Currently, other PSB such as Enterobacter, Salmonella, Flavobacterium, Micrococcus, Thiobacillus, Azotobacter, Burkholderia, Enterobacteriaceae, Serratia marcescens and Baeyerlingia, are also present in the soil (Table 1) [32,33]. In addition, many different PSB were also isolated using genome sequencing (high-throughput sequencing) and raw plate isolation at different distribution sites. Table 2 and Table 3 describe the distribution of PSB by type of crop and by location, respectively.

Numerous studies have identified Bacillus spp., Pseudocystis spp. and Burkholderia spp. in different types of soils (tea gardens, saline soil, soils with heavy metals, forest soil) and in crop rhizosphere soils, where they have a high relative abundance in the bacterial community as well as a strong phosphorus-solubilizing capacity [24,25,26,27,28,29,30,

Theshoot samples were oven-dried at 105°C for half an hour to ceasemetabolic activity and then dried to a constant weight at 65°C.

The ALP activity was determined according to Tabatabai &Bremner (1969) with modification. The Olsen organic P wasdetermined using the potassium persulfate oxidation method(Schoenau & Huang, 1991):

Then, the shoot P concentration was determined according toThomas et al. (1967). The plant mycorrhizal P concentrationresponsiveness (MPCR) and mycorrhizal P content responsive-ness (MPR) were determined according to Janos (2007):

Two factors were considered in this experiment: two AM fun-gal levels, inoculation or non-inoculation of R. irregularis in theRC; three P levels, without P, with 100 mg inorganic P (in theform of KH 2 PO4 ) kg1 soil, or 100 mg nonsoluble phytate P (inthe form of phytin) kg1 soil in the HC.

5 ml of soil bacterial filtrate, which was mixed in sterile water,was added to the soil to maintain the soil bacterial community.

AMfungus used was R. irregularis

Medicago truncatula

Expression of the mps genes from Ranella aquatilis in E. coli supported a muchhigher GA production and hydroxyapatite dissolution in comparison with the donorstrain (Kim et al. 1998b), suggesting that different genetic regulation of the mpsgenes might occur in both species. MPS mutants of Pseudomonas spp. showedpleiotropic effects, with apparent involvement of regulatory mps loci in some ofthem (Krishanaraj et al. 1999). Two distinct classes of mutants namely,non-solubilizers (MPS
) and delayed expression types (MPS d ) were obtainedthrough nitrosoguanidine and Tn5 mutagenesis of Pseudomonas strain Psd 201.

Many phosphate-solubilizing bacteria includ-ing Alcaligenes, Arthrobacter, Azotobacter, Bradyrhizobium, Bacillus,Burkholderia, Chromobacterium, Enterobacter, Erwinia, Escherichia,Flavobacterium, Micrococcus, Pantoea, Pseudomonas, Salmonella, Serratia,Streptomyces, and Thiobacillus have been isolated (Zhao and Lin 2001; Sindhuet al. 2009; Castagno et al. 2011; Azziz et al. 2012). E

The most important phosphate-solubilizing bacteria belong to genera Bacillusand Pseudomonas, though species of Achromobacter, Alkaligenes, Brevibacterium,Corynebacterium, Serratia, and Xanthomonas have also been found active insolubilizing insoluble P (Venkateswarlu et al. 1984).

MPS

ficient phosphate-solubilizing fungi include the genus Aspergillus, Fusarium, Penicillium, Rhizopus,and Sclerotium (Zhao and Lin 2001). Inoculation of many phosphate-solubilizingmicroorganisms has been found to support growth of plants under nutrient imbal-ance conditions (Glick 1995; Igual et al. 2001; Wu et al. 2005)

Rahnella aquatilis

Rhizophagus intraradices