Abstract
Understanding bacterial community dynamics as a result of an oil spill is important for predicting the fate of oil released to the environment and developing bioremediation strategies in the Gulf of Mexico. In this study, we aimed to elucidate the roles of temperature, water chemistry (nutrients), and initial bacterial community in selecting oil degraders through a series of incubation experiments. Surface (2 m) and bottom (1537 m) waters, collected near the Deepwater Horizon site, were amended with 200 ppm light Louisiana sweet crude oil and bacterial inoculums from surface or bottom water, and incubated at 4 or 24°C for 50 days. Bacterial community and residual oil were analyzed by pyrosequencing and gas chromatography-mass spectrometry (GC-MS), respectively. The results showed that temperature played a key role in selecting oil-degrading bacteria. Incubation at 4°C favored the development of Cycloclasticus, Pseudoalteromonas, Sulfitobacter, and Reinekea, while 24°C incubations enhanced Oleibacter, Thalassobius, Phaeobacter, and Roseobacter. Water chemistry and the initial community also had potential roles in the development of hydrocarbon-degrading bacterial communities. Pseudoalteromonas, Oleibacter, and Winogradskyella developed well in the nutrient-enriched bottom water, while Reinekea and Thalassobius were favored by low-nutrient surface water. We revealed that the combination of 4°C, crude oil and bottom inoculum was a key factor for the growth of Cycloclasticus, while the combination of surface inoculum and bottom water chemistry was important for the growth of Pseudoalteromonas. Moreover, regardless of the source of inoculum, bottom water at 24°C was a favorable condition for Oleibacter. Redundancy analysis further showed that temperature and initial community explained 57 and 19% of the variation observed, while oil and water chemistry contributed 14 and 10%, respectively. Overall, this study revealed the relative roles of temperature, water chemistry, and initial bacterial community in selecting oil degraders and regulating their evolution in the northern Gulf of Mexico.
Highlights
The exploration, production, and transportation of crude oil are expected to increase worldwide, since the crude oil demand is projected to grow 50% by 2025 (Hirsch et al, 2005)
In this study we showed that temperature profoundly affected the development of bacterial community after oil exposure in the Gulf of Mexico water
We showed that 4◦C favored the development of Cycloclasticus, Pseudoalteromonas, Sulfitobacter, and Reinekea, while 24◦C incubations enhanced Oleibacter, Thalassobius, Phaeobacter, and Roseobacter
Summary
The exploration, production, and transportation of crude oil are expected to increase worldwide, since the crude oil demand is projected to grow 50% by 2025 (Hirsch et al, 2005). Temperature fluctuation from deep water (4◦C) to sea surface (∼26◦C) and composition variations of natural gas and hydrocarbons from crude oil were attributed as the leading factors to this rapid community shift (Redmond and Valentine, 2012; Dubinsky et al, 2013) This is not surprising since temperature affects the metabolic rates of microbes including microbial growth and survival, and selects the types of bacteria that can adapt to certain temperature ranges. Some microbes such as bacteria and fungi from several cold environments have great potentials for hydrocarbon degradation at ∼0◦C (Whyte et al, 1996; Margesin et al, 2003)
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