Molecular Identification Of Phosphate-Solubilizing Bacteria And Characterization Of Plant Growth Promoting Activities

Plant growth promoting rhizobacteria(PGPR)are bacteria found in the rhizosphere of plants,which can enhance plant growth and healthy by various direct or indirect mechanisms.They are the significant resources for application in sustainable agriculture.Phosphate-solubilizing bacteria,one of the typical PGPR groups,are known to promote plant growth mainly by improving P availability in soils.However,their performances in soils are usually affected by various abiotic and biotic factors.Thus,the obejectives of our study are to evaluate their phosphate-solubilizing abilities under environmental stresses as well as their multiple plant growth promoting properties in vitro,thus screening for the effective inoculants for futher application in viticulture.The ten bacteria were identified using 16S rDNA amplification and sequencing techniques.Five of them(JY2,JY5,JY17,JY22,JY26)belonged to Bacillus genus;two of them(JY3,JY8)belonged to Klebsiella genus;two of them(JY10,JY15)belonged to Stenotrophomonas genus;one of them(JY11)belonged to Enterobacter genus.Based on phylogenetic tree of them and their relatives,JY2,JY17,JY22 and JY26 were clustered with type strain Bacillus aryabhattai B8W22T,while JY5 were with Bacillus megaterium IAM 13418T;JY3 and JY8 were clustered with Klebsiella variicola F2R9T;JY11 was clustered with Enterobacter aerogenes KCTC 2190T;JY10 and JY15 were clustered with Stenotrophomonas rhizophila e-p10T.The effects of various environmental stresses such as salt stress,pH stress,temperature stress,on phosphate-solublizing abilities were assayed with four high-efficient PSB,JY22,JY17,JY3 and JY8.The four strains revealed a differential response to various stress factors.Under every stress conditions,JY22 and JY17 had higher phosphate-solubilizing abilities than other two strains,JY8 and JY3.JY22 and JY17 revealed significantly higher P solubilization under 2.5%NaCl and 40℃ stressful conditions than that under non-stressful conditions.Thus,they have higher stress tolerance and can be widely applied to promote plant growth.These ten isolates were assayed for eight plant growth promoting traits,namely indole acetic acid(IAA),siderophore production,nitrogen fixation,exo-polysaccharides excretion,ACC deaminase production,hydrogen cyanide(HCN)production,chitinase as well as protease production.The results showed that all of them had multiple plant growth promoting properties,among which JY3 and JY8 displayed eight promoting potentials,thus they may become the most promising promoters for plant growth.