Biodegradation of High Density Polyethylene by Bacteria Isolated from Root Nodules of Phaseolus vulgaris

Polyethylene is one of the most inert synthetic polymers that cause long-term environmental pollution. Biodegradation, a process wherein materials are physically and chemically transformed by biological intervention, is an alternative method for waste disposal. In this study, bacteria isolated from root nodules of Phaseolus vulgaris were tested for their ability to degrade high density polyethylene (HDPE), a highly recalcitrant polymer often used as a component of packaging materials. The biodegradation process was performed for 90 days in synthetic medium containing HDPE film as the sole carbon source. Biodegradation of HDPE films was monitored by determination of dry weight of the residual polymer, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. Four bacterial isolates, phylogenetically affiliated to Pseudomonas fluorescens and Serratia marcescens, were able to reduce the weight of the residual polymer after 90 days of incubation. Isolate UPB_06, identified as Serratia marcescens, degraded up to 8% of the polyethylene film. SEM analysis revealed that the strains exhibited strong adhering capabilities as indicated by morphological changes observed on the HDPE films. The FTIR spectra showed changes in the chemical properties of the polyethylene film incubated with the bacterial isolates. Changes in the peak values of the functional groups supported the conformational change on the polymer surface. Reduction in the carbonyl index was observed in HDPE films incubated with bacterial strains suggesting biodegradation by utilization of the carbonyl residues. This study demonstrates the potential of the microorganisms for HDPE biodegradation in the absence of prior treatment such as thermal and oxidative pre-treatments.