Differential gene expression in Azospirillum brasilense Cd under saline stress

Previous studies in our laboratory demonstrated that the attachment of Azos pirillum brasilense Cd to maize and wheat roots was altered when the bacter ia were grown under saline stress. The aim of this work was to analyze the interaction when either the plant or both components were exposed to saline conditions. We demonstrated that this stress altered the early stages of d evelopment, in this plant model, leading to an inadequate colonization. The effect of saline stress on the expression of A. brasilense N-2 fixation ge ne promoters was also studied. While nifA expression was increased in stres sed bacteria, nifH transcription was diminished, suggesting an alteration i n the NifA activation process. The induction of the nif gene transcription by root exudates was investigated, and the results suggest that they could be modulating certain bacterial processes, such as nitrogen fixation. Howev er, stressed bacteria did not respond to the exudate's action. This could b e related to the modified membrane composition resulting from changes in pr oteins, glucans, and capsular, exo- and lipopolysaccharides. We conclude th at saline stress alters the Azospirillum brasilense Cd - maize interaction, the normal colonization, and the nitrogen fixation process.