Y. Tokiwa, and B. P. Calabia

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan

Keywords: degradation, poly(D-3-hydroxybutyrate), thermophilic, Streptomyces

The microbial polyhydroxyalkanoates (PHAs) are one of the largest groups of aliphatic polyesters that are receiving much attention as biodegradable plastics. Poly(D-3-hydroxybutyrate) (PHB) is the most ubiquitous member and most intensively studied PHA. PHB-degrading microorganisms have been found to be widely distributed in various environments. However，there is little information on microbial degradation of PHB at high temperature. Studies on thermophilic microorganisms that could degrade aliphatic polyesters will be very useful in high-temperature composting technology. A high temperature will prevent the degradation system being a breeding ground from pathogenic microorganisms.

Using the clear-zone method, we isolated a new thermophilic Streptomyces strain MG from soil which is capable of degrading PHB at 50°C. The microbial degradation of PHB films at 50°C by Streptomyces strain MG was observed using scanning electron microscopy (SEM). The formation of hemispherical holes on the films was attributable to the microbial actions of the cells attached to the films, indicating that degradation tends to occur in the colonization of PHB surface by Streptomyces sp. strain MG.  Biodegradation starts when microorganisms begin growing on the surface of the films and secrete enzymes that breakdown the polymer into molecular building blocks. This indicates that the film surfaces are favorable microhabitats for microorganisms. The PHB films were completely degraded after incubation for 6 days at 50°C.

Our isolate, Streptomyces strain MG is a good candidate for the production of pure D-3-hydroxybutyric acid which is the main component of the degradation products obtained by enzymatic degradation of PHB. A pure monomer of PHB, D-3-hydroxybutyric acid is also an important precursor of 4-acetoxyazetidinone, which is used in making carbapenem antibiotics. Intensive studies on this newfound strain as a useful microorganism for industrial application are now making progress.

论文来源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004