Merging isotopes and community genomics in a siliceous sinter-depositing hot spring

Abstract

[1] Thermophilic microbes in hydrothermal ecosystems have multiple metabolic strategies for taking up carbon and nitrogen, which may result in distinct stable isotopic compositions of C and N in living biomass, as well as other biosignatures that accumulate in the geologic record. Biofilms from "Bison Pool" at Yellowstone National Park display large variations in carbon and nitrogen isotopic values as a function of downstream sampling and illustrate the presence of large shifts in ecological functions as temperature decreases. This is the first study to couple isotopic data with community genomic analysis to predict dominant carbon fixation pathways that create hydrothermal biofilm signatures. The results also suggest nitrogen limitation through the chemotrophic zone and nitrogen fixation in the lower-temperature phototrophic zone.

Hot Spring Microbial Community Composition, Morphology, and Carbon Fixation: Implications for Interpreting the Ancient Rock Record

“…The only exception was Site 3, where incubation assay carbon contents were higher than the natural abundance samples, and the Dark and DCMU treatments had δ 13 C values indistinguishable from the natural abundance samples. The large range in carbon content is likely linked to the relative ages of samples collected, with organic carbon content inversely correlated to the amount of amorphous silica precipitate accumulated by the filaments (Havig, 2009;Havig et al, 2011). The similarity between natural abundance and Dark and DCMU incubation assays is linked to a lack of uptake of 13 C-labeled DIC (reported and discussed below).…”

“…Natural abundance samples were dried as described without the acid washing step used for assay biomass samples. Previous work has demonstrated that silica-saturated Yellowstone hydrothermal water sampled is undersaturated with respect to carbonate minerals, and that there was no effect from carbonate minerals on biomass carbon stable isotope values (Havig, 2009). Recent work has demonstrated intracellular precipitation of carbonate minerals by thermophilic cyanobacteria (e.g., Benzerara et al, 2014).…”

“…GOPA itself is roughly 1 km 2 and drains into Goose Lake and its outflow stream to the north. Due to the rich biodiversity and geochemical gradients, GOPA is often used as a study site for microbial phylogenetics as well as geothermal research (Barns et al, 1994;Hugenholtz et al, 1998;Meyer-Dombard et al, 2005;Shock et al, 2005;Spear et al, 2005;Havig, 2009;Berelson et al, 2011;Mata et al, 2012;Pepe-Ranney et al, 2012).…”

“…To minimize sampling impact, the stromatolite natural abundance sample were taken from Havig (2009), collected from approximately the same location in 2005 and 2006 and analyzed as described in Havig (2009). Assays were thawed and biomass was washed with HCl (1 M) to remove any extra 13 C-labeled DIC, triple washed with 18.2 M /cm deionized water, then dried (60 • C for 3 days).…”

“…In addition, mat and filament formation can proceed in the absence of cyanobacteria. For instance, filaments and microbial mats have been observed in cave systems in the absence of light (e.g., Engel et al, 2003Engel et al, , 2004Macalady et al, 2006;Northup et al, 2011), near deep-sea hydrothermal vents (e.g., Jannasch and Wirsen, 1981;Kato et al, 2009), and in geothermal springs where geochemical conditions or temperature preclude photosynthesis (e.g., Havig et al, 2011). Similar to morphological identification, carbon isotope fractionation can be ambiguous-carbon fixation pathways of photoautotrophs and chemoautotrophs can produce biomass that is indistinguishable (e.g., Havig et al, 2011Havig et al, , 2017.…”