Lipid Hydrogen Stable Isotope Probing Reveals Decadal-Scale Generation Times for Archaea in Hot Spring Sediments
Quantifying the lipid biosynthesis rate of archaea in hot spring sediments is necessary to estimate their generation times and environmental significance, with implications for modern biogeochemical cycling and astrobiology. Here, we performed lipid hydrogen stable isotope probing (LH-SIP) experiments on sediments collected from two high-temperature, suboxic, circumneutral hot springs in Yellowstone National Park (USA) and El Tatio Geyserfield (Chile). We determined the incorporation rate of 2H2O into intact polar lipids (IPLs) during short-duration, ex situ incubations, which provides a taxon- and metabolism-agnostic quantification of biosynthesis under near-natural conditions. We targeted isoprenoid glycerol dialkyl glycerol tetraether lipids (iGDGTs) and recovered structures with 0 to 7 cyclopentyl moieties from both springs. We observed minor 2H-uptake into archaeal IPL-iGDGT-derived biphytanes in spring sediments in Yellowstone, corresponding to decadal-scale apparent generation times (16 +/- 3 years), and no detectable uptake in El Tatio sediments, where lipid turnover was slower than could be resolved under the experimental conditions (maximum resolvable apparent generation times ~ 42 +/- 21 years). We conclude that these slow apparent generation times likely reflect substantial dilution by a large standing IPL pool and/or recycling or re-functionalization of relict lipid components, rather than equivalently slow rates of archaeal cell division. These are the first estimates of archaeal lipid production rates in terrestrial hydrothermal systems using LH-SIP incubations and provide critical constraints for interpreting archaeal lipids in modern systems and ancient hot spring deposits.