Isolation and Characterization of Polyester-Based Plastics-Degrading Bacteria from Compost Soils

Four potential polyester-degrading bacterial strains were isolated from compost soils in Thailand. These bacteria exhibited strong degradation activity for polyester biodegradable plastics, such as polylactic acid (PLA), polycaprolactone (PCL), poly-(butylene succinate) (PBS) and polybutylene succinate-co-adipate (PBSA) as substrates. The strains, classified according to phenotypic characteristics and 16S rDNA sequence, belonging to the genera Actinomadura, Streptomyces and Laceyella, demonstrated the best polyester- degrading activities. All strains utilized polyesters as a carbon source, and yeast extract with ammonium sulphate was utilized as a nitrogen source for enzyme production. Optimization for polyester-degrading enzyme production by Actinomadura sp. S14, Actinomadura sp. TF1, Streptomyces sp. APL3 and Laceyella sp. TP4 revealed the highest polyester-degrading activity in culture broth when 1% (w/v) PCL (18 U/mL), 0.5% (w/v) PLA (22.3 U/mL), 1% (w/v) PBS (19.4 U/mL) and 0.5% (w/v) PBSA (6.3 U/mL) were used as carbon sources, respectively. All strains exhibited the highest depolymerase activities between pH 6.0–8.0 and temperature 40–60°C. Partial nucleotides of the polyester depolymerase gene from strain S14, TF1 and APL3 were studied. We determined the amino acids making up the depolymerase enzymes had a highly conserved pentapeptide catalytic triad (Gly-His-Ser-Met-Gly), which has been shown to be part of the esterase-lipase superfamily (serine hydrolase).