Screening Of The Strains Producing 5'-Prosphodiesterase

5'-Phosphodiesterase is a kind of phosphodiesterase, which hydrolyzes only singlest randed RNA or DNA and is mainly used for industrial production of 5'-nucleotide, widely distributed in nature, many animals, plants and microorganisms can excrete it. This paper concentrates on the screening and identification the producing 5'-Phosphodiesterase strain, the optimization of culture medium and cultivation conditions as well as the enzymatic properties of 5'-Phosphodiesterase. Main results are as follows:By a screening method with RNA as the only carbon and nitrogen resource, strain 8-1-7 was isolated from the earth and the enzyme activity of strain 8-1-7 achieved 273U/mL. Based on the colonial morphology and hyphostroma morphology of 8-1-7, the strain which was identificated to be Penicillium citrinum , designated P.citrinum ST817.After P.citrinum ST817 was treated by UV-irradiation, NTG, high temperature and DES, a strain producing 5'-Phosphodiesterase with a high yield, was successfully obtained. And the mutant strain was named P. citrinum YB-1.In this paper, the culture medium and the fermentation conditions of the strain P. citrinum YB-1 were optimized by single-factor experiment. The optimum culture conditions for enzyme production were as follows (g/L): glucose 60; peptone 6; KH₂PO₄ 0.4; K₂HPO₄ 0.6; MgSO₄·7H₂O 0.3; CaCl₂ 0.2; MnSO4 0.15, initial pH 5.5, temperature 30℃, rotation speed of rocking bed 180r/min, broth's volume in shake flask 35mL/250mL and culture time 72h. Under the optimum condition, the enzyme activity of 5'-Phosphodiesterase was enhanced from 693U/mL to 937.17U/mL. The characterization of' 5'-Phosphodiesterase from P. citrinum YB-1 was studied: the enzyme was stable between 60℃ 70℃and pH 5.5⁷.5. Its maximum enzyme activity was at 65℃,pH 5.5. The enzyme activity can be advanced by Zn²⁺ and Mn²⁺ and inhibited by Fe³⁺, Pb²⁺ and Cu²⁺.