Screening Of The Stains Producing Phosphodiesterase And The Reserch Of The Optimization Of Solid Fermentation Condition And Enzymatic Properties

Phosphodiesterases is an enzyme that can act on the phosphodiester bond of RNA or DNA to produce nucleotides deoxynucleotides.Phosphodiesterases act on the RNA are RNA enzyme,which include endonucleases and nucleicacid exonuclease depending on the modes of action.The productes of hydrolytic RNA have important applications in foods,industry,pharmaceutical,agriculture and other fields.Nucleotides and their derivatives can be used for food additives,flavorings,energy substance,coenzymes composition and so on.The experiment used RNA as the sole carbon and nitrogen source in the selective medium,a strain which produce the phosphodiesterases for 2014.49 U · g-1 of dry fermentation medium in solid fermentation which was selected from preserved in our laboratory and the soil samples and the rotting moldy fruit in several places in Guangxi.This strain is named as XD-9 and identified as Aspergillus fumigatus according to the morphological characteristics and the ITS sequence.The fermentation conditions of XD-9 optimized by the single factor experiment and orthogonal experimental design in solid fermentation:the base material is wheat bran;the culture temperature is 30?;the culture time is 3 days;the water content is 45%;the inoculation amount of 1mL spores suspension;the optimal additional carbon source is 4%of sucrose;the loading amount of a 250 mL flask is 17.5 g;the medium do not add additional nitrogen source and the metal ions.Though single factor experiments and orthogonal experimental design,the phosphodiesterases that XD-9 strain produce is about to 5783.41 U · g'1 of dry fermentation medium,which is 2.8 times higher than that before optimization of fermentation condition.The enzymatic properties for the phosphodiesterases of XD-9 strain were studied.The optimal reaction temperature is 68? and the optimum pH is 5.2.Various metal ions have different influence on enzyme activity Mg2+,Ca2+ and Mn2+ do not affect enzyme activity,while Zn2+ and Fe3+ have inhibitory effect on the enzyme activity.The inhibitory effect is small at low concentration,but as the concentration of Zn2+and Fe3+ increased,there have a very strong inhibitory effect on the enzyme activity.The stability of phosphodiesterases is well under 50 ?.When the temperature reaches 55?,the phosphodiesterases is inactivation easily.The pH stability of the phosphodiesterases is very good and it has high activity from 3 to 11.the storage stability of the phosphodiesterases is very good at room temperature,4? and-20?,the remaining activity were 90%and 80%after three months and six months,respectively.