"Contribution des phytases bactériennes à l'adaptation de Phaseolus vulgaris à la faible disponibilité de phosphore en sols méditerranéens"

Abstract

"Phosphorus (P) is often one of the most limiting factors for plant growth because of its low mobility and inaccessibility in most soils, especially in the Mediterranean calcareous soils where retention of P is high. This P deficiency affects more particularly legumes because symbiotic nitrogen fixation consumes more energy than mineral assimilation. P deficiencies appear within cultures. They can be removed with inputs oh phosphate fertilizers. But this is not a renewable resource. In this context, our objectives were to isolate and characterize the functional bacterial soil community that allows mineralization of phytate, major form of organic P, in inorganic P assimilated by plants in the bean rhizosphere. The relationship between plant growth under P deficiency, the mobilization of bacteria in their rhizosphere and phytase activity were studied in the field or under controlled conditions. The density of this functional community in the rhizosphere of beans is more important in environments where P is the most limiting and phytase activity has confirmed the ability of these isolates to mineralize phytate. This functional community appears in diverse bacterial genera Pseudomonas, Pantoea, Enterobacter and Salmonella. In situ RT-PCR for gene phytase BPP showed the localization of bacteria on the roots with a strong signal on the root tip. Taken together, these results highlight the functional bacterial community mineralizing the phytate appears stimulated under condition of P deficiency. They suggest new opportunities for improving the use of organic P to P nutrition of legumes."