BIODEGRADATION of BIOPLASTICS, INJECTED MOLDED POLYHYDROXYALKANOATES, by A BACTERIUM ISOLATED from VERMICOMPOST

ABSTRACT

According to the Argentinian Wildlife Foundation census on the coast of Buenos Aires province, 80% of the wastes were petrochemicals plastics and microplastics. Since last year, due to the influence of the COVID-19 pandemic, the use of plastics has increased, especially in containers for prepared food and single-use plastics. For this reason, the world market for bioplastics is growing steadily. The aim of this work was to evaluate the biodegradation of injected molded bioplastics in vermicompost using a bacterium isolated with extracellular enzymatic activity for the depolymerization of polyhydroxyalkanoates (PHAs). Vermicompost (Californian red worm) was sieved through 5 mm opening size. Phylogenetic analysis: the sequence of the 16S rDNA from the isolated Actinomycetes was compared with the EMBL and GenBank databases. The phylogenetic tree was constructed. The morphological characteristics were performed in ISP media and the biochemical tests were carried out according to the Bergeýs manual. Biodegradation analysis: injected molded PHAs samples consisted in rectangular (1.00 ± 0.05 cm width and 3.00 ± 0.05 cm length, thickness 200 μm) and circular samples (diameter 2 cm, thickness 0.2 cm). Biodegradation by extracellular depolymerase activity was measured at 650 nm by turbidity decrease and by halo formation around colonies (ISP media, 12 days, 30 °C). PHAs surfaces were observed using a microscope. 28 Actinomycetes were isolated with PHAs biodegradation capacity, with different types of growth, colony morphology and extracellular enzyme production. Based on the biodegradation halo area, isolates were classified into three groups low, medium and high enzymatic activity. From the last group, the one with the highest degradative activity under different environmental conditions was selected. The bacterium was identified as Streptomyces omiyaensis by phylogenetic studies, 16S rDNA sequencing, morphological characterization and biochemical tests and it was determined as GRAS. The strain was deposited in the AGRAL FAUBA culture collection as S. omiyaensis SSM5670. The PHAs samples in vermicompost inoculated with S. omiyaensis SSM5670 showed the deterioration of their surfaces, with the presence of surface irregularities and roughness, until the total biodegradation of the samples. The inoculation of vermicompost with an Actinomycetes isolate with extracellular PHAs degradation activity, would improve the bioplastics degradation, which would be critical given that the global production capacity of bioplastics has been estimated to increase to approximately 2.44 million tonnes in 2022.