Selective Breeding Of Microorganism Enable To Degrade PLA And Correlated Research

Polylactide (PLA) which is used widely is one of the high polymer materials. Although PLA plastic has the same character with petro-chemistry plastic, it can be degraded by living organisms and will not lead to environmental pollution. It is known as one of the environmental protecting materials. Nowadays, PLA plays an essential role in medical science, textile industry, ecology science and daily life. PLA which has the characters of relative high melting point and high intensity is now used as a substitute of petro-chemistry plastic.The emphases of the essay are proving the feasibility of degrading PLA by microorganisms, which can degrade PLA in a relative short time. Such bacterium has been obtained, and its mutational type has been found through ultraviolet (u.v.) mutagenesis. PLA 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 DS2004, which has the ability of degradating PLA, has been purified from the mud which was discharged by No.3 Petro-Company of Fushun. DS2004-a, which has stable character of heredity, is one mutational type of DS2004 through the way of ultraviolet mutagenesis. The activity of the enzyme which is abstracted from DS2004-a is 1.1651times more than that is from DS2004.2. Some research has been done on the PLA depolymerase which is obtained from DS2004-a. The final purified enzyme represented the 10.47% recovery and the 14.67-fold purified protein with a activity of 4844.33 U/mg.3. The most suitable reaction temperature of this PLA depolymerase is 40℃and pH is 8.6. Below temperature 35℃and between pH 8.0～9.2, the enzyme is stable. Ca2+ can active the enzyme, but Cu2+, Hg2+ and Zn2+ will make it lose activation. Lactic acid (MW90) which is the monomer of PLA exists in the PLA degradation products, it combines together with H+and Na+.4. The bacteria 04-a also have the ability to degrade PLA films. After seven days'degradation, PLA films partly lost their intensity and transparency, their surface area is larger than before. The photos by electronic scanning microscope show that the surface of the PLA films has been degraded partly.