Biotechnology Letters 26: 771–777, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 771 Review Biodegradation of poly( L-lactide) Yutaka Tokiwa 1,∗ & Amnat Jarerat 2 1 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan 2 C.P.R. Co., Ltd., 4-102, Higashinobusue, Himeji, Hyogo 670-0965, Japan ∗ Author for correspondence (Fax: + 81-29-856-4898; E-mail: y.tokiwa@aist.go.jp) Received 9 March 2004; Accepted 9 March 2004 Key words: actinomycetes, biodegradation, polyesters, poly(L-lactide), poly(L-lactide)-degrading enzyme Abstract The biodegradation of poly(L-lactide) (PLA) is reviewed. The important role of actinomycetes in PLA degradation is emphasized. These PLA-degrading actinomycetes belong phylogenetically to the Pseudonocardiaceae family and related genera, including Amycolatopsis, Lentzea, Streptoalloteichus, Kibdelosporangium and Saccharothrix. A PLA-degrading enzyme purified from an isolated Amycolatopsis strain-41 has substrate specificity on PLA higher than proteinase K. The application of these strains and their enzymes can be effectively used for biological treatment of plastic wastes containing PLA. Introduction Serious problems regarding the treatment of plastic waste materials have stimulated the development of biodegradable plastics. Degradation of polyethylene adipate (PEA), a synthetic aliphatic polyester, was first reported by Tokiwa & Suzuki (1974). PEA was almost completely degraded by a soil fungus, Peni- cillium strain 14-3, and its purified PEA-degrading enzyme was similar to an esterase or lipase (Tokiwa & Suzuki 1977a). Further, Tokiwa & Suzuki (1977b) discovered that lipases from various microorganisms and also hog liver esterase were able to degrade syn- thetic aliphatic polyesters such as PEA and poly(ε- caprolactone) (PCL). As a result, synthetic aliphatic polyesters are now generally known to be susceptible to biological attack. The discovery of polyester de- gradation by lipase helped to extend the knowledge of plastic degradation (Tokiwa & Suzuki 1977b). Lipases obtained from Rhizopus arrhizus and hog pancreas were used to study the degradation mechanisms of aliphatic polyesters as ‘models’ of plastic degradation (Tokiwa et al. 1981, 1988). Generally, plastics are water-insoluble, solid poly- meric materials. We found that not only chemical structure but also melting temperature (Tm) affects the rate of biodegradation of plastics. The rate of de- gradation decreases with increasing the Tm (Tokiwa & Suzuki 1981). We also found that synthetic polyester degrading lipases are of two types; one dependent on the polyester Tm (e.g. R. delemar lipase) and one de- pendent on the polyester chemical structure (e.g. hog pancreas lipase) (Tokiwa et al. 1988). Various types of biodegradable polyesters are presently manufactured, such as PLA, poly(β - hydroxybutyrate) (PHB), PCL and poly(butylene suc- cinate) (PBS) (Figure 1). PHB is a natural aliphatic polyester produced by a wide variety of bacteria as an intracellular reserve of carbon and energy. On the other hand, PCL and PBS are petroleum-based poly- mers. Recently, PLA has come to be considered as a potential polymeric material due to its various advant- ages. For example, it is regarded as renewable plastic since its raw material, lactic acid, can be produced by fermentation of biomass on feedstocks including sucrose and corn and tapioca starches. It is expec- ted that PLA produced by fermentative processes will