Wheat root colonization and nitrogenase activity by Azospirillum isolates from crop plants in

Abstract: Nitrogen-fixing bacteria were isolated from the rhizosphere of different crops of Korea. A total of 16 iso-lates were selected and characterized. Thirteen of the isolates produced characteristics similar to those of the reference strains of Azospirillum, and the remaining 3 isolates were found to be Enterobacter spp. The isolates could be catego-rized into 3 groups based on their ARDRA patterns, and the first 2 groups comprised Azospirillum brasilense and Azospirillum lipoferum. The acetylene reduction activity (ARA) of these isolates was determined for free cultures and in association with wheat roots. There was no correlation between pure culture and plant-associated nitrogenase activity of the different strains. The isolates that showed higher nitrogenase activities in association with wheat roots in each group were selected and sequenced. Isolates of Azospirillum brasilense CW301, Azospirillum brasilense CW903, and Azospirillum lipoferum CW1503 were selected to study colonization in association with wheat roots. We observed higher expression of β-galactosidase activity in A. brasilense strains than in A. lipoferum strains, which could be attributed to their higher population in association with wheat roots. All strains tested colonized and exhibited the strongest β-galactosidase activity at the sites of lateral roots emergence. Key words: Azospirillum, acetylene reduction activity, 16S rDNA, ARDRA patterns, lacZ fusion. Résumé: Des bactéries fixant l’azote ont été isolées de la rhizosphère de différentes cultures de céréales en Corée. Un total de 16 isolats ont été sélectionnés et caractérisés. Treize des isolats ont produit des caractéristiques semblables