Polycyclic Aromatic Hydrocarbon Degradation in the Sea-Surface Microlayer at Coastal Antarctica

As much as 400 Tg of carbon from airborne semivolatile aromatic hydrocarbons is deposited to the oceans every year, the largest identified source of anthropogenic organic carbon to the ocean. Microbial degradation is a key sink of these pollutants in surface waters, but has received little attention in polar environments. We have challenged Antarctic microbial communities from the sea-surface microlayer (SML) and the subsurface layer (SSL) with polycyclic aromatic hydrocarbons (PAHs) at environmentally relevant concentrations. PAH degradation rates and the microbial responses at both taxonomical and functional levels were assessed. Evidence for faster removal rates was observed in the SML, with rates 2.6-fold higher than in the SSL. In the SML, the highest removal rates were observed for the more hydrophobic and particle-bound PAHs. After 24 h of PAHs exposure, particle-associated bacteria in the SML showed the highest number of significant changes in their composition. These included significant enrichments of several hydrocarbonoclastic bacteria, especially the fast-growing genera Pseudoalteromonas, which increased their relative abundances by eightfold. Simultaneous metatranscriptomic analysis showed that the free-living fraction of SML was the most active fraction, especially for members of the order Alteromonadales, which includes Pseudoalteromonas. Their key role in PAHs biodegradation in polar environments should be elucidated in further studies. This study highlights the relevant role of bacterial populations inhabiting the sea-surface microlayer, especially the particle-associated habitat, as relevant bioreactors for the removal of aromatic hydrocarbons in the oceans.

Automated summary

Up to 400 million tons of carbon from airborne semivolatile aromatic hydrocarbons are deposited into the oceans annually, making it the largest known source of anthropogenic organic carbon in the ocean. Microbial degradation is an important process for removing these pollutants in surface waters, but has not been extensively studied in polar environments. This research investigates the response of Antarctic microbial communities to polycyclic aromatic hydrocarbons (PAHs) in the sea-surface microlayer (SML) and the subsurface layer (SSL). The study finds that microbial degradation rates are higher in the SML, especially for hydrophobic and particle-bound PAHs. The composition of particle-associated bacteria in the SML also significantly changes after 24 hours of PAHs exposure. This study highlights the crucial role of bacterial populations in the SML, particularly those associated with particles, in removing aromatic hydrocarbons in the oceans.