Lack of <sup>13</sup>C-label incorporation suggests low turnover rates of thaumarchaeal intact polar tetraether lipids in sediments from the Iceland Shelf

Abstract

Thaumarchaeota are amongst the most abundant microorganisms in aquatic environments, however, their metabolism in marine sediments is still debated. Labeling studies in marine sediments have previously been undertaken, but focused on complex organic carbon substrates which Thaumarchaeota have not yet been shown to take up. In this study, we investigated the activity of Thaumarchaeota in sediments by supplying different ¹³C-labeled substrates which have previously been shown to be incorporated into archaeal cells in water incubations and/or enrichment cultures. We determined the incorporation of ¹³C-label from bicarbonate, pyruvate, glucose and amino acids into thaumarchaeal intact polar lipid-glycerol dibiphytanyl glycerol tetraethers (IPL-GDGTs) during 4–6 day incubations of marine sediment cores from three different sites on the Iceland Shelf. Thaumarchaeal intact polar lipids were detected at all stations and concentrations remained constant or decreased slightly upon incubation. No ¹³C incorporation in any IPL-GDGT was observed at stations 2 (clay-rich sediment) and 3 (organic-rich sediment). In bacterial/eukaryotic IPL-derived fatty acids at station 3, contrastingly, a large uptake of ¹³C label (up to +80‰) was found. ¹³C was also respired during the experiment as shown by a substantial increase in the ¹³C content of the dissolved inorganic carbon. In IPL-GDGTs recovered from the sandy sediments at station 1, however, some enrichment in ¹³C (1–4‰) was detected after incubation with bicarbonate and pyruvate. The low incorporation rates suggest a low activity of Thaumarchaeota in marine sediments and/or a low turnover rate of thaumarchaeal IPL-GDGTs due to their low degradation rates. Cell numbers and activity of sedimentary Thaumarchaeota based on IPL-GDGT measurements may thus have previously been overestimated

Novel archaeal tetraether lipids with a cyclohexyl ring identified in Fayetteville Green Lake, NY, and other sulfidic lacustrine settings

“…Because the δ 13 C value of biph.‐S is more than 16 ‰ lower than that of TOC, it is unlikely to represent a heterotrophic signal. Instead, the carbon isotope depletion of around 20 ‰ in archaeal lipids compared to DIC (Δδ 13 C, −20 ‰) has been observed in chemoautotrophic Thaumarchaeota with both laboratory incubation and environmental studies . We propose that the −44.6 ‰ δ 13 C value for biph.‐S may originate from chemoautotrophic archaea that assimilate DIC in FGL.…”

Sources, Ages, and Alteration of Organic Matter in Estuaries

“…Additional advances have allowed investigators to trace 13 C incorporation into archaeal biomarkers, providing opportunities to assess the role of archaea in OM decomposition. Lengger et al (2014) conducted a decomposition study using 13 C-labeled C org and were unable to detect significant 13 C-label incorporation in Thaumarchaea-derived intact polar lipids (GDGTs), whereas bacteria assimilated and respired the added C org , indicating that these archaea were not important in processing labile C org in Iceland shelf sediments.…”

A robust nitrifying community in a bioreactor at 50 °C opens up the path for thermophilic nitrogen removal

“…The remaining polar fractions were subjected to chemical treatment to release the biphytanyl chains from the tetraether lipids (Lengger et al, 2014). The stable carbon isotopic composition of the released biphytanes was analyzed in replicate using an Agilent 6800 GC coupled to a Thermo Fisher Delta V isotope ratio monitoring mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) (Lengger et al, 2014).…”