Studies On The Selection Of Bacterium Which Can Degrdn Polylactic Acid And Its Depolymerase

Polylactic acid(PLA)is a high polymer materials newly rising. Its physical property and chemical property is outstanding as plastic , compared with petro-chemistry plastic which is widely used and known as one of the environmental protecting materials. Polylactic acid can be degraded to harmless materia by microbion,so its perspective is absorbing . Now, polylactic acid had be used in medical domain,ecological domain and so on .The emphases of the essay are proving the feasibility of degrading polylactic acid by microorganisms, procureing a bacterium which can degrade polylactic acid in a relative short time.Such bacterium had be obtained,and its growing optimum condition had be obtained,too. Polylactic acid depolymerase has been purified and some primary analysis has been done on it.The main results obtained from the work are as follows:1.The bacterium numbered DS2006, which has the ability of degradating polylactic acid, has been purified from the mud collected from different places. The bacterium is identified as [Cellulomonas (Bergey et al.,1923),Clark]. Its growing optimum condition had be obtained. The bacterium growing in 35℃and pH=7.4 can excrete most polylactic acid depolymerase.2.Some research has been done on the polylactic acid depolymerase which is obtained from DS2006. The final purified enzyme represented the 11.25% recovery and the 14.87-fold purified protein with a activity of 1743.95 U/mg.3.The most suitable reaction temperature of this polylactic acid depolymerase is 45℃and pH is7.5. Below temperature 30℃and between pH 7.0～8.0, the enzyme is stable. Ca2+,Mg2+ can active the enzyme, but Cu2+, Hg2+ and Zn2+ will make it lose。Lactic acid (MW90) which is the monomer of PLA and dipolymer exists in the PLA degradation products.4.The bacteria DS2006 also have the ability to degrade PLA films. After nine days'degradation, PLA films partly lost their intensity and transparency. The photos by electronic scanning microscope show that the surface of the PLA films has been degraded partly.