Characterization ofAzospirillum and related diazotrophs associated with roots of plants growing in saline soils

Abstract

Diazotrophs, especially of genusAzospirillum were readily isolated from roots of many plants using semi-solid nitrogen free malate medium (NFM). These isolates formed fine, white sub-surface pellicle in nitrogen-free malate medium within 24h, which gradually moved to the surface, and exhibited high acetylene reduction rates. Using selected cultural and biochemical tests, most of the isolates were identified asAzospirillum brasilense. Four isolates from Kallar grass root surface and one isolate fromAtriplex root interior formed phenotypically a homogenous group. It shared many characteristics with the species of genusAzospirillum except shape. All the biochemical tests performed, categorized them withA. brasilense. However, the shape and the protein profile on SDS polyacrylamide gel electrophoretograms suggested that the group of these five isolates is clearly distinct and differs widely from all the type strains, belonging to various genera.