Priming results in faster microbial degradation of refractory organic carbon in the presence of labile organic matter, and it has been proposed to explain the disappearance of supposedly recalcitrant terrestrial organic matter that reaches the coastal ocean. We experimentally evaluated whether labile organic matter enhances the degradation of the persistent pollutants phenanthrene and pyrene (polycyclic aromatic hydrocarbons, PAH). Microcosm incubations were conducted with marine surface sediments from Concepción Bay, a PAH-impacted upwelling ecosystem in central Chile, and the Almirante Montt Gulf, a rather pristine Patagonian Fjord, resulting in enhanced degradation of phenanthrene and pyrene when microalgal and yeast extracts were added (Castillo-Ilabaca et al. 2026).  Fresh planktonic organic matter settling into sediments may serve as a primer for the degradation of recalcitrant natural and contaminant organic matter carried by rivers.  This finding, if proven in the marine environment, could help to explain the disappearance of terrestrial matter, supposedly recalcitrant, that reaches the coastal ocean and disappears.  We are currently analyzing sediment cores from the upwelling and the fjord areas and evaluating microbial decay of PAH under rain rates of predominantly fresh phytoplankton or terrestrial carbon to the sediment-water interface. 
PAH degradation during incubations evidenced a pronounced enrichment of hydrocarbonoclastic bacteria in Patagonian sediments but only a relatively modest increase in PAH-impacted sediments in Concepción Bay.  We suggest that long-term exposure to pollutants maintains a core microbiome with an enzymatic repertoire for PAH degradation, which may explain why microbial degradation is thought to remove a substantial fraction of contaminants entering the sea (e.g. González-Gaya et al 2019).

References

1. Castillo-Ilabaca C, Gerdhard L Jessen, Mario Aranda, Camila Fernández, Laurence Méjanelle, Marcelo H Gutiérrez, Silvio Pantoja-Gutiérrez.  2025. Evidence for priming-enhanced microbial degradation of polycyclic aromatic hydrocarbons in marine sediments. Marine Pollution Bulletin https://doi.org/10.1016/j.marpolbul.2025.119163
2. González-Gaya B, Martínez-Varela A, Vila-Costa M, Casal P, Cerro-Gálvez E, Berrojalbiz N, Lundin D, Vidal M, Mompeán C, Bode A, Jiménez B, Dachs J.  2019. Biodegradation as an important sink of aromatic hydrocarbons in the oceans. Nat. Geosci. https://doi.org/10.1038/s41561-018-0285-3

The study was funded by Fondecyt grant 1200252 and the Center for Oceanographic Research COPAS Coastal, ANID FB210021 (ANID-Chile). Additionally, grants REDES190106 and the CNRS International Associated Laboratory LIA MAST enabled a bioinformatics internship at the Observatoire Océanologique of Banyuls-sur-Mer in France for CCI and GLJ. CCI acknowledges Doctoral Scholarship ANID 2020 (21200707).