Screening Of Phosphorus-Solubilizing Strain And Its Phosphate Dissolving Mechanism

Phosphate-solubilizing bacteria (PSB), a group that can improve soil fertility and soil health by converting insoluble P forms to soluble forms accessible by plants, plays an important role in supplying phosphate to plants in a more environment friendly and sustainable manner to circumvent the phosphorus deficiency and benefit plant growth and development.In this thesis, phosphate-solubilizing bacteria were first screened and 49 strains were isolated from the rhizosphere soil after preliminary screening. Compared the ability of dissolving insoluble phosphate in pure liquid culture medium, PSB28 was selected as high proformance PSB with phosphoate-dissolving ability of 313.41μg/ml. Through biochemical and 16 s rDNA analysis, PSB28 was characterized as Enterobacter aerogenes.In the study of optimizing fermentation condition, we found that the optimal cultivated condition for PSB28 is at 28℃, pH7.0, in media with enough urea and fructose. Besides, PSB28 showed strong ability on dissolving calcium phosphate.In order to investigating the phosphate-dissolving mechanism of PSB28, this study assessed the phosphate solubilizing ability by comparing growth conditions inoculated in medium Ca3(PO4)2 as the sole phosphorus source with K2HPO4 as the sole phosphorus source. The results showed that after 96 h, in the case of Ca3(PO4)2 as P source, logarithmic phase was longer, but the maximum concentration of biomass was larger. The P concentration in the solution increased from 4.83μg/ml to 313.41μg/ml, when pH decreased from 7.00 to 4.61, which was higher than pH 4.12 in K2HPO4 as the sole phosphorus source. Results from HPLC-analysis showed that the strain PSB28 in the mediam Ca3(PO4)2 as P source, can secret five kinds of organic acids,which were gluconic acid, malic acid, lactic acid, acetic acid, citric acid, the highest contents of which reached to 17.66 mg/ml,8.72 mg/ml,8.56 mg/ml,5.85 mg/ml,16.78 mg/ml. Both the sorts and the quantity of organic acids in Ca3(PO4)2 medium were complicated than in K2HPO4 medium, in which only three kinds of organic aicd was detected, the corresponding highest content 0.254 mg/ml gluconic acid,0.581 mg/ml lactic acid,0.712 mg/ml acetic acid. In phosphate stress conditions, the activity of acid hosphatase was higher and both the quanlity and the sorts of organic acid were more complicated than in PSB28 slower growth rate, but slightly higher pH than the control group. It suggested that organic acids excretion by PSB28 might be the main reason for P solubilization, which may be the result of the strengthening of the TCA cycle.