Evaluation of functional capacity and plastic-degrading potential of Bacillus spp. and other bacteria derived from the Getliņi landfill (Latvia)

The mechanisms of plastic biodegradation by microorganisms remain poorly understood because of high variability in environmental conditions. This study aimed to isolate, identify, and characterise bacteria with plastic-degrading potential derived from the Getliņi EKO landfill (Riga, Latvia). Among the bacteria selected, Bacillus was the predominant genus identified, whereas Pseudomonas dominated the metagenome. Comparative testing revealed the highest non-specific esterase activity in cultures of B. licheniformis and B. altitudinis. Following a 6-week batch experiment, a newly developed bacterial consortium biologically reduced the weight of untreated low-density polyethylene (LDPE), polyethylene terephthalate (PET), and high-density polyethylene (HDPE) by 19.44 %, 5.99 %, and 2.58 %, respectively. Thermally pre-treated PET and acid pre-treated HDPE resulted in greater weight losses than their respective untreated forms. Scanning electron microscopy primarily showed single cells and microcolonies attached to the granule surfaces. Microbial respiration and fluorescein diacetate hydrolysis tests suggested that the granules had a stimulating effect on the metabolic activity of planktonic cells. Cultures with untreated LDPE and PET exhibited the highest ecotoxicity for Thamnocephalus platyurus, reducing ingestion activity by 60.39 % and 71.25 % of the control, respectively. In conclusion, the Getliņi EKO landfill appears to be a promising sampling source for bacteria capable of biodegrading fossil-based polymers. Further refinement of methods for the isolation and evaluation of plastic degraders will provide new insights into the potential of microbial resources for plastic degradation.