Effects of soil temperature and anaerobiosis on degradation of biodegradable plastics in soil and their degrading microorganisms

The bioplastic PHB/HV (copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate) underwent a faster degradation at 30 degrees C than at 52 degrees C in soil under aerobic conditions, while there was no remarkable difference between 30 degrees C and 52 degrees C in the degradation rate of PCL [poly(epsilon-caprolactone)], PBSA (polybutylene succinate and agipate), and PBS (polybutylene succinate), PHB showed the fastest degree of degradation among the four plastics at 30 degrees C and PBSA the fastest at 52 degrees C. Degradation of all the four plastics was nor observed both at 30 degrees C and 52 degrees C under anaerobic conditions for 50 d. Microorganisms on the degrading plastics appeared to be diverse at 30 degrees C, including bacteria and fungi. However, among the several to ca. 10 kinds of bacterial and fungal strains isolated from the degradation sites of each plastic at 30 degrees C, only one or two fungal strains were able to degrade the respective plastics in vitro. The degraders were identified as Mucor sp. (PHB), Paecilomyces sp. (PCL), Aspergillus sp. (PBSA), and Cunninghamella sp. (PBSA). In contrast, only a single type of fungus was observed at the degradation sites of PCL and PBSA at 52 degrees C. The fungus isolated from PCL and PBSA was identified as Thermomyces sp. This study demonstrated that soil temperature and anaerobiosis exerted significant effects on the degradation of the plastics, and that fungi were mainly responsible for the degradation of the plastics in soil.