Lipid Biomarker Record of the Serpentinite-Hosted Ecosystem of the Samail Ophiolite, Oman and Implications for the Search for Biosignatures on Mars

Abstract

Serpentinization is a weathering process in which ultramafic rocks react with water, generating a range of products, including serpentine and other minerals, in addition to H 2 and low-molecular-weight hydrocarbons that are capable of sustaining microbial life. Lipid biomarker analyses of serpentinite-hosted ecosystems hold promise as tools for investigating microbial activity in ancient Earth environments and other terrestrial planets such as Mars because lipids have the potential for longer term preservation relative to DNA, proteins, and other more labile organic molecules. Here, we report the first lipid biomarker record of microbial activity in the mantle section of the Samail Ophiolite, in the Sultanate of Oman, a site undergoing active serpentinization. We detected isoprenoidal (archaeal) and branched (bacterial) glycerol dialkyl glycerol tetraether (GDGT) lipids, including those with 0-3 cyclopentane moieties, and crenarchaeol, an isoprenoidal GDGT containing four cyclopentane and one cyclohexane moieties, as well as monoether lipids and fatty acids indicative of sulfatereducing bacteria. Comparison of our geochemical data and 16S rRNA data from the Samail Ophiolite with those from other serpentinite-hosted sites identifies the existence of a common core serpentinization microbiome. In light of these findings, we also discuss the preservation potential of serpentinite lipid biomarker assemblages on Earth and Mars. Continuing investigations of the Samail Ophiolite and other terrestrial analogues will enhance our understanding of microbial habitability and diversity in serpentinite-hosted environments on Earth and elsewhere in the Solar System.

The Sources of Organic Carbon in the Deepest Ocean: Implication From Bacterial Membrane Lipids in the Mariana Trench Zone

“…Meanwhile, relatively high levels of BrGDGTs have also been reported in studies on chemoautotrophic systems, such as seafloor cold seep (Zhang et al, 2020), hydrothermal fields (Hu et al, 2012;Lincoln et al, 2013;Pan et al, 2016), and serpentinitehosted ecosystems (Newman et al, 2020). For example, the BIT of hydrothermal sediments of the Lau Basin (Hu et al, 2012), and the low temperature hydrothermal deposits from the Southwest Indian Ridge (Pan et al, 2016) ranged in 0.1-0.76 and 0.24-0.69, respectively.…”

“…Therefore, this index is previously used to characterize the contribution of terrestrial soil inputs in marine environments (Schouten et al, 2013). However, several previous studies have found that relatively high BrGDGT content also presented in some chemoautotrophic systems, such as cold seep (Zhang et al, 2020), hydrothermal fields (Hu et al, 2012;Lincoln et al, 2013;Pan et al, 2016), and serpentinite-hosted ecosystems (Newman et al, 2020). These findings indicated that the high relative abundance of BrGDGT in the sedimentary environment of Open Ocean may be an indicator of the chemoautotrophic ecosystem.…”

Microbial biomarkers reveal a hydrothermally active landscape at Olduvai Gorge at the dawn of the Acheulean, 1.7 Ma

“…Samples collected from the LAS layer show a very unusual distribution of functionalized lipids, including monoalkyl glycerol monoethers (MAGEs), which have been often interpreted as biomarkers for sulfate-reducing bacteria (SRB) and/or thermophilic organisms (27,28,37), among other possible biological sources (38,39). These glycerol ether lipids are sometimes present in high concentrations at marine hydrothermal vents and cold seeps and in terrestrial geothermal sediments (27)(28)(29)(30). These compounds are structurally stable and might represent the diagenetic products of mixed glycerol ester/ether mixed lipids present in the aforementioned microbial communities.…”

Accessing the Subsurface Biosphere Within Rocks Undergoing Active Low‐Temperature Serpentinization in the Samail Ophiolite (Oman Drilling Project)

“…In addition, there is significant secondary mineralization, dominated by sulfide or Fe(III)‐bearing phases, that can play a critical role in preserving cellular structures that can serve as organic biosignatures and microbial fossils (Parenteau et al., 2014). Cells mineralized in veins could be excellent repositories for microbial membrane lipids (e.g., Klein et al., 2015; Newman et al., 2020; Zwicker et al., 2018). Moreover, since this is still an active system, it provides an excellent opportunity to design studies that can distinguish between lipid biomarkers associated with the active versus fossil microbial communities, by analysis of intact polar lipids versus core lipids (e.g., Li et al., 2020 vs. Newman et al., 2020), to correlate the signature of active microbial communities to distinct geochemical regimes, and to examine the relative preservation potential of different membrane lipids.…”