Factors controlling the distribution of archaeal tetraethers in terrestrial hot springs

Abstract

Glycerol dialkyl glycerol tetraethers (GDGTs) found in hot springs reflect the abundance and community structure of Archaea in these extreme environments. The relationships between GDGTs, archaeal communities, and physical or geochemical variables are underexamined to date and when reported often result in conflicting interpretations. Here, we examined profiles of GDGTs from pure cultures of Crenarchaeota and from terrestrial geothermal springs representing a wide distribution of locations, including Yellowstone National Park (United States), the Great Basin of Nevada and California (United States), Kamchatka (Russia), Tengchong thermal field (China), and Thailand. These samples had temperatures of 36.5 to 87 degrees C and pH values of 3.0 to 9.2. GDGT abundances also were determined for three soil samples adjacent to some of the hot springs. Principal component analysis identified four factors that accounted for most of the variance among nine individual GDGTs, temperature, and pH. Significant correlations were observed between pH and the GDGTs crenarchaeol and GDGT-4 (four cyclopentane rings, m/z 1,294); pH correlated positively with crenarchaeol and inversely with GDGT-4. Weaker correlations were observed between temperature and the four factors. Three of the four GDGTs used in the marine TEX(86) paleotemperature index (GDGT-1 to -3, but not crenarchaeol isomer) were associated with a single factor. No correlation was observed for GDGT-0 (acyclic caldarchaeol): it is effectively its own variable. The biosynthetic mechanisms and exact archaeal community structures leading to these relationships remain unknown. However, the data in general show promise for the continued development of GDGT lipid-based physiochemical proxies for archaeal evolution and for paleo-ecology or paleoclimate studies.

FIG. 1.

Representative chromatograms for GDGTs from selected hot springs, with temperature and pH values. (a to d) Samples at high temperatures (>80°C): (a) Surprise Valley white streamers (55); (b) Surprise Valley mat community (beneath white streamers) (61); (c) Cistern Spring, Yellowstone; (d) Perpetual Spouter-B, Yellowstone. (e to h) Samples near 65°C: (e) Beowulf ED-1, Yellowstone; (f) Whirligig Geyser, Yellowstone; (g) Rubber Mat, Kamchatka; (h) Vent 1 North, Kamchatka. (i to l) Samples rich in crenarchaeol: (i) Buffalo Valley-2, Nevada (61); (j) Rick's Hot Creek (61); (k) Paradise Valley (36); (l) Seven Devils (61). (m) Pure culture of Acidilobus saccharovorans 345-15.

FIG. 2.

Histograms comparing relative abundances of GDGTs from three crenarchaeol-rich hot springs and their surrounding soils. (a) Rick's Hot Creek. (b) Eagleville. (c) Surprise Valley. Cr, crenarcheaeol; iso, crenarchaeol isomer.

FIG. 3.

GDGT cluster tree with sample labels. Labels for sample locations are color coded: Nevada, green; Yellowstone, black; Kamchatka, dark blue; Tengchong, red; Thailand, pink; and pure cultures, light blue. Histograms of GDGTs are colored from left (GDGT-0, red) to right (GDGT-6′, turquoise), in the order of the GDGT columns in Table 1 and the marker symbols in Fig. 1. Group designations are as discussed in the text.

FIG. 4.

Temperature and pH data for samples in the order in which they appear in the cluster diagram (Fig. 3). Sample 1 represents Buffalo Valley-1, while sample 51 represents Acidilobus aceticus 1904.

FIG. 5.

Results from PCA. Samples are colored to match the geographic color codes used in Fig. 3. (a) The relationship between environmental factors A, B, and D shows that the samples form a “tent” or V shape around an apex between factors A and D. (b) Factor D relative to factor A shows the grouping of Yellowstone and Kamchatka samples with pure cultures and Great Basin (Nevada and California) samples with the single Thailand sample. (c and d) There is no pattern in the relationship between factor A or D and factor B, but samples from common geographic origins tend to cluster together.