Legacy and Dispersant Influence Microbial Community Dynamics in Cold Seawater Contaminated by Crude Oil Water Accommodated Fractions

Abstract

We investigated the microbial community dynamics in cold water contaminated by crude oil water accommodated fractions (WAF) prepared with or without the presence of dispersant (Finasol OSR 52). The WAFs, prepared with Naphthenic North Atlantic (NNA) crude oil, were used to contaminate seawater from Norwegian cold sites, one oil-contaminated and the other pristine. The WAF-contaminated seawaters were maintained in microcosms at 4°C for 21 days. The content of polycyclic aromatic hydrocarbons (PAH) and microbial compositions (16S rRNA gene sequencing) were determined at days 0, 7, 14 and 21. In addition, the 96 hours toxicity assay with adult Acartia tonsa revealed WAFs toxicity at days 0 and 21. The presence of dispersant in WAF increased the toxicity against Acartia tonsa but facilitated the reduction of the toxicity at day 21 without enhancing the PAH removal. The highest PAH removal was observed with the water from the oil-contaminated site revealing the legacy effect, the presence of microorganisms adapted to PAH. The PAH removal was accompanied by microbial community changes during the incubation, revealing: i) the plasticity of the microbial community to adapt to the presence of PAH and dispersant, ii) the presence of specific bacterial taxa probably involved in PAH degradation, and iii) the effects of dispersant in shaping the microbial communities dynamics through the rapid stimulation of certain potentially dispersant degrading taxa, such as Fusibacter . Thus, our results provide valuable insights on the role of microbial community in determining the fate of water solubilized hydrocarbon in cold environment questioning the role of dispersant used for fighting oil spill.

Keywords: Water Accommodated Fractions, dispersant, Cold water, Microbial communities, Bioremediation, Crude oil