Archaeal Lipids and 16S rRNA Genes Characterizing Non-hydrate and Hydrate-Impacted Sediments in the Gulf of Mexico

Abstract

Abstract This study reports the intact lipids and the phylogenetic compositions of archaea from marine sediments adjacent to or within a region of methane seeps and hydrate mounds in the Mississippi Canyon (MC) Block 118 in the Gulf of Mexico. An aliquot of lyophilized sediment (∼5 g) was extracted for total lipids. Fractions of the glycerol dialkyl glycerol tetraethers (GDGTs) were obtained through column fractionation and determined using liquid-chromatography-mass spectrometry. DNA was extracted from a different aliquot of the sample (∼7 g) that was kept at −80°C. GDGTs showed distinct patterns between non-hydrate and hydrate-impacted samples, suggesting dramatically different archaeal communities caused by the presence of gas hydrates or cold seeps. Clone libraries of 16S rRNA genes were constructed to provide a phylogenetic explanation of the archaeal populations possibly causing the variation in lipid profiles. In contrast to the non-thermophilic crenarchaeota-dominant species in the normal marine sediment, the hydrate-impacted samples showed the predominance of ANME-1 subgroups with Thermoplasmatales being secondarily abundant; both of them are known to produce tetraether lipids and may be responsible for the enhanced archaeal lipids in the hydrate samples. MC 118 is designed to be a seafloor observatory in the Gulf of Mexico and our study represents the initial efforts in characterizing archaeal populations and their role in carbon cycle at this location. Keywords: archaeagas hydratesGDGTsGulf of Mexico16S rRNA gene Sleeper, Scott Sharpe and Derek Ross and the crew of R/V Pelican for helping with sampling, and thank Noelle Garvin and Gary Mills for technical assistance. Ann Pearson at Harvard University helped with the analysis of archaeal lipids and Yige Zhang helped with drawing of some of the figures. This research was supported by the University of Mississippi Gulf of Mexico Hydrates Research Consortium with funding from the Minerals Management Service of the Department of the Interior, the National Energy Technology Laboratory of the Department of Energy and the National Institute for Undersea Science and Technology of the National Oceanographic and Atmospheric Administration of the Department of Commerce. The China Natural Science Foundation also provided partial support (40606032) for this research (PW). Notes †The standard error of the relative abundance is ∼± 2%. ∗not detected. ∗ Determined by DOTUR with a cutoff value of 3%.