Natural Sunlight Shapes Crude Oil-Degrading Bacterial Communities in Northern Gulf of Mexico Surface Waters

Abstract

Following the Deepwater Horizon (DWH) spill in 2010, an enormous amount of oil was observed in the deep and surface waters of the northern Gulf of Mexico. Surface waters are characterized by intense sunlight and high temperature during summer. While the oil-degrading bacterial communities in the deep-sea plume have been widely investigated, the effect of natural sunlight on those in oil polluted surface waters remains unexplored to date. In this study, we incubated surface water from the DWH site with amendments of crude oil, Corexit dispersant, or both for 36 days under natural sunlight in the northern Gulf of Mexico. The bacterial community was analyzed over time for total abundance, density of alkane and polycyclic aromatic hydrocarbon degraders, and community composition via pyrosequencing. Our results showed that, for treatments with oil and/or Corexit, sunlight significantly reduced bacterial diversity and evenness and was a key driver of shifts in bacterial community structure. In samples containing oil or dispersant, sunlight greatly reduced abundance of the Cyanobacterium Synechococcus but increased the relative abundances of Alteromonas, Marinobacter, Labrenzia, Sandarakinotalea, Bartonella, and Halomonas. Dark samples with oil were represented by members of Thalassobius, Winogradskyella, Alcanivorax, Formosa, Pseudomonas, Eubacterium, Erythrobacter, Natronocella, and Coxiella. Both oil and Corexit inhibited the Candidatus Pelagibacter with or without sunlight exposure. For the first time, we demonstrated the effects of light in structuring microbial communities in water with oil and/or Corexit. Overall, our findings improve understanding of oil pollution in surface water, and provide unequivocal evidence that sunlight is a key factor in determining bacterial community composition and dynamics in oil polluted marine waters.

Weathering of Oil Spilled in the Marine Environment

“…Incubation of seawater with oil (lightsweet crude) in sunlight resulted in changes in microbial community structure and reduced bacterial diversity (Bacosa et al, 2015). Sunlight-selected phylotypes from laboratory studies were consistent with microbial communities found in mousse from the Deepwater Horizon spill, suggesting that sunlight influences pollutant fate through impacts on microbial communities.…”

Potential Environmental Factors Affecting Oil-Degrading Bacterial Populations in Deep and Surface Waters of the Northern Gulf of Mexico

“…Cycloclasticus , a known PAH degrader (Dyksterhouse et al, 1995; Geiselbrecht et al, 1998), dominated on day 50 in 4°C incubations (35–43%), but nearly undetectable in controls and in 24°C treatments ( Figure 4B ). Alcanivorax , a known alkane degrader (Bacosa et al, 2015b, 2016), developed from undetectable to 5–7% with oil addition at both temperatures, but not in controls. In the presence of oil, Alteromonas increased from 1% initially to 4–11% on days 5 and 12 in surface water, but particularly dominated using bottom water (15–34%), suggesting the importance of water chemistry in controlling their development.…”

“…Non-metric multidimensional scaling (NMDS) was used to examine the overall patterns of bacterial community structure using Hellinger-transformed relative abundances of bacterial genera (Bacosa et al, 2015b). NMDS was performed using Bray-Curtis dissimilarity distances in PAST software package, V2.17 (Hammer et al, 2001).…”

“…In our previous work, we demonstrated the crucial role of sunlight in shaping the oil-degrading communities in the nGoM waters by incubating surface water both under the natural sunlight and in the dark (Bacosa et al, 2015b). Other environmental factors such as nutrients, and initial communites, which vary greatly from deep to surface waters, may have also contributed to the bacterial community shifts.…”

“…This knowledge is crucial in predicting fates of oil after oil spills and developing bioremediation strategies. In our recent work, we have demonstrated that solar radiation plays a key role in controlling the fate of the spilled oil and shaping the community structures of oil degraders (Bacosa et al, 2015a,b). The goal of this study is to examine the roles of temperature, nutrients, and initial bacterial community, in the biodegradation of oil and development of oil-degrading bacterial communities.…”