Abundance of polymers degrading microorganisms in a sea-based solid waste disposal site

In order to assess the degradability of plastics in solid waste disposal landfill sites, microbial populations capable of degrading five kinds of plastic-constituting polymers, poly epsilon-caprolactone (PCL), polylactic acid (PLA), polyethylene glycol (PEG), poly-beta-hydroxybutyrate (PHB) and cellulose acetate (CA), in a sea-based solid waste disposal site were investigated. Enumeration of aerobic and anaerobic polymers-degrading microorganisms (PDMs) was performed against to total 8 leachate samples, which were seasonally collected from the facultative pretreatment pond and the aerated lagoon. Both aerobic and anaerobic PDMs for natural polymers, PHB and CA, were found in all of the samples, while those for chemically-synthesized polymers, PCL, PLA and PEG, could not be always detected. In most cases, the ratios of the PHB- and CA-degraders to the heterotrophic bacterial population were more than 0.1%. On the other hand, the ratios of PCL-, PLA- and PEG-degraders were often much lower. These data indicate that the plastics degradation potential is commonly present in the studied disposal site, and that the degradation potential for plastics composed of chemically-synthesized polymers is inferior to that of natural polymers. Population sizes of the PDMs correlated to those of heterotrophic bacteria, and the counts of aerobic heterotrophic bacteria and PDMs in the aerated lagoon tended to be higher than those of anaerobic ones, indicating that the aeration of the leachate resulted in the activation of growth of whole aerobic microbial community including the PDMs.