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Setting new standards: Multiphasic analysis of microplastic mineralization by fungi
Summary
A tropical sooty mold fungus (Capnodium coffeae) not only grew better in the presence of polystyrene plastic than without it, but was shown using isotope-tracing techniques to actually break down and mineralize polystyrene carbon. However, the fungus assimilated only a small fraction of the plastic as biomass, suggesting plastic degradation is real but limited. This study provides rigorous new evidence for fungal plastic biodegradation and proposes improved experimental standards for confirming true plastic-degrading ability in microorganisms.
Plastic materials provide numerous benefits. However, properties such as durability and resistance to degradation that make plastic attractive for variable applications likewise foster their accumulation in the environment. Fragmentation of plastics leads to the formation of potentially hazardous microplastic, of which a considerable amount derives from polystyrene. Here, we investigated the biodegradation of polystyrene by the tropical sooty mold fungus Capnodium coffeae in different experimental setups. Growth of C. coffeae was stimulated significantly when cultured in presence of plastic polymers rather than in its absence. Stable isotope tracing using 13C-enriched polystyrene particles combined with cavity ring-down spectroscopy showed that the fungus mineralized polystyrene traces. However, phospholipid fatty acid stable isotope probing indicated only marginal assimilation of polystyrene-13C by C. coffeae in liquid cultures. NMR spectroscopic analysis of residual styrene contents prior to and after incubation revealed negligible changes in concentration. Thus, this study suggests a plastiphilic life style of C. coffeae despite minor usage of plastic as a carbon source and the general capability of sooty mold fungi to stimulate polystyrene mineralization, and proposes new standards to identify and unambiguously demonstrate plastic degrading capabilities of microbes.