Saline stress alters the gene expression of Azospirillum brasilense Cd

Previous studies by the authors demonstrated that the attachment of Azospirillum brasilense Cd to maize and wheat roots was altered when the bacteria were grown under saline stress. The alteration in the adsorption phase of attachment appeared to be related to the disappearance of a 100 kD external membrane protein in the bacterium. In this paper the effect of saline stress on the induction of the external membrane proteins by root exudates was investigated. When A. brasilense Cd was grown in an enriched medium like Luria broth with 300 mM NaCl added, the exudates induced the reappearance of the 100 kD protein. If bacteria were grown in a minimal lactate medium, wheat root exudates induced the appearance of a protein of about 20 kD and an overexpression of a 40 kD protein. Gene expression in A. brasilense was influenced by the presence of plant root exudates, and was dependent on the growing conditions. The 100 kD protein, which disappeared under saline stress, reappeared in the presence of exudates. These results may help to reveal the importance of exudates in plant-bacteria interactions.