Biogeochemical evidence that thermophilic archaea mediate the anaerobic oxidation of methane

Abstract

Distributions and isotopic analyses of lipids from sediment cores at a hydrothermally active site in the Guaymas Basin with a steep sedimentary temperature gradient revealed the presence of archaea that oxidize methane anaerobically. The presence of strongly (13)C-depleted lipids at greater depths in the sediments suggests that microbes involved in anaerobic oxidation of methane are present and presumably active at environmental temperatures of >30 degrees C, indicating that this process can occur not only at cold seeps but also at hydrothermal sites. The distribution of the membrane tetraether lipids of the methanotrophic archaea shows that these organisms have adapted their membrane composition to these high environmental temperatures.

FIG. 1.

Structures of GDGTs as discussed in the text.

FIG. 2.

Base peak chromatograms of HPLC-MS analysis of GDGTs in core 2 at the three depth intervals examined. Peak numbers refer to GDGT numbers of the structures in Fig. 1. cr., crenarchaeol.

FIG. 3.

Concentrations of biomarker lipids as a function of depth in core 2 from the Guaymas Basin. Note the logarithmic scale.

FIG. 4.

Concentrations (a) and relative distributions (b) of GDGTs in core 2 from the Guaymas Basin as a function of depth.

FIG. 5.

Bar diagrams of the relative distribution of GDGTs in a Black Sea water column sample (28) (a), a Mediterranean cold seep site (16) (b), core 2 (5 to 10 cm) from the Guaymas Basin (c), and GDGTs of S. solfaticarus (d) (11). GDGT numbers refer to GDGT numbers of the structures in Fig. 1. av. cycl., weighted average of the number of cyclopentane rings.