Prospecting phosphate solubilizing bacteria in alkaline-sodic environments reveals intra-specific variability in Pantoea eucalypti affecting nutrient acquisition and rhizobial nodulation in Lotus tenuis

A bioprospecting study in alkaline-sodic soils of the Argentinean flooding pampa was performed in order to identify and characterize rhizospheric bacteria associated to Lotus tenuis plants, capable of solubilizing phosphate under a broad range of alkaline-sodic conditions. Our analysis, supported by repetitive BOX element based PCR and 16S rRNA sequences, identified 74 strains. All of them belong to the Phylum Proteobacteria, specifically to the order Enterobacteriales, and Pseudomonadales, suggesting that in this environment, broad pH-range P-solubilizing bacteria (BRPSB) associated to L. tenuis, are grouped within a narrow taxonomic range. A subsequent objective was to focus in a subgroup of BRPSB strains belonging to the Pantoea eucalypti species (MA66, P63, P76, P163, P173 and a formerly identified isolate, M91) that also produced siderophores, indol-acetic acid and showed in vitro compatibility with the native rhizobial strain Mesorhizobium sanjuanii BSA136. Growth promoting effects of these P. eucalypti strains on L. tenuis plants in alkaline-sodic soils in symbiosis with the above mentioned rhizobial strain were analyzed. Despite all the P. eucalypti BRPSB strains exhibited the above-mentioned features, they exerted differential effects on plant growth and dry matter allocation to the nodules. Plants inoculated with P. eucalypti M91 displayed a superior capability to accumulate nitrogen, phosphorus and zinc. On the contrary, nodules dry matter allocation, and mineral nutrient accumulation in L. tenuis plants were negatively affected by P. eucalypti P76 compared with M91. Results hereby presented highlight the complexity of plant-microbe interactions and reveal that growth-promoting effects of P-solubilizing P. eucalypti strains cannot be predicted only on the basis of their in vitro PGPR features, complementary in planta assays being necessary for efficient strain selection. This study provides valuable information for biofertilization of L. tenuis plants in the flooding pampa.