Abstract
Polylactic acid (PLA), a bioplastic synthesized from lactic acid, has a broad range of applications owing to its excellent proprieties such as a high melting point, good mechanical strength, transparency, and ease of fabrication. However, the safe disposal of PLA is an emerging environmental problem: it resists microbial attack in environmental conditions, and the frequency of PLA-degrading microorganisms in soil is very low. To date, a limited number of PLA-degrading bacteria have been isolated, and most are actinomycetes. In this work, a method for the selection of rare actinomycetes with extracellular proteolytic activity was established, and the technique was used to isolate four mesophilic actinomycetes with the ability to degrade emulsified PLA in agar plates. All four strains—designated SO1.1, SO1.2, SNC, and SST—belong to the genus Amycolatopsis. The PLA-degrading capability of the four strains was investigated by testing their ability to assimilate lactic acid, fragment PLA polymers, and deteriorate PLA films. The strain SNC was the best PLA degrader—it was able to assimilate lactic acid, constitutively cleave PLA, and form a thick and widespread biofilm on PLA film. The activity of this strain extensively eroded the polymer, leading to a weight loss of 36% in one month in mesophilic conditions.
Highlights
Bioplastics—biodegradable plastic materials synthesized from biomass sources—are considered an attractive alternative to conventional petroleum-based polymers, which have become one of the most serious environmental issues because of their extensive use, incorrect disposal, and non-degradability
Polylactic acid (PLA)-degrading bacteria are rare in soil [5], and most of the strains isolated to date have been rare actinomycetes mainly from the families Pseudonocardiaceae, Thermomonosporaceae, Micromonosporaceae, and Streptosporangiaceae [20] (Table 1)
The method allowed us to isolate four potential mesophilic PLA-degrading bacteria belonging to the genus Amycolatopsis
Summary
Bioplastics—biodegradable plastic materials synthesized from biomass sources—are considered an attractive alternative to conventional petroleum-based polymers, which have become one of the most serious environmental issues because of their extensive use, incorrect disposal, and non-degradability. PLA is a bioplastic with a broad range of applications because of its excellent proprieties, such as a high melting point, a high mechanical strength, a high degree of transparency, and ease of fabrication. It has been extensively used in the biomedical field as a material for sutures and bone fracture fixation, as well as for packaging materials and mulching films. The safe disposal of PLA waste is an emerging environmental problem since its biodegradation generally requires a long time, ranging from several months to years [3]. PLA biodegradation is a complex process that occurs in three phases [4]: biodeterioration, biofragmentation, and assimilation. Biodeterioration encompasses the physical and chemical modifications of PLA properties after a microbial community adheres to the material surface as a biofilm; biofragmentation is the cleavage of PLA into oligomers, dimers, or monomers by extracellular hydrolytic enzymes; assimilation involves the simple molecules resulting from biofragmentation being transported to the cytoplasm of microbial cells and catabolized
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