Abstract
Branched glycerol dialkyl glycerol tetraethers (bGDGTs) are predominantly found in soils and peat bogs. In this study, we analyzed core (C)-bGDGTs after hydrolysis of polar fractions using liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry and analyzed intact P-bGDGTs using total lipid extract (TLE) without hydrolysis by liquid chromatography-electrospray ionization-multiple stage mass spectrometry. Our results show multiple lines of evidence for the production of bGDGTs in sediments and cellulolytic enrichments in a hot spring (62–86°C) in the Great Basin (USA). First, in situ cellulolytic enrichment led to an increase in the relative abundance of hydrolysis-derived P-bGDGTs over their C-bGDGT counterparts. Second, the hydrolysis-derived P- and C-bGDGT profiles in the hot spring were different from those of the surrounding soil samples; in particular, a monoglycosidic bGDGT Ib containing 13,16-dimethyloctacosane and one cyclopentane moiety was detected in the TLE but it was undetectable in surrounding soil samples even after sample enrichments. Third, previously published 16S rRNA gene pyrotag analysis from the same lignocellulose samples demonstrated the enrichment of thermophiles, rather than mesophiles, and total bGDGT abundance in cellulolytic enrichments correlated with the relative abundance of 16S rRNA gene pyrotags from thermophilic bacteria in the phyla Bacteroidetes, Dictyoglomi, EM3, and OP9 (“Atribacteria”). These observations conclusively demonstrate the production of bGDGTs in this hot spring; however, the identity of organisms that produce bGDGTs in the geothermal environment remains unclear.
Highlights
Recent advances in liquid chromatography-mass spectrometry (LC-MS) have significantly expanded our view of the occurrence of unique lipid biomarkers in the natural environment (Hopmans et al, 2000; Schouten et al, 2000, 2013; Sturt et al, 2004; Liu et al, 2012)
Branched glycerol dialkyl glycerol tetraethers are unusual lipids that have been detected in a variety of natural settings using LC-MS, including soil and peat bogs (Hopmans et al, 2004; Weijers et al, 2006, 2007a; Peterse et al, 2009, 2010, 2012; Liu et al, 2010), lakes (Sinninghe Damsté et al, 2009; Tierney and Russell, 2009; Tierney et al, 2011; Sun et al, 2011; Wang et al, 2012), rivers and estuaries (Kim et al, 2010, 2012; Zhu et al, 2011; Zhang et al, 2012; Yang et al, 2013), and continental margin sediments (Weijers et al, 2007b,c; Schouten et al, 2008; Rueda et al, 2009; Bendle et al, 2010)
ABUNDANCE OF C- AND HYDROLYSIS-DERIVED P-Branched glycerol dialkyl glycerol tetraethers (bGDGTs) Sediment samples from the hot spring had C-bGDGTs ranging from 12 ng/g dry sediment to 280 ng/g dry sediment (Table 1), www.frontiersin.org bGDGTs from Nevada hot spring bGDGTs
Summary
Recent advances in liquid chromatography-mass spectrometry (LC-MS) have significantly expanded our view of the occurrence of unique lipid biomarkers in the natural environment (Hopmans et al, 2000; Schouten et al, 2000, 2013; Sturt et al, 2004; Liu et al, 2012). The sample code for cellulolytic enrichments consists of three parameters, temperature (77◦C or 85◦C), cellulose substrate (A, aspen shavings; C, corn stover), and incubation environment (W, suspended in water; S, buried in sediment) as described earlier (Peacock et al, 2013).
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