Summary Rhizobium tropici CIAT899 has been cataloged as a nodulator of bean, a plant often growing in areas characterized by highly acidic soils. The purpose of this work was to explore the effects of acidity on the production of Nod factors by this strain and their impact on the establishment of effective symbioses. We report that acidity increases rhizobial Nod factors production, and we exhaustively study the nodulation factor structures produced under abiotic stress. Significant differences were observed between the structures produced at acid and neutral pH: 52 different molecules were produced at acid pH, 29 at neutral pH, and only 15 are common to bacteria grown at pH 7.0 or 4.5. The results indicate that R. tropici CIAT899 has successfully adapted to life in acidic soils and is a good inoculant for the bean under these conditions.