Microbial degradation of poly(ε-caprolactone) in a coastal environment

Abstract

Biodegradable plastics may be a solution for eliminating large marine plastic debris, such as fishing gear, which causes environmental damage. The biodegradable polyester poly(ε-caprolactone) (PCL) is degraded in various environments; however, no reports have examined PCL-degrading microbes inhabiting coastal environments, despite the fact that marine plastic debris accumulates in this environment. Therefore, in this study, we isolated a PCL-degrading bacterium (strain TKCM 64) from marine plastic debris in coastal seawater (Okinoshima Park, Chiba, Japan) for the first time. Genetic and biochemical analyses showed that strain TKCM 64 was closely related to Pseudomonas pachastrellae JCM12285T. The maximum specific growth rate (0.4 h−1) of the isolate was observed in the absence of NaCl at 30 °C, and the strain was able to grow, even at 1.20 M NaCl, suggesting that the strain could belong to a marine species showing halotolerance. Strain TKCM 64 degraded PCL film at a rate of 1.39 ± 0.09 mg cm−2·day−1. The strain showed PCL hydrolytic activity, which was induced in the presence of PCL and its hydrolysate: 6-hydroxyhexanoic acid (6HH), in addition to a major component of cutin, 16-hydroxyhexadecanoic acid. Thus, we concluded that the PCL hydrolysate 6HH, as an analog of cutin hydrolysate, functioned as an inducer of a PCL hydrolase that is a kind of cutinase in strain TKCM 64. In addition, Pseudomonas pachastrellae was found to be a key bacterial species involved in PCL degradation in coastal environments.