Project description:Rhizobium tropici CIAT899 is a nodule-forming α-proteobacterium displaying intrinsic resistance to several abiotic stress conditions such as low soil pH and high temperatures, which are common in tropical environments. It is a good competitor for Phaseolus vulgaris (common bean) nodule occupancy at low pH values, however little is known about the genetic or physiological basis of acid tolerance about gene expression under acidic conditions. To identify genes responding to pH stress we studied the transcriptomes of cells grown under different pH conditions. RNA was extracted from cells grown for several generations in minimal medium at 6.8 or 4.5 (adapted cells). In addition, we acid-shocked cells pre-grown at pH 6.8 for 45 minutes at pH 4.5. Transcriptomes were determined by RNA-Seq. From a total of 6289 protein-coding genes, 383 were found to be differentially expressed under acidic conditions versus control, among which 351 were induced and 32 repressed; only 11 genes were induced upon acid shock. The acid stress response of R. tropici CIAT899 is versatile: we found genes encoding response regulators and membrane transporters, but also enzymes involved in amino acid and carbohydrate metabolism and proton extrusion. Our findings enhance our understanding of the core genes that are important during the acid stress response in R. tropici.
