Nontronite-enhanced biodegradation of Deepwater Horizon crude oil by Alcanivorax borkumensis

Laboratory experiments demonstrate that adding clay to crude oil pollution generally has a positive effect on the bacterial degradation of hydrocarbons, largely by maintaining nutrient supply. The objective of this investigation was to constrain the influence of nontronite (Fe-smectite) based clay flakes on the biodegradation of Mississippi Canyon (MC 252) crude oil from the Deepwater Horizon spill in the presence of Alcanivorax borkumensis: a dominant alkane degrader of oil pollution. Containing large amounts of Fe, dioctahedral nontronite is of particular interest as a potential source for this nutrient. Based on 37 day (888 h) long agitated batch experiments containing oil-polluted nutrient-poor seawater, the addition of nontronite clay increased the bacteria population by a factor of up to 5, reduced alkane compounds by 57.7% compared to the 45.3% reduction achieved without clay additives and stimulated the breakdown of C13-C28 molecules by oxygenase reactions. With the exception of naphthalene compounds, which were depleted largely by evaporation, a reduction in alkylated polycyclic aromatic hydrocarbons was also observed suggestive of additional biodegradation reactions. In contrast, the non-alkylated polycyclic aromatic hydrocarbons were little influenced by the presence of the clay. Although control experiments indicate that Fe2+ did not act as a limiting nutrient under the oxygenated conditions of experimentation, our results confirm that nontronite clay represents a useful amendment for enhancing the biodegradation and acts in a similar way to other smectites by sustaining nutrient supply.