Parallel artificial and biological electric circuits power petroleum decontamination: The case of snorkel and cable bacteria

Degradation of petroleum hydrocarbons (HC) in sediments is often limited by the availability of electron acceptors. By allowing long-distance electron transport (LDET) between anoxic sediments and oxic overlying water, bioelectrochemical snorkels may stimulate the regeneration of sulphate in the anoxic sediment thereby accelerating petroleum HC degradation. Cable bacteria can also mediate LDET between anoxic and oxic sediment layers and thus theoretically stimulate petroleum HC degradation. Here, we quantitatively assessed the impact of cable bacteria and snorkels on the degradation of alkanes in marine sediment from Aarhus Bay (Denmark). After seven weeks, cable bacteria and snorkels accelerated alkanes degradation by +24 and +25%, respectively, compared to control sediment with no cable bacteria nor snorkel. The combination of snorkels and cable bacteria further enhanced alkanes degradation (+46%). Higher degradation rates were sustained by LDET-induced sulphide removal rather than, as initially hypothesized, sulphate regeneration. Cable bacteria are thus overlooked players in the self-healing capacity of crude-oil contaminated sediments, and may inspire novel remediation treatments upon hydrocarbon spillage.