Bacteria include Gram positive as well as Gram negative isolates [14] and the number of new PSM species is growing.
Interestingly, Antoun et al. [15] observed that 54% of the 266 species of rhizobia obtained from the culture collections of
different laboratories were able to solubilize dicalcium phosphates. Out of 446 strains of rhizobia isolated from legume
fields in different parts of Iran, 44% were able to solubilize tricalcium phosphate and 76% mineralized inositol
hexaphosphate [16]. Therefore, if properly selected efficient strains of rhizobia compatible with AM fungi, might benefit
their plant symbiotic legumes partners, by supplying nitrogen through fixation of atmospheric N2, and by improving plant P
nutrition by mobilization of soil inorganic and organic P. Also when studying the effect of mixed inocula containing PSM
and rhizobia on legumes P-uptake, the ability of rhizobia to solubilize organic and inorganic P should be appraised.
Rhizobia have also an excellent potential to be used as PGPR and PSM with non-legume plants [10].