Abstract
An actinomycete strain T16-1 demonstrated the maximum poly (L-Lactide)-degrading activity when cultured in basal liquid medium at 50°C. According to 16S rDNA sequence analysis, chemotaxonomic and DNA-DNA hybridization revealed that strain T16-1 belong to the family Thermomonosporaceae, genus Actinomadura. On the basis of phenotypic and phylogenic data, strain T16-1 which is a novel PLA-degrading thermophilic actinomycete was identified as Actinomadura keratinilytica, but the color of its colony on ISP plates, NaCl tolerant and utilization of mannitol, raffinose and arabinose were different. Partial sequence of poly (L-lactide) depolymerase gene from strain T16-1 was demonstrated. The gene consisting of 222 amino acids was related to serine protease from Streptomyces sp. with 43 to 46% identity. Key words: Actinomadura keratinilytica, cloning, identification, poly (L-lactide).
Highlights
Abundant quantities of plastic wastes are serious problems for global environment and have stimulated the improvement of biodegradable plastics
Eighty samples of surface layer soil were taken from Huai kha khaeng wildlife sanctuaries, Uthaithani province, Thailand. Among these soil samples, only samples were found active strains isolated at 50°C and 2 isolates at 40°C. This indicates that PLA-degrading microorganisms could be regarded as having a lower population in the soil as reported by Pranamuda et al (1997) and Ikura and Kudo (1999)
Beside the size of clear zone, strains T16-1, T16-4, T9-1 and T7-1 demonstrated high clearness on the plate, which could associated with the extent of their activity in culture broth
Summary
Abundant quantities of plastic wastes are serious problems for global environment and have stimulated the improvement of biodegradable plastics. (L-lactide) (PLA) aliphatic polyester is synthesized from L-lactic acid, which can be produced from farm and agricultural products such as cassava, rice, corn and corncob by fermentation methods (Miura et al, 2004; Wee et al, 2006). There has been interest in using plastic composting by microbes as a method for treating plastic waste (Tomita et al, 2003). Several thermophilic bacteria such as Bacillus brevis, Bacillus stearothermophilus and Geobacillus thermocatenulatus have been reported to possess PLAdegrading activity (Tomita et al, 1999, 2003, 2004). Unculturable microorganisms were identified from the compost consisting of PLA by using metagenomic method including Paecilomyces, Thermomonospora and Thermopolyspora (Sangwan and Wu, 2008)
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