Serum Lipidomic Screen Identifies Key Metabolites, Pathways, and Disease Classifiers in Crohn's Disease

BACKGROUND

There is an unmet medical need for biomarkers that capture host and environmental contributions in inflammatory bowel diseases (IBDs). This study aimed at testing the potential of circulating lipids as disease classifiers given their major roles in inflammation.

METHODS

We applied a previously validated comprehensive high-resolution liquid chromatography-mass spectrometry-based untargeted lipidomic workflow covering 25 lipid subclasses to serum samples from 100 Crohn's disease (CD) patients and 100 matched control subjects. Findings were replicated and expanded in another 200 CD patients and 200 control subjects. Key metabolites were tested for associations with disease behavior and location, and classification models were built and validated. Their association with disease activity was tested using an independent cohort of 42 CD patients.

RESULTS

We identified >70 metabolites with strong association (P < 1 × 10-4, q < 5 × 10-4) to CD. Highly performing classification models (area under the curve > 0.84-0.97) could be built with as few as 5 to 9 different metabolites, representing 6 major correlated lipid clusters. These classifiers included a phosphatidylethanolamine ether (O-16:0/20:4), a sphingomyelin (d18:1/21:0) and a cholesterol ester (14:1), a very long-chain dicarboxylic acid [28:1(OH)] and sitosterol sulfate. These classifiers and correlated lipids indicate a dysregulated metabolism in host cells, notably in peroxisomes, as well as dysbiosis, oxidative stress, compromised inflammation resolution, or intestinal membrane integrity. A subset of these were associated with disease behavior or location.

CONCLUSIONS

Untargeted lipidomic analyses uncovered perturbations in the circulating human CD lipidome, likely resulting from multiple pathogenic mechanisms. Models using as few as 5 biomarkers had strong disease classifier characteristics, supporting their potential use in diagnosis or prognosis.

Consumption of Eggs Alone or Enriched with Annatto (Bixa orellana L.) Does Not Increase Cardiovascular Risk in Healthy Adults-A Randomized Clinical Trial, the Eggant Study

Most atherosclerotic cardiovascular diseases can be prevented by modifying lifestyles, including unhealthy diets. Eggs contain important carotenoids that may impact cardiovascular risk. The lipid nature of eggs can improve the bioavailability of other carotenoids, such as Annatto (Bixa orellana L.), with reported antioxidant properties. Although numerous studies have shown that there is no association between egg consumