Isolation of thermophiles degrading poly(L-lactic acid)

A thermophile, strain 93, which degrades poly(L-lactic acid) (PLA) film was isolated from 144 soil samples obtained from different locations by cultivation using an enrichment culture medium at 60 degrees 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 rapidly until it reached the peak and then decreased thereafter. For residual PLA, reduced viscosity decreased rapidly but weight decreased initially slowly with a gradually increasing rate. Gel permeation chromatograms showed a marked decrease in the main peak and the appearance of a new peak in the low molecular weight region. The strain was identified as Bacillus brevis, which has an optimum growth temperature of around 58 degrees C.