Isolation and Identification of Phosphobacteria in PoplarRhizosphere from Different Regions of China

A few soil microorganisms can convert insoluble forms of phosphorus （P） to an accessible form to increase plant yields The objectives of this study were to isolate, screen and identify the phosphobacteria, i.e., phosphate-solubilizing bacteria （PSB） and phosphate-mineralizing bacteria （PMB）, in some poplar plantations and to select potential microbial inoculants that could increase the P uptake by plants. Seventy four PSB strains and 138 PMB strains were preliminarily screened from 797＂colonies isolated from the rhizosphere soil of poplar by the visible decolorization in the National Botanical Research Institute＇s phosphate growth medium （NBRIP） containing a pH indicator of bromophenol and by the clear/halo zone on yeast malt agar plate, respectively. Then, based on the solubilization of Ca3（PO4）2 in liquid NBRIP medium and the mineralization of lecithin in liquid Menkina medium, 15 PS1R strains and 7 PMB strains were further determined for their abilities to solubilize Ca3（PO4）2 and to mineralize lecithin. The results showed that the 15 PSB strains exhibited inorganic P-solubilizing abilities ranging between 376.62 and 669.56 mg L-1 and the 7 PMB strains exhibited organic P-mineralizing abilities vaxying from 0.32 to 1.56 mg L-1 three days after incubation. Three of PSB strains with the highest P-solubilizing ability, named JW-JS1, JW-JS2 and JW-SX2, were all preliminarily identified as Pseudomonas ftuorescens, while two of PMB strains with the highest P-mineralizing ability, named JYZ-SD1 and JYT-JS2, were preliminarily identified as Bacillus cereus and Bacillus subtilis, respectively. All the efficient PSB and PMB strains should be further studied under both pot culture and field conditions to test their beneficial effects on poplar.

A few soil microorganisms can convert insoluble forms of phosphorus(P) to an accessible form to increase plant yields.The objectives of this study were to isolate,screen and identify the phosphobacteria,i.e.,phosphate-solubilizing bacteria(PSB) and phosphate-mineralizing bacteria(PMB),in some poplar plantations and to select potential microbial inoculants that could increase the P uptake by plants.Seventy four PSB strains and 138 PMB strains were preliminarily screened from 797 colonies isolated from the rhizosphere soil of poplar by the visible decolorization in the National Botanical Research Institute's phosphate growth medium(NBRIP) containing a pH indicator of bromophenol and by the clear/halo zone on yeast malt agar plate,respectively.Then,based on the solubilization of Ca 3(PO 4) 2 in liquid NBRIP medium and the mineralization of lecithin in liquid Menkina medium,15 PSB strains and 7 PMB strains were further determined for their abilities to solubilize Ca 3(PO 4) 2 and to mineralize lecithin.The results showed that the 15 PSB strains exhibited inorganic P-solubilizing abilities ranging between 376.62 and 669.56 mg L -1 and the 7 PMB strains exhibited organic P-mineralizing abilities varying from 0.32 to 1.56 mg L -1 three days after incubation.Three of PSB strains with the highest P-solubilizing ability,named JW-JS1,JW-JS2 and JW-SX2,were all preliminarily identified as Pseudomonas fluorescens,while two of PMB strains with the highest P-mineralizing ability,named JYZ-SD1 and JYT-JS2,were preliminarily identified as Bacillus cereus and Bacillus subtilis,respectively.All the efficient PSB and PMB strains should be further studied under both pot culture and field conditions to test their beneficial effects on poplar.