Characterization of Azospirilla isolated from seeds and roots of turf grass

Abstract

Nitrogen-fixing bacteria were isolated from surface-sterilized seeds and roots of turf grasses growing in Nebraska. The percentage of successful isolations from surface-sterilized seeds ranged from 0 to 100 depending upon the source of the seeds. Based upon morphological and physiological characterization, some of the root and seed isolates appeared to be Azospirillum spp. Deoxyribonucleic acid homology studies on four selected isolates indicated that two root and one seed isolates were related to Azospirillum brasilense SP-7 with 70% or greater DNA homology, and one seed isolate was related to reference strain Azospirillum amazonense Y1 with 100% DNA homology. After repeated culturing on semisolid malate medium, some of the isolates lost their capacity to fix nitrogen. However, when certain non-nitrogen-fixing isolates were used as inoculants on turf grasses grown from surface-sterilized seeds which possessed no detectable indigenous nitrogen-fixing bacteria, nitrogenase activity as measured by acetylene reduction was detected.