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Biodegradation of Unpretreated Low-Density Polyethylene (LDPE) by Thermophiles Isolated from Paku Hot Springs water and sendiment, Sarawak Borneo, Malaysia
Summary
Thermophilic bacteria isolated from Malaysian hot spring sediments demonstrated low-density polyethylene (LDPE) biodegradation activity over 30 days, with 7 of 96 isolates showing clear zone formation and surface hydrophobicity above 30%. Identifying thermophilic plastic-degrading microorganisms expands the toolkit for biological microplastic remediation, particularly in warm or industrial environments.
Plastic pollution has emerged as a significant environmental concern in nowadays, necessitating innovative solutions for its mitigation. Hot springs, while traditionally valued for their health and relaxation benefits, also present unique environments that may harbour thermophile bacteria species capable of degrading plastic polymers. The study aimed to screen thermophiles from Sarawak hot springs for the biodegradation of potential low-density polyethylene (LDPE) film and evaluate their efficiency in degrading the plastic in 30 days. Water and sediment samples were collected from each pond of the Paku hot spring in Sarawak Borneo, Malaysia in triplicate. The thermophiles were cultivated in an enriched medium supplemented with 0.5% (w/v) PE powder at 55°C for 5 days. Colony morphology and Gram staining were carried out. Screening of isolates for LDPE biodegradation was conducted using the BATH test, clear zone assay. Additionally, the efficiency of the isolates for 30 days of LDPE biodegradation was evaluated using the pH change, bacteria growth observation, and weight loss method. A total of 96 thermophilic isolates were cultured, 11 isolates exhibited hydrophobicity levels above 30%, and 7 isolates showed clear zone formation. After the biodegradation process, the pH was slightly decreased to pH 6.5. The bacteria colonies were Gram-positive (3) and Gram-negative (4) short rods. Isolates SPK(W)M1(1), SPK(SD)P1(2), and SPK(SD)P1(3) resulted in increased of growth (OD 0.06 ± 0.02, OD 0.08 ± 0.01, and OD 0.1 ± 0.02, respectively). The highest growth absorbance was shown by isolate SPK(SD)P1(3) while isolate SPK(W)M1(1) showed the highest LDPE film weight reduction of 10 % (0.45 ± 0.05 g). The thermophiles SPK(SD)P1(3) and SPK(W)M1(1) are potential to be used to biodegrade LDPE plastic. The preliminary study offers insight into microbial biodegradation mechanisms, further research and advanced sequencing techniques are necessary for a thorough analysis of the metabolic pathways involved.