Mesophilic anaerobic biodegradation test and analysis of eubacteria and archaea involved in anaerobic biodegradation of four specified biodegradable polyesters

Abstract

The anaerobic biodegradability of four bioplastics powders (125–250 μm), polycaprolactone (PCL), poly(lactic acid) (PLA), polyhydroxybutyrate (PHB) and poly(butylene succinate) (PBS), were compared at 37 °C under aquatic conditions using our previously reported evaluation system (the modified ISO 13975 method). The bioplastics were ranked PHB >> PLA > PCL in terms of anaerobic biodegradation rate. The biodegradability of PHB, PLA, and PCL was 90% in 9 days, 29% and 49% in 277 days, and 3% and 22% in 277 days, respectively. PBS could not be anaerobically biodegraded by the sludge used in this study. The eubacteria and archaea participating in anaerobic bioplastic biodegradation were detected using the RT-PCR DGGE method. Some eubacteria participating in anaerobic biodegradation of PCL and PLA were of unique character. Eubacteria involved in anaerobic biodegradation of PHB were 98% homologous with Arcobacter thereius, Clostridium sp, and Clostridium sp, respectively. The eubacteria involved in the anaerobic biodegradation of PLA were 100% identical to Xanthomonadaceae bacterium and Mesorhizobium sp.; however, the other three bacterium were poorly related (<95% similarity) to any of the cultured-bacterium or database sequences. Anaerobic biodegradation of PCL was conducted by eubacterium with 98% similarity to A thereius, and by five organisms with poor similarity (≤95%) to any of the cultured-bacterium or database sequences. Archaea involved in anaerobic biodegradation of PLA and PCL were 97% and 95% identical to Methanosaeta concilii and Methanobacterium petrolearium. Only faint bands were observed in the RT-PCR DGGE profile of the archaea generated during PHB anaerobic biodegradation.