Towards sustainable management of plastic waste: Selection of microbial degraders and enzymes for potential application in recycling and valorization

Plastic (multilayer) packaging, which are poorly recyclable, represents most of the plastic waste that are incinerated or landfilled. Only a small fraction of plastic waste undergoes mechanical or chemical recycling, with very few studies based on enzymatic approaches. This study aimed to identify microorganisms from the Sahara Desert and their enzymes able to hydrolyze tie-layers (PBSA, PCL, PPC and PLA) and polyurethanes (PU) used as bonding component in multilayer packaging to improve their recyclability. Additionally, the study focuses on the selection of marine bacteria able to degrade polyethylene (PE) and prove bacteria-mediated mineralization using a 13C marked PE. Starting from 35 Sahara Desert isolates, three Bacillus sp. strains (L4, L81, and D.150) showed significant biodegradation, with weight losses up to 77.56±5.47% and 85.54±17.9% for PBSA and PES2b-PU, respectively. The isolate L81 exhibited the highest extracellular esterase activity (1.25±0.12 U/mL) under aerobic incubation with PBSA in rich liquid media after 48 hours incubation. L81 concentrated esterases degraded PBSA, PCL, and PUs films, with PBSA showing the highest weight loss (51.25±16.08%) and degradation rate (1.02±0.12 mg/day/cm²) within 18 hours. High 1,4-butanediol release (81.64±4.67%) was achieved after 7 days incubation with L81 indicating efficient PBSA monomerization. Moreover, marine bacteria isolated from sea water and microplastics were tested for degrading untreated plasticizers-free linear low-density PE. Bacillus sp. and Vreelandella sp. showed notable weight losses (up to 2.597±0.971%) and biofilm formation, with chemical changes confirmed by ATR-FTIR (especially for Bacillus sp.) and surface erosion by SEM. Under 13C-PE biomineralization assays, Bacillus sp. MT9 exhibit a 13C-mass loss of the added 13C-PE up to 0.184% for UV-treated 13C-PE after 60 days of incubation in liquid media added with a co-carbon source. This proves for the first time the Bacillus sp. PE mineralization abilities under lab conditions and demonstrate that plastic photodegradation supports biotic PE attack.