Breeding Of Cellulomonas.sp To Degrade Pla And The Research Of PLA Depolymerase

Polylactide or poly(lactic acid) (PLA) was formerly known as a hydrolyzable and unstable polyester with limited use as a biodegradable material in medical applications. Polymer processing technology has advanced quite remarkably, however, so PLA film and fiber with great stability and good physical properties are now available. Hence, the applications of PLA have expanded to include its use as a biodegradable plastic for solving the worldwide plastic waste problem.The emphases of the essay are proving the feasibility of degrading polylactic acid by microorganisms, procuring 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 DS0701, which has the ability of degradating PLA, was purified from the mud collected from different places. The bacterium is identified as [Cellulomonas (Bergey et al., 1923), Clark, 1952]. Its growing optimum condition had be obtained. The bacterium growing in 37℃and pH=7.0 can excrete most polylactic acid depolymerase.2. Some research has been done on the polylactic acid depolymerase which is obtained from DS0701, The most suitable reaction temperature of this polylactic acid depolymerase is 40℃and pH is7.0.3. The bacteria DS0701 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.4.Isolation and Purification of the enzyme, after measured of the culture conditions, the enzyme production of the strain by centrifugation, ultrafiltration, Freeze-dried, Salt precipitation, chromatography, etc. the PLA depolymerase were isolated and purified and then study the enzymatic properties of depolymerization of PLA.5. The degradation of PLA film, degradation time is 9 days, significantly decreased of transparency after degradation, to white, strength greatly reduced, and the corner of the film was turned round the corner, change crisp of the texture.