Hydrocarbon-Degrading Bacteria Exhibit a Species-Specific Response to Dispersed Oil while Moderating Ecotoxicity

Abstract

The Deepwater Horizon blowout in April 2010 represented the largest accidental marine oil spill and the largest release of chemical dispersants into the environment to date. While dispersant application may provide numerous benefits to oil spill response efforts, the impacts of dispersants and potential synergistic effects with crude oil on individual hydrocarbon-degrading bacteria are poorly understood. In this study, two environmentally relevant species of hydrocarbon-degrading bacteria were utilized to quantify the response to Macondo crude oil and Corexit 9500A-dispersed oil in terms of bacterial growth and oil degradation potential. In addition, specific hydrocarbon compounds were quantified in the dissolved phase of the medium and linked to ecotoxicity using a U.S. Environmental Protection Agency (EPA)-approved rotifer assay. Bacterial treatment significantly and drastically reduced the toxicity associated with dispersed oil (increasing the 50% lethal concentration [LC 50 ] by 215%). The growth and crude oil degradation potential of Acinetobacter were inhibited by Corexit by 34% and 40%, respectively; conversely, Corexit significantly enhanced the growth of Alcanivorax by 10% relative to that in undispersed oil. Furthermore, both bacterial strains were shown to grow with Corexit as the sole carbon and energy source. Hydrocarbon-degrading bacterial species demonstrate a unique response to dispersed oil compared to their response to crude oil, with potentially opposing effects on toxicity. While some species have the potential to enhance the toxicity of crude oil by producing biosurfactants, the same bacteria may reduce the toxicity associated with dispersed oil through degradation or sequestration.

Potential for Microbially Mediated Natural Attenuation of Diluted Bitumen on the Coast of British Columbia (Canada)

“…All of these ingredients have previously been shown to serve as substrates for microbial growth (14)(15)(16). The stimulation of cell growth by Corexit 9500A is therefore not surprising, and similar findings have been reported elsewhere (17)(18)(19).…”

Responses of Microbial Communities to Hydrocarbon Exposures

“…For instance, certain Colwellia taxa responded to dispersants or oil-dispersant mixtures (Baelum et al, 2012;Kleindienst et al, 2015b), while Marinobacter (Kleindienst et al, 2015b) and Acinetobacter (Overholt et al, 2016) were suppressed by dispersants. Alcanivorax borkumensis, a model obligate hydrocarbon-degrading bacterium, was shown to be negatively impacted by Corexit 9500A and all anionic dispersants (Bookstaver et al, 2015).…”

“…Alcanivorax borkumensis, a model obligate hydrocarbon-degrading bacterium, was shown to be negatively impacted by Corexit 9500A and all anionic dispersants (Bookstaver et al, 2015). Another Alcanivorax strain isolated from Macondo oil contaminated beach sands demonstrated greater oil transformation efficiency on dispersed oil, albeit with a slight lag in growth (Overholt et al, 2016).…”

Experiments and Modeling for Investigation of Oily Sludge Biodegradation in a Wastewater Pond Environment

“…Other researchers have also reported hindered dispersed oil biodegradation apparently due to the presence of a dispersant Corexit, as compared to a condition with no dispersant added, under similar 35-day batch test conditions [4]. However, this effect is not consistent with other cases [5]. The dispersants Petroclean and FFT indicated 70 to 80% biodegradation levels at 21 days of culture in shake flasks ( Table 2).…”

“…Rahsepar et al [4] applied the dispersant Corexit in testing the biodegradation of a non-weathered and a weathered crude oil and determined that the active control in which the dispersant was not included indicated a greater extent of biodegradation, as compared to the test conditions that included the dispersant. Overholt et al [5] found that the addition of the dispersant Corexit hindered the biodegradation of crude oil by the species Acinetobacter, while oil biodegradation by the species Alcanivorax was improved with the addition of Corexit. Pan et al [6] conducted experiments on oil dispersion at different mixing speeds (correlated to energy dissipation rates) and different mixing durations, and found that oil dispersion improved slightly with an increase in the mixing time.…”