Screening And Identification Of Phosphate-solubilizing Bacteria From Soil And Its Effects On Plant Growth

Phosphate solubilizing microorganisms is a kind of microorganisms which can transform non-soluble phosphate into available forms.It can improve the phosphorus nutrition of plants,and take an vital part in phosphorus cycling in the eco-system.After collection of 30 rhizosphere soil samples from several districts including Shijiazhuang,Xingtai,Handan and Harbin,188 phosphate-solubilizing bacteria strains were isolated on the modified selected medium using cascade dilution from these samples,among which one strain named H9 with the best ability to solubilize inorganic phosphate was further screened.The D/d ratio of strains H9 in the inorganic solid culture medium was4.4.The content of soluble phosphorus in supernatant reached up to 481.3 mg/L after cultivation of strains H9 for 120 h in liquid phosphate-solubilizing medium.According to its morphological characteristics,physiological and biochemical test and molecular biological analysis,the strain H9 was assigned to be Pseudomonas brassicacearum H9.The cultivation conditions for growth and phosphate-solubilizing ability of Pseudomonas brassicacearum H9 were optimized.The results revealed that the optimal initial pH,temperature,and aeration ratio for incubating H9 in LB medium was 7.0,28?,and 50mL/100mL,respectively.When cultivated in liquid PVK medium,the optimal temperature,pH,carbon source,and nitrogen source for phosphate solubilization was20?-37?,6-9,glucose,and?NH₄?₂SO₄ respectively.The result from seeding germination experiments indicated that treatment with a certain concentration of H9 suspension can significantly promote the germination of wheat seeds and radicle growth as well as the germination of cucumber seeds.In pot experiments using mountain area soil the results showed that H9 can significantly promote the height,leaf area,fresh weight and biomass of cucumber compared with the untreated control.Meanwhile it can increase the content of total phosphorus and available phosphorus in soil.Results from pot experiments using Vermiculite and mixed matrix?Vermiculite:Nutritional siol=1:1 v/v?revealed that H9 can significantly promote the growth of cucumber.This data indicated that H9 can promote the growth of cucumber in different soil or matrix.In order to explore the new mechanism of phosphate solubilizing,we design some related experiments.Endophytes test experiment showed that,H9 can colonization in cucumber in a period of time.Bio-assay showed that H9 can produce N-acylhomoserine lactones?AHLs?.These results laid a foundation for further theoretical study.