Intact polar lipidome and membrane adaptations of microbial communities inhabiting serpentinite-hosted fluids

The generation of hydrogen and reduced carbon compounds during serpentinization provides sustained energy for microorganisms on Earth, and possibly on other extraterrestrial bodies (e.g., Mars, icy satellites). However, the geochemical conditions that arise from water-rock reaction also challenge the known limits of microbial physiology, such as hyperalkaline pH, limited electron acceptors and inorganic carbon. Because cell membranes act as a primary barrier between a cell and its environment, lipids are a vital component in microbial acclimation to challenging physicochemical conditions. To probe the diversity of cell membrane lipids produced in serpentinizing settings and identify membrane adaptations to this environment, we conducted the first comprehensive intact polar lipid (IPL) biomarker survey of microbial communities inhabiting the subsurface at a terrestrial site of serpentinization. We used an expansive, custom environmental lipid database that expands the application of targeted and untargeted lipodomics in the study of microbial and biogeochemical processes. IPLs extracted from serpentinite-hosted fluid communities were comprised of >90% isoprenoidal and non-isoprenoidal diether glycolipids likely produced by archaeal methanogens and sulfate-reducing bacteria. Phospholipids only constituted ~1% of the intact polar lipidome. In addition to abundant diether glycolipids, betaine and trimethylated-ornithine aminolipids and glycosphingolipids were also detected, indicating pervasive membrane modifications in response to phosphate limitation. The carbon oxidation state of IPL backbones was positively correlated with the reduction potential of fluids, which may signify an energy conservation strategy for lipid synthesis. Together, these data suggest microorganisms inhabiting serpentinites possess a unique combination of membrane adaptations that allow for their survival in polyextreme environments. The persistence of IPLs in fluids beyond the presence of their source organisms, as indicated by 16S rRNA genes and transcripts, is promising for the detection of extinct life in serpentinizing settings through lipid biomarker signatures. These data contribute new insights into the complexity of lipid structures generated in actively serpentinizing environments and provide valuable context to aid in the reconstruction of past microbial activity from fossil lipid records of terrestrial serpentinites and the search for biosignatures elsewhere in our solar system

An improved regional branched GDGT-based soil temperature calibration for 1 the Tropical Andes of Colombia: Towards a soil calibration for the tropics.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial cell membrane lipids that, when preserved in sedimentary archives, can be used to infer continental paleotemperatures. Although commonly used global calibrations capture a relationship between the distribution of brGDGTs and temperature, they underestimate temperatures for tropical regions as much as ~16&deg;C. Furthermore, some global calibrations reach saturation at around 24&ndash;25&deg;C, and, in general, they have root-mean-squared errors (RMSEs&nbsp;&asymp;&nbsp;~4&deg;C) that are too large for them to resolve small variations in paleoclimate variability in tropical regions. We present an in situ regional calibration of soil brGDGTs along altitudinal transects on both flanks of the Eastern Cordillera of Colombia in the northern tropical Andes that spans ~3,200&nbsp;m in elevation and 17&deg;C and 19&deg;C in mean annual soil and air temperatures, respectively. These new soil and air regional calibrations yield RMSEs of 1.5&deg;C and 1.9&deg;C, respectively. When combined with existing data from elsewhere in the tropics, the integrated data (n&nbsp;=&nbsp;175) not only fit a linear calibration with a RMSE of 2.7&deg;C but also fit a nonlinear calibration with a RMSE of 2.2&deg;C. These calibrations allow for a more precise and reliable reconstruction of past temperatures in the tropics than global calibrations. </div

Bacterial and archaeal lipids trace chemo(auto)trophy along the redoxcline in Vancouver Island fjords

Abstract Marine oxygen minimum zones play a crucial role in the global oceanic carbon, nitrogen, and sulfur cycles as they harbor microbial communities that are adapted to the water column chemistry and redox zonation, and in turn control the water column chemistry and greenhouse gas release. These micro‐organisms have metabolisms that rely on terminal electron acceptors other than O2 and often benefit from syntrophic relationships (metabolic coupling). Here, we study chemo(auto)trophy along the redoxcline in two stratified fjords on Vancouver Island (Canada) using bacterial bacteriohopanepolyols and archaeal ether lipids. We analyze the distribution of these lipid classes in suspended particulate matter (SPM) to trace ammonia oxidation, anaerobic ammonium oxidation (anammox), sulfate reduction/sulfur oxidation, methanogenesis, and methane oxidation, and investigate ecological niches to evaluate potential links between their respective bacterial and archaeal sources. Our results show an unparalleled BHP and ether lipid structural diversity that allows tracing the major redox‐driven metabolic processes at the time of sampling: Both fjords are dominated by archaeal ammonia oxidation and anammox; sulfate‐reducing bacteria may be present in Deer Bay, but absent from Effingham Inlet; methanogenic Euryarchaeota and archaeal and bacterial methanotrophs are detectable at low abundance. Correlation analysis reveals distinct biomarker clusters that provide constraints on the biogeochemical niches of some orphan BHP and ether lipids such as in situ‐produced adenosyl‐BHPs or unsaturated archaeols.Universität zu Köln http://dx.doi.org/10.13039/501100008001University of Colorado Boulder http://dx.doi.org/10.13039/100007493INSTAARUS National Science Foundation Chemical Oceanography Program http://dx.doi.org/10.13039/100000001Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Compound-specific carbon isotope results from the SH#1 core analyzed and processed at University of Colorado Boulder

