Genome mining and screening for plastic-degrading potential in marine bacteria

Marine plastic litter, including microplastics, has a profound impact on the ocean and its wildlife, and strategies to remove/eliminate it are needed. Microbial biodegradation, particularly by bacteria, offers a potential solution, where a link between hydrocarbon and plastic-degradation has been hypothesized. This study screened the plastic-degrading potential of 18 bacterial strains isolated from 1-month-old biofilms developed in three submerged plastic fishing nets (braided polyethylene (PE), braided nylon, thin nylon). In addition, three highly efficient hydrocarbon-degrading strains were also tested. Strains were cultivated on solid minimal media with fishing net small pieces (new/unused nets) added as a carbon source for 1 month, followed by tributyrin-agar assays to assess esterase/lipase activity. Eleven bacteria exhibited enhanced growth with net polymers, mainly from the genera Sulfitobacter, Rhodococcus, Bacillus, and Pseudomonas, and eight of which bacteria also demonstrated esterase/lipase activity. Then, genes encoding hydrocarbon or plastic-degrading enzymes (alkB and almA homologs, PETase-like enzymes) were screened by PCR in the 21 mentioned bacteria and in ca.100 other strains found in submerged nets biofilm. Amplification of the investigated genes was predominantly observed in Actinomycetes strains. Genome mining of six promising strains revealed hits with enzymes linked to degradation of synthetic polymers like polyethylene terephthalate, low-density PE and nylon. The workflow developed here enabled the selection of marine bacteria with plastic-degrading potential, sourced from biofilms of submerged plastic fishing nets and hydrocarbon-enriched environments. KEY POINTS: • A comprehensive lab workflow was developed to assess plastic-degrading potential. • Genome mining in Rhodococcus and Pseudomonas strains revealed plastic-degrading enzymes. • Hydrocarbon-degrading bacteria could hold plastic-degrading capabilities.