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.

The poly(L‐lactide) (PLA)‐degrading ability of actinomycetes obtained from culture collections was examined by the formation of clear zones on PLA‐emulsified agar plates. Using 41 genera (105 strains) of actinomycetes with phylogenetic affiliations based on 16S rRNA sequences, PLA degraders were found to be limited to members of the family Pseudonocardiaceae and related genera. They included Amycolatopsis, Saccharothrix, Lentzea, Kibdelosporangium, and Streptoalloteichus. A large number of PLA degraders were widely distributed within the genus Saccharothrix. Most strains forming clear zones on PLA‐emulsified agar plates also formed clear zones on silk fibroin agar plates. Saccharothrix species showed an ability to degrade PLA films and assimilate degradation products in liquid cultures. No significant change of the molecular weight and polydispersity (Mw/Mn) of the remaining film fragments was confirmed. After cultivation for two weeks, many irregular holes/pits on the surface of the film due to the colonization of microorganisms were observed by scanning electron microscopy.Scanning electron micrograph of the surface of PLA film: A. orientalis subsp. orientalis IFO 12362 after 14 d.magnified imageScanning electron micrograph of the surface of PLA film: A. orientalis subsp. orientalis IFO 12362 after 14 d.

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Polyester‐degrading ability of actinomycetes obtained from culture collections was investigated by the formation of clear zones on polyester‐emulsified agar plates. Using 41 genera (43 strains) of actinomycetes with phylogenetic affiliations based on 16S rRNA sequences, poly(L‐lactide) (PLA)‐degraders were found to be limited to members of family Pseudonocardiaceae and related genera. On the other hand, poly(β‐hydroxybutyrate) (PHB)‐, polycaprolactone (PCL)‐, and poly(butylene succinate) (PBS)‐degraders were widely distributed in many families.