Characterization of Azomonas macrocytogenes strains isolated from Alberta soils

Abstract

Five strains of Azomonas macrocytogenes were identified from a collection of aerobic nitrogen-fixing organisms obtained from Alberta soils. The cell morphology, colony appearance, and growth conditions of these five isolates and their use of nitrogen and carbon sources were in good agreement with four standard Azomonas macrocytogenes strains. The new strains did not produce N,N,N′,N′-tetramethyl-p-phenylenediamine-dependent cytochrome oxidase, were unable to form true cysts, formed blue–white fluorescent compound(s) under iron-limited conditions, and excreted 3,4-dihydroxybenzoic acid into culture fluids. The detection of this catechol proved to be more reliable and convenient than the observation of the red–violet colour of its ferrated form, which was a variable occurrence in older cultures. Four of the new strains were antagonistic to Agrobacterium tumefaciens and two strains stimulated Erwinia carotovora growth. The new strains also demonstrated nitrogen fixation under molybdate-deficient conditions, which suggested the presence of an alternative molybdate-independent nitrogenase.