Abstract
During the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico a deep-sea hydrocarbon plume developed resulting in a rapid succession of bacteria. Colwellia eventually supplanted Oceanospirillales, which dominated the plume early in the spill. These successional changes may have resulted, in part, from the changing composition and abundance of hydrocarbons over time. Colwellia abundance peaked when gaseous and simple aromatic hydrocarbons increased, yet the metabolic pathway used by Colwellia in hydrocarbon disposition is unknown. Here we used single-cell genomics to gain insights into the genome properties of a Colwellia enriched during the DWH deep-sea plume. A single amplified genome (SAG) of a Colwellia cell isolated from a DWH plume, closely related (avg. 98% 16S rRNA gene similarity) to other plume Colwellia, was sequenced and annotated. The SAG was similar to the sequenced isolate Colwellia psychrerythraea 34H (84% avg. nucleotide identity). Both had genes for denitrification, chemotaxis, and motility, adaptations to cold environments and a suite of nutrient acquisition genes. The Colwellia SAG may be capable of gaseous and aromatic hydrocarbon degradation, which contrasts with a DWH plume Oceanospirillales SAG which encoded non-gaseous n-alkane and cycloalkane degradation pathways. The disparate hydrocarbon degradation pathways are consistent with hydrocarbons that were abundant at different times in the deep-sea plume; first, non-gaseous n-alkanes and cycloalkanes that could be degraded by Oceanospirillales, followed by gaseous, and simple aromatic hydrocarbons that may have been degraded by Colwellia. These insights into the genomic properties of a Colwellia species, which were supported by existing metagenomic sequence data from the plume and DWH contaminated sediments, help further our understanding of the successional changes in the dominant microbial players in the plume over the course of the DWH spill.
Highlights
The Deepwater Horizon (DWH) oil spill from April to July 2010 was unprecedented due to the extreme depth (1500 m below sealevel; mbsl) and low temperature (4◦C), at which it took place
Analyses of the microbial community response to the oil spill revealed a clear story of microbial succession, few detailed descriptions of the cellular physiology of the indigenous microbes that responded to the hydrocarbon inputs have been presented
We describe several aspects of a Colwellia single-cell genome that furthers our understanding of the potential role that Colwellia played during microbial succession in the deep-sea hydrocarbon plume that formed during the DWH spill
Summary
The Deepwater Horizon (DWH) oil spill from April to July 2010 was unprecedented due to the extreme depth (1500 m below sealevel; mbsl) and low temperature (4◦C), at which it took place. Colwellia species bloomed in the deep-sea hydrocarbon plume, that formed at 1100 mbsl, in early June, 2010 (Valentine et al, 2010; Redmond and Valentine, 2012) after partial capture of the oil began (Dubinsky et al, 2013). At this time the unmitigated flow of oil ceased, and cycloalkanes and non-gaseous n-alkanes, which were dominant until that point, decreased in concentration (Dubinsky et al, 2013). The ability to degrade ethane and propane, for example, provides clues as to why Colwellia appears to have increased in abundance when the concentration of these and other gases increased in June 2010
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