In Situ Production of Crenarchaeol in Two California Hot Springs

Crenarchaeol, a membrane-spanning glycerol dialkyl glycerol tetraether (GDGT) containing a cyclohexane moiety in addition to four cyclopentane moieties, was originally hypothesized to be synthesized exclusively by the mesophilic Crenarchaeota. Recent studies reporting the occurrence of crenarchaeol in hot springs and as a membrane constituent of the recently isolated thermophilic crenarchaeote "Candidatus Nitrosocaldus yellowstonii," however, have raised questions regarding its taxonomic distribution and function. To determine whether crenarchaeol in hot springs is indeed synthesized by members of the Archaea in situ or is of allochthonous origin, we quantified crenarchaeol present in the form of both intact polar lipids (IPLs) and core lipids in sediments of two California hot springs and in nearby soils. IPL-derived crenarchaeol (IPL-crenarchaeol) was found in both hot springs and soils, suggesting in situ production of this GDGT over a wide temperature range (12 degrees C to 89 degrees C). Quantification of archaeal amoA gene abundance by quantitative PCR showed a good correspondence with IPL-crenarchaeol, suggesting that it was indeed derived from living cells and that crenarchaeol-synthesizing members of the Archaea in our samples may also be ammonia oxidizers.