Degradation of poly(l-lactic acid) by a newly isolated thermophile

Abstract A thermophile which degrades poly( l -lactic acid) (PLA) film was isolated from 153 soil samples with an enrichment culture technique at 60 °C. Under this temperature condition, the strain grew on PLA and the dissolved total organic carbon (TOC) concentration in the medium changed according to the growth stage, i.e., after the TOC rapidly reached the minimum, it increased gradually and then decreased again thereafter. As for residual PLA, viscosity number decreased rapidly but weight decreased initially slowly. Gel permeation chromatograms of the residual PLA showed a shift of the whole peak to low molecular weight region, which suggested the occurrence of degradation to the inside of the solid sample. The strain has high specificity for PLA, and the culture broth did not show esterase activity. It was identified as a neighboring species to Geobacillus thermocatenulatus , which has an optimum growth temperature of around 60 °C.