Isolation And Identification Of PSB And Exploration Of Their Phosphate-solubilizing Capacity And Mechanisms

Abstract：【Objective】 In order to provide resource of bacteria for screening highlyefficient and stable solubilizing strains, and then making biological bacteria agent whichcould be applied in practice activities,The author investigated phosphate-solubilizing bacteria(PSB) species and studied their ability of solubilizing fixed phosphorus in northern calcareoussoils.【Methods】Soil samples were collected from the rhizosphere of Brassica rapachinensis, Actinidia chinensis and Vitis vinifera in Yangling, Shaanxi province. The soilbacteria were isolated by dilution plate method. Then selected colonies with obviousphosphate-solubilizing zones to subculture three times continuously, The bacteria whosevalue of D/d was more than2were identified as stable and efficient PSB; Gram stain wasemployed to observe the bacteria appearance. Some physicochemical properties of each strainwere measured according to the book of Berge’s bacteria identification. The16S r DNA genesequencing and blastingwere used to identify these strains, then the author identified thesestrains’ taxonomic status. After being cultured in liquid medium，the author mixed the inoculawith calcareoussoil evenly，and then determinedinorganic phosphorusmorphology.【Results】The author achieved10PSB strains, two of them had the ability to solubilizing organicphosphorus, four strains of them could solubilize inorganic phosphorus, the other five strainshad capacity of dissolving both inorganic and organic phosphorus. the content of availablephosphorus solubilized by each strain was detected. The results showed the rang ofphosphate-dissolving ability of10strains was between1to20μg/ml(109bacteria/ml).According to the results of physicochemical properties and16s r DNA sequence analysis,1out of10strains belongs to Citrobacter youngae，another one belongs to Brevibacteriumfrigoritolerans，The other8strains are all Bacillus. Among the9strains, four of them aresimilar to Bacillus cereus; one belongs to Bacillus megaterium, one strain is Bacillusaryabhattai， two strains are Bacillus thuringiensis.After the inoculationofinorganicphosphate-solubilizingbacteria, the content of Ca8-P, Ca2-P increased, the centent ofFe-P, Al-P decreased, and the content of Ca10-P and O-Pchanged little.【Conclusion】PSB ofcalcareous soilare diversal; solubilizingcapacity ofPSBshould be measured in three ways：insolid medium, in liquid mediumand in soil; inorganicPSBin the soilcanconvert insolubleinorganic phosphorusintoavailableform orslow-releasephosphorus.Thus itsspecificsolubilizingmechanismneedsfurther study.