Intensification Of Solubilization Of Insoluble Phosphate By Aspergillus Niger

The lack of phosphorus in agricultural soil is serious in China,which has become an important limiting factor of agricultural production.Microorganisms play an important role in the cycle of phosphorus in nature,and there are a large number of phosphate-solubilizing microorganisms,including bacteria and fungi,in the nature.These microorganisms can convert the insoluble phosphate to soluble phosphate,which greatly enhances the utilization of phosphate in the soil.In order to provide theoretical basis and technical support for the improving efficiency of utilizing phosphate in soil and remediation of soil,intensification of biosolubilization of insoluble phosphate by Aspergillus niger under different culture conditions was studied.The results are as follows:1.Effects of different additives on the growth and acid production of Aspergillus niger in liquid cultureThe effects of gibberellin,NAA,rutin hydrate,yeast extract and methanol on the growth of Aspergillus niger and acid production were studied.The results showed that except for methanol,the other four additives included gibberellin,NAA,rutin hydrate and yeast extract powder have a certain role in promoting the growth of Aspergillus niger,decrease of culture pH and increase of titration acid concentration under appropriate concentrations.The analysis of high performance liquid chromatography?HPLC?showed that gibberellin can promote the excretion of glucose acid and oxalic acid;NAA can promote the excretion of citric acid and oxalic acid;Rutin hydrate can promote the excretion of citric acid and oxalic acid;Yeast extract can promote the excretion of oxalic acid.Apart from NAA,gibberellin,rutin hydrate and yeast extract powder can improve the acid phosphatase activity in the culture medium.However,the neutral phosphatase and alkaline phosphatase activity were not detected.2.Effects of four additives on solubilization of insoluble phosphate by Aspergillus niger in liquid cultureTaking Ca₃?PO₄?₂,AlPO₄,FePO₄,high-phosphorus iron ore and rock phosphate as the representatives of insoluble phosphate,to study the effects of gibberellin,NAA,rutin hydrate and yeast extract powder of Aspergillus niger on the solubilization ofinsoluble phosphate.The results showed that the four additives could promote the solubilization of Ca₃?PO₄?₂,AlPO₄ and FePO₄ by Aspergillus niger under appropriate concentrations.However,the effect of rutin hydrate and yeast extract powder on the solubilization of AlPO₄ by Aspergillus niger was not obvious.The four additives could significantly promote the removal of phosphorus from high-phosphorus iron ore by Aspergillus niger.Among the four additives,the promoting effect of yeast extract was the best.Among the four additives,yeast extract could obviously promote the solubilization of rock phosphate by Aspergillus niger,while the effects of other additives were not significantly.3.Solubilization of insoluble phosphate by Aspergillus niger in solid mediumThe growth and solubilization of insoluble phosphate of Aspergillus niger in solid medium of corn meal,corn straw,wheat straw,and wheat bran were studied.The results showed that Aspergillus niger could grow well and effectively solubilize insoluble phosphate in these solid medium.The analysis result of HPLC showed that amounts of organic acids were detected,and oxalic acid was the main organic acid excreted by Aspergillus niger.The optimum conditions of solubilization of rock phosphate in different solid medium were studied.The results showed that the optimum conditions of solubilization of rock phosphate in corn straw medium were as follows: culture time 4 d,solid-liquid ratio 1:5?m:m?,dosage of rock phosphate2.0².5 g,solid medium mass 8 g.The optimum conditions of solubilization of rock phosphate in wheat straw medium were as follows: culture time 4⁵ d,solid-liquid ratio 1:4?m:m?,dosage of rock phosphate 1.5².0 g,solid medium mass 8 g.The optimum conditions of solubilization of rock phosphate in wheat bran medium were as follows: culture time 4⁵ d,solid-liquid ratio 1:2?m:m?,dosage of rock phosphate2.5 g,solid medium mass 12 g.