This data set was used to trace changes in carbon cycling and productivity in the Western Interior Seaway (WIS) through Oceanic Anoxic Event 2 (OAE2; 94 Ma). Samples were present in the SH#1 core, which was recovered in the summer of 2014 near Big Water, Utah (37.158466°N, 111.531947°W). Compound-specific carbon isotope data was produced using gas chromatography-isotope ratio mass spectrometry (GCIRMS) between February 2017 and November 2018. Raw data were used in calculations described in Boudinot et al., (in review) to estimate changes in the carbon isotopic composition of marine DIC and atmospheric CO2, as well as changes in pCO2, throughout OAE2, all of which are outlined in the data file. Assumptions and estimates of environmental conditions impacting these estimated carbon-cycle relevant metrics are presented. These data demonstrate both the methods and outputs of using compound-specific carbon isotope analyses to estimate local and global carbon cycle dynamics during an interval of global change during Earth history. Specifically, the data file includes (A) core depth in meters of the SH#1 core, (B) the name of the compound identified using GC-MS (in Boudinot et al., 2020, Neritic ecosystem response to Oceanic Anoxic Event 2 in the Cretaceous Western Interior Seaway, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 546, 109673), (C) the calibrated mean carbon isotopic composition of the compound in per mil relative to VPDB, (D) the preparation undertaken prior to analysis on GC-IRMS (i.e., either having undergone urea adduction or not), (E) the carbon isotopic composition of carbonate from the same depth as presented in Jones et al. (2019, Astronomical pacing of relative sea level during Oceanic Anoxic Event 2: Preliminary studies of the expanded SH#1 core, Utah, USA. GSA Bulletin, 131 (9-10): 1702–1722) or as analyzed in Boudinot et al. (in review) (described in methods, indicated in figures), (F) the analytical standard deviation of the carbon isotopic composition of compounds based on either duplicate analysis, or on the predicted standard error based on the calibration ("true_d13c_pred_se" in isoprocessor), (G) the number of duplicate compound-specific analyses, with NA indicating that only one analysis was performed and thus the predicted standard error based on the calibration was used to estimate the standard deviation, (H-I) the minimum and maximum net carbon isotope fractionation during carbon fixation and biosynthesis for the autotroph responsible for each lipid synthesis, in per mil, (J-L) the minimum, maximum, and average fixed inorganic carbon pool carbon isotopic composition estimated using the equations presented in Boudinot et al. (in review), (M) temperature estimate in degrees kelvin, (N) the calculated temperature-dependent carbon isotope fractionation of CO2 with respect to bicarbonate in per mil, (O) the carbon isotopic composition of marine DIC based on the carbon isotopic composition of carbonate for that depth in per mil, (P-R) the minimum, maximum, and average carbon isotopic composition of primary photosynthate calculated using the equation described in Boudinot et al. (in review) in per mil, (S) the carbon isotopic fractionation associated with photosynthesis in per mil, (T) the solubility constant of CO2 based on salinity and temperature estimates relevant to the SH#1 core, (U-V) the high and low b-value estimates used as constants to represent the role of productivity in modulating carbon isotope fractionation during photosynthesis, (W) the carbon isotopic composition of aqueous CO2 estimated using the carbon isotopic composition of carbonate, (X) the carbon isotopic composition of aqueous CO2 estimated using the carbon isotopic composition of biomarkers, (Y) epsilon p estimated using b values, the calculated carbon isotopic composition of primary photosynthate, and the calculated carbon isotopic composition of aqueous CO2 estimated using carbonate, (Z-AA) the high and low estimates of the aqueous concentration of CO2 in seawater at the SH#1 core location using epsilon p estimates from the carbon isotopic composition of carbonate, in micromol CO2/kg, (AB-AC) the high and low estimates of pCO2 using the estimate of aqueous CO2 derived from the carbon isotopic composition of carbonate, in ppmv, (AD) epsilon p estimated using b values, the calculated carbon isotopic composition of primary photosynthate, and the calculated carbon isotopic composition of aqueous CO2 estimated using biomarkers, (AE-AF) the high and low estimates of the aqueous concentration of CO2 in seawater at the SH#1 core location using epsilon p estimates from the carbon isotopic composition of biomarkers, in micromol CO2/kg, and (AG-AH) the high and low estimates of pCO2 using the estimate of aqueous CO2 derived from the carbon isotopic composition of biomarkers, in ppmv