Study Finds Natural Sunlight Affects Oil-Degrading Bacteria Composition and Dynamics

Dr. Hernando Bacosa works at the seawater filtration system aboard the R/V Pelican 2013 cruise to the Deepwater Horizon site in the Gulf of Mexico.  Photo provided by Hernando Bacosa.

Dr. Hernando Bacosa works at the seawater filtration system aboard the R/V Pelican 2013 cruise to the Deepwater Horizon site in the Gulf of Mexico. Photo provided by Hernando Bacosa.

Scientists from the University of Texas Marine Science Institute demonstrated how natural sunlight affects Gulf of Mexico microbial communities in the presence of Corexit (dispersant) and crude oil. They observed that sunlight significantly reduced the diversity of bacterial communities in the presence of oil, Corexit, or both. While sunlight negatively affected several bacterial groups, it also preferentially selected certain bacteria. Their findings are a first to show that sunlight is a key driver for microbial community structure shifts and in determining bacterial composition and dynamics in oil-polluted surface waters. They published their results in Frontiers in Microbiology: Natural sunlight shapes crude oil-degrading bacterial communities in northern Gulf of Mexico surface waters.

Scientists have studied how oil-degrading bacterial communities interact with oil in deep Gulf of Mexico waters; however, the sea surface is a more complex environment where oil dissolution, dispersion, emulsification, evaporation, biodegradation, and photochemical degradation all occur, often simultaneously. This study’s team conducted a 36-day exposure experiment using surface water assemblages collected near the Deepwater Horizon site in May 2013. They incubated the samples under strong natural sunlight from May to July and under dark conditions while maintaining ambient water temperature to reflect conditions during the oil spill.

Using DNA extraction and pyrosequencing, the researchers analyzed bacterial communities for total abundance, density of alkane and polycyclic aromatic hydrocarbon degraders, and community composition. For treatments with oil and/or Corexit, sunlight greatly reduced the abundance of the Cyanobacterium Synechococcus but increased the relative abundances of Alteromonas, Marinobacter, Labrenzia, Sandarakinotalea, Bartonella, and Halomonas, consistent with the field observations. The study provides more details about other bacterial community responses under various treatment conditions.

The authors explained that while they did not totally account for all physical and chemical processes affecting oil fate, their findings provide important results on the evolution of the microbial communities under the influence of oil, Corexit, and sunlight. Further studies are needed to evaluate the impacts of different concentrations of crude oil and Corexit, weathered oil, and photooxidation metabolites on bacterial communities.

The study’s authors are Hernando P. Bacosa, Zhanfei Liu, and Deana L. Erdner.

This paper’s data was submitted to the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) and are available at http://data.gulfresearchinitiative.org/data/R1.x140.126:0005 (sequences) and https://data.gulfresearchinitiative.org/data/R1.x140.126:0006/ (relative abundances of bacteria genera). The data were also submitted to NCBI Sequence Read Archive (SRA) under the Accession SAMN04054215.

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This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Dispersion Research on Oil: Physics and Plankton Studies II (DROPPS II) consortium.

The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.

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