Characterization of a nitrogen-fixing bacterial strain from the roots of Digitaria sanguinalis

Abstract

Rates of N2 fixation of 3-10 g of N2 fixed/ha per day were associated with root systems of D. sanguinalis. A gram-negative motile aerobic bacterial strain that was capable of N2 fixation was isolated from a washed root sample of 1 of these plants. Optimal growth and N2 fixation occurred at a pH of about 6.5, a temperature of 30-37.degree. C and at a partial O2 pressure of about 0.01 atm. Increased rates of N2 fixation resulted when this strain was grown in mixed cultures with aerobic or facultative bacteria. Observations of cellular and cultural morphology and results of biochemical and physiological studies indicate that the isolate may be related to the Azotobacteriaceae but that it is not identical with any of the members of this family. The importance of N2 fixation by this isolate in nature is unknown.