Résumé:
"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."
