Degradation of poly(ε-caprolactone) by a thermophilic bacterium Ralstonia sp. strain MRL-TL isolated from hot spring

• PCL-degrading Ralstonia sp. strain MRL-TL was isolated from hot spring.
• A potentially new PCL depolymerase was purified and characterized from this strain.
• PCL depolymerase could degrade various polyesters besides PCL.
• Depolymerase was highly stable to various physical and chemical factors.
• Strain MRL-TL can be applied in the environment with mix plastic waste.

A thermophilic bacterium, designated as strain MRL-TL was isolated from hot water spring that could degrade poly(ε-caprolactone) (PCL). The bacterium was identified as Ralstonia sp. strain MRL-TL by 16S rRNA gene sequencing. The results of scanning electron microscopy (SEM) and fourier transform infra-red (FTIR) spectroscopy indicated the degradation of PCL by strain MRL-TL. The degradation of PCL in nature is attributed to microorganisms that secrete extracellular PCL depolymerases. PCL depolymerase was purified to homogeneity by column chromatography, as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and molecular weight was found to be approximately 50 kDa. The enzyme preferred substrate among p-nitrophenyl acyl esters was p-NP-caproate (C6), indicating that the enzyme is an esterase rather than a lipase. The enzyme was stable at 37 °C–55 °C (with an optimal temperature 50 °C) and in a pH range of 6.0–8.0 (with an optimal pH of 7.0). It was stable in the presence of various metal ions, inhibitors and surfactants. Phenylmethyl sulphonyl fluoride (PMSF) inhibited enzyme activity, which indicates that this enzyme belongs to the serine hydrolase family like other PHA depolymerases. The enzymes from MRL-TL could degrade various aliphatic polyesters; therefore, it might be applied for bioremediation in the polyesters-contaminated environments.