Abstract
Background: The need for replacing conventional plastics has led to an increase of the use biodegradable plastics. Most biodegradable plastic materials are certified for compostability, and their degradation mechanisms by marine bacterial communities, is still largely unknown. Methods: Bacterial communities that degrade a PBAT-based biodegradable film (PF) were enriched from marine samples collected from the Mediterranean (Greece and Italy) and North Sea (Germany). DNA, RNA and proteins were extracted simultaneously from cultures that were starved and induced with biodegradable films, for metagenomic, transcriptomic and proteomic analyses. Mineralization of the films was assessed by CO2 evolution and film disintegration was physicochemically assessed. Results: Within the enriched marine communities, Alphaproteobacteria and Gammaproteobacteria were the most abundant classes. Among these groups, Marinobacter was the most predominant genus on the PF film. Hydrolases similar to PETases, MHETases and terephthalic acid dioxygenases, the enzymes needed for polyethylene terephthalate (PET) degradation, were expressed when communities were exposed to the biodegradable PF film. The PETases-like hydrolases (Ple) belonged to Marinobacter, MHETases-like hydrolases (Mle) to Marinobacter and Pseudooceanicola species, and the putative terephtalate dioxygenases (Tph) to Saccharospirillum and to a α-proteobacterium candidate. Ple proteins were mainly abundant and upregulated on the PF film while Mle and Tph were abundant in the free-living fraction. Around 60% of the tested biodegradable plastic was converted to CO2 and no traces of the film were detected after the mineralization was complete. Conclusion: Biodegradable plastics degradation is achieved synergistically by labour division among specialized film-attached and free-living bacteria. Ultimately, their complex interaction leads to the complete mineralization of a biodegradable plastic.
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