A stable isotope assay with 13C-labeled polyethylene to investigate plastic mineralization mediated by Rhodococcus ruber

Methods that unambiguously prove microbial plastic degradation and allow for quantification of degradation rates are necessary to constrain the influence of microbial degradation on the marine plastic budget. We developed an assay based on stable isotope tracer techniques to determine microbial plastic mineralization rates in liquid medium on a lab scale. For the experiments, C-13-labeled polyethylene (C-13-PE) particles (irradiated with UV-light to mimic exposure of floating plastic to sunlight) were incubated in liquid medium with Rhodococcus ruber as a model organism for proof of principle. The transfer of C-13 from C-13-PE into the gaseous and dissolved CO2 pools translated to microbially mediated mineralization rates of up to 1.2 % yr(-1) of the added PE. After incubation, we also found highly C-13-enriched membrane fatty acids of R. ruber including compounds involved in cellular stress responses. We demonstrated that isotope tracer techniques are a valuable tool to detect and quantify microbial plastic degradation.

Automated summary

We developed an assay using stable isotope tracer techniques to determine microbial plastic mineralization rates in liquid medium on a lab scale. By incubating C-13-labeled polyethylene particles with Rhodococcus ruber as a model organism, we found that microbially mediated mineralization rates of up to 1.2% yr(-1) of the added plastic could be achieved. Isotope tracer techniques were also able to detect C-13 enrichment in membrane fatty acids of R. ruber after incubation, indicating microbial plastic degradation.