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A stable isotope assay with 13C-labeled polyethylene to investigate plastic mineralization mediated by Rhodococcus ruber
Summary
Researchers developed a novel method using carbon-13-labeled polyethylene to precisely measure microbial plastic degradation rates. Using the bacterium Rhodococcus ruber as a model organism, they demonstrated mineralization rates of up to 1.2 percent per year for UV-treated polyethylene particles. The study establishes stable isotope tracing as a valuable tool for unambiguously proving and quantifying microbial plastic degradation.
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, 13C-labeled polyethylene (13C-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 13C from 13C-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 13C-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.