Lack of 13C-label incorporation suggests low turnover rates of thaumarchaealintact polar tetraether lipids in sediments from the Iceland shelf

[摘要] Thaumarchaeota are amongst the most abundant microorganisms in aquaticenvironments, however, their metabolism in marine sediments is stilldebated. Labeling studies in marine sediments have previously beenundertaken, but focused on complex organic carbon substrates whichThaumarchaeota have not yet been shown to take up. In this study, weinvestigated the activity of Thaumarchaeota in sediments by supplyingdifferent ¹³C-labeled substrates which have previously been shown to beincorporated into archaeal cells in water incubations and/or enrichmentcultures. We determined the incorporation of ¹³C-label frombicarbonate, pyruvate, glucose and amino acids into thaumarchaeal intactpolar lipid-glycerol dibiphytanyl glycerol tetraethers (IPL-GDGTs) during4–6 day incubations of marine sediment cores from three sites on the Icelandshelf. Thaumarchaeal intact polar lipids, in particular crenarchaeol, weredetected at all stations and concentrations remained constant or decreasedslightly upon incubation. No ¹³C incorporation in any IPL-GDGT wasobserved 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‰ ) wasfound. ¹³C was also respired during the experiment as shown by asubstantial increase in the ¹³C content of the dissolved inorganiccarbon. In IPL-GDGTs recovered from the sandy sediments at station 1,however, some enrichment in δ¹³C (1–4‰ )was detected after incubation with bicarbonate and pyruvate. The lowincorporation rates suggest a low activity of Thaumarchaeota in marinesediments and/or a low turnover rate of thaumarchaeal IPL-GDGTs due to theirlow degradation rates. Cell numbers and activity of sedimentaryThaumarchaeota based on IPL-GDGT measurements may thus have previously beenoverestimated.

[学科分类] 地球化学与岩石