Nonmarine crenarchaeol in Nevada hot springs

Abstract

Glycerol dialkyl glycerol tetraethers (GDGTs) are core membrane lipids of the Crenarchaeota. The structurally unusual GDGT crenarchaeol has been proposed as a taxonomically specific biomarker for the marine planktonic group I archaea. It is found ubiquitously in the marine water column and in sediments. In this work, samples of microbial community biomass were obtained from several alkaline and neutral-pH hot springs in Nevada, United States. Lipid extracts of these samples were analyzed by high-performance liquid chromatography-mass spectrometry and by gas chromatography-mass spectrometry. Each sample contained GDGTs, and among these compounds was crenarchaeol. The distribution of archaeal lipids in Nevada hot springs did not appear to correlate with temperature, as has been observed in the marine environment. Instead, a significant correlation with the concentration of bicarbonate was observed. Archaeal DNA was analyzed by denaturing gradient gel electrophoresis. All samples contained 16S rRNA gene sequences which were more strongly related to thermophilic crenarchaeota than to Cenarchaeum symbiosum, a marine nonthermophilic crenarchaeon. The occurrence of crenarchaeol in environments containing sequences affiliated with thermophilic crenarchaeota suggests a wide phenotypic distribution of this compound. The results also indicate that crenarchaeol can no longer be considered an exclusive biomarker for marine species.

FIG. 1.

Map of hot spring locations in Nevada and California.

FIG. 2.

HPLC-MS chromatograms of intact GDGTs from Santa Monica Basin surface sediment (a), Crescent Valley (b), and Eagleville (c). GDGTs are enumerated I to VI as in reference . Peak II is acyclic GDGT, while peak I is crenarchaeol.

FIG. 3.

Coinjection of C₄₀ isoprenoid hydrocarbons from Santa Monica Basin (SMB) and from Paradise Valley.

FIG. 4.

Coinjections of C_40:3 isoprenoid hydrocarbons: pure Santa Monica Basin surface sediment (a), Eagleville (25%) plus Santa Monica Basin (75%) (b), and Paradise Valley (47%) plus Santa Monica Basin (53%) (c). Solid lines represent raw data; calculated Gaussian curves are shown as dashed lines. Residuals for each model are shown in panels d, e, and f. One-sigma peak widths are in minutes.

FIG. 5.

Ratios of the peak areas of GDGTs in Nevada hot springs and Santa Monica Basin as a function of HCO₃⁻ concentration and water temperature. Ring index is given versus log[HCO₃⁻] (a) and versus temperature (b). TEX₈₆ is given versus log[HCO₃⁻] (c) and versus temperature (d).

FIG. 6.

Denaturing gradient gel electrophoresis gel (a) and neighbor-joining tree (b) for environmental sequences from Nevada hot springs. PV, Paradise Valley; EV, Eagleville Valley; CV, Crescent Valley. The scale bar in panel b indicates 10 substitutions per 100 nucleotide positions.