Bacterial Isolation and Evaluation for Degradation of Unpretreated LDPE from Waste Dump Soils

Abstract

Plastic pollution is a universal problem, and microbial management of plastic waste represents a promising area of biotechnological research. This study investigated the ability of bacterial strains which were isolated from landfill soil to degrade Low-Density Polyethylene (LDPE). Strains obtained via serial dilution were screened for LDPE degradation on Minimal Essential Medium (MEM) with hexadecane. Nine isolates producing clearance zones on hexadecane-supplemented MEM were further tested for biofilm formation on LDPE sheets. High cell surface hydrophobicity isolates (>10%) were selected for detailed biodegradation studies. The C-8 bacterial isolate showed the highest LDPE weight loss (3.57%) and exhibited maximum laccase (0.0219 U/mL) and lipase activity (19 mm) among all bacterial isolates after 30 days. Weight loss was further validated by FTIR and SEM analysis. FTIR analysis revealed that in comparison to control, changes in peak were observed at 719 cm-1 (C-H bending), 875.67 cm-1 (C-C vibrations), 1307.07 cm-1 (C-O stretching), 1464.21 cm-1 (C-H bending), 2000-1650 cm-1 (C-H bending), 2849.85 cm-1 (C-H stretching) in microbial treated LDPE sheets. The treated LDPE also displayed increase in carbonyl index (upto 2.5 to 3 folds), double bond index (1 to 2-fold) and internal double bond index (2 to 2.5-fold) indicating oxidation and chain scission in the LDPE backbone. SEM analysis showed substantial micrometric surface damage on the LDPE film, with visible cracks and grooves. Using 16S rRNA gene sequencing, the C-8, C-11, C-15 and C-19 isolate were identified as Bacillus paramycoides, Micrococcus luteus, Bacillus siamensis and Lysinibacillus capsica, respectively.

Keywords

• ldpe
• plastic degrading enzymes
• bioremediation of plastic waste
• biodegradation of ldpe