Résumé
Via its ability to fix atmospheric N2, Vicia faba - rhizobia symbiosis can contribute to N inputs into crops and soil. However, symbiotic nitrogen fixation can be limited by such abiotic factors as excess of nitrogen or deficiency in phosphorus, or biotic constraint as the ineffectivity of native rhizobia. Myo-inositol hexakisphosphate (phytate) constitutes the main organic P source of soils. Phytases, the only phosphatases able to hydrolyse phytate to inorganic phosphorus, can increase P bioavailability for plants growth and development. Widely distributed among bacteria, b-propeller phytase (BPP) has been largely studied particularly among Bacillus species. Histidine acid phosphatases (HAP) represent the most studied and diverse class of phytases found among bacteria, fungi and plants. In order to search for rhizobia with phytase activity, nodule isolates from multi-location observation in an agroecosystem of south of France were screened on phytate selective medium. Among 59 isolates from V. faba nodules, 26 were able to solubilize phytate among which six identified as R. leguminosarum bv. viciae under recA gene sequencing, confirmed their ability to mineralize phytate in liquid culture. Using BPP and HAP specific primers, rhizobial isolates genes were amplified and V. faba nodules transcripts were localized in situ. It is concluded that phytate-mineralizing rhizobia exist among R. leguminosarum bv. viciae spp..