Colonization and nifH expression on rice roots by Alcaligenes faecalis A15

The strain under study, Alcaligenes faecalis A15, is a diazotroph isolated from the (endo)rhizosphere of paddy rice. To study the interaction of Alcaligenes faecalis A15 with rice we have applied the gus A reporter-gene technology. With a fusion constitutively expressing the gus A gene we have analysed the colonization patterns of rice roots and the environmental factors that affect colonization. With a transcriptional fusion of the Alcaligenes faecalis A15 nifH gene and gusA we were able to visualize the expression of the nitrogen fixation genes, both in planta and in free-living conditions. Finally, we have compared nifH expression in Azospirillum brasilense, Azospirillum irakense, and Alcaligenes faecalis A15 under plant root-associated conditions.