Saline stress alters the gene expression of Azospirillum brasilense Cd

Previous studies by the authors demonstrated that the attachment of Azospir illum brasilense Cd to maize and wheat roots was altered when the bacteria were grown under saline stress. The alteration in the adsorption phase of a ttachment appeared to be related to the disappearance of a 100 kD external membrane protein in the bacterium. In this paper the effect of saline stres s on the induction of the external membrane proteins by root exudates was i nvestigated. When A. brasilense Cd was grown in an enriched medium like Lur ia broth with 300 mM NaCl added, the exudates induced the reappearance of t he 100 kD protein. If bacteria were grown in a minimal lactate medium, whea t root exudates induced the appearance of a protein of about 20 kD and an o verexpression of a 40 kD protein. Gene expression in A. brasilense was infl uenced by the presence of plant root exudates, and was dependent on the gro wing conditions. The 100 kD protein, which disappeared under saline stress, reappeared in the presence of exudates. These results may help to reveal t he importance of exudates in plant-bacteria interactions.