inhibited by the chelation of magnesium (and possibly calcium) by citrate. The physiological and oxidative responses of freshly isolated strains did not differ markedly from those of laboratory cultures of the same species.