PAH contamination in coastal surface sediments and associated bacterial communities

Polycyclic aromatic hydrocarbons (PAH) are semi-volatile, lipophilic, and harmful compounds that can persist for decades in a range of marine environments. There are several marine and soil microorganisms that possess enzymes involved in arene degradation. Here, we analyzed the structure (16S rRNA amplicons) and metabolic potential (inferred using phylogenetic placement) of the bacterial community in surface marine sediments from coastal waters off Concepción, Chile, and describe how microbial community patterns are shaped and altered by PAH contamination. Two depositional zones were identified, a "High PAH" area containing a mix of high and low molecular weight PAH of up to 10,350 ng∑PAH gdw^-1 and with high organic matter content; and a "Low PAH" zone mostly characterized by low molecular weight PAH of up to 1810 ng∑PAH gdw^-1 and lower levels of organic matter. We identified 53 hydrocarbonoclastic bacteria genera, with eight showing relatively high abundances at High PAH sites, although known PAH degrader clades were also present at Low PAH sites. With potential enzymes inferred in almost all samples, we suggest that breakdown of PAH is widespread in this area, likely resulting from the long history of local PAH emissions that may have promoted a stored microbial capacity for these degradation processes.