Isolation and Optimisation of Polylactic Acid (PLA)-packaging-degrading Actinomycete for PLA-packaging Degradation

摘要

Nowadays polylactic acid (PLA) is used extensively with respect to environmental concern and good practice in solid-waste management, as food packaging. However, the study on biodegradation of PLA-packaging is very limited. In this work, isolation, identification and optimisation of biomass production of PLA-packaging-degrading actinomycete were carried out. The isolate KKU215 gave the highest cell density in basal medium containing 1.0 g/L PLA-packaging as sole carbon source after 4-week incubation. The weight loss of PLA-packaging degraded by the isolate was 2.65%. The results from scanning electron microscopy analysis indicated that the isolate KKU215 could clearly degrade PLApackaging. The degradation of pure PLA by KKU215 as clear zone formation on emulsified PLA agar plate was observed. The 16S rDNA gene sequence of the isolate KKU215 was related to the genus Streptomyces. Thus, the isolate KKU215 was assigned as Streptomyces sp. KKU215. Concentration of yeast extract, initial pH value, temperature and agitation speed for PLA-packaging degradation were optimised by response surface methodology with Box-Behnken design. The highest growth of Streptomyces sp. KKU215 was found in basal medium with 3.26% yeast extract, initial pH value of 7.69, and agitated at 149 rpm at 33.7°C. Streptomyces sp. KKU215 when cultured in the optimal conditions could enhance PLA-packaging weight loss from 2.65% to 84.04%, which was 81.39% higher than the unoptimised conditions. Up to date, there is no report of Streptomyces species, similar with Streptomyces sp. KKU215 capable of degrading PLA. Therefore, Streptomyces sp. KKU215, a novel polylactic acid-packaging-degrading actinomycete is a promising strain for use in biodegradation of PLA-packaging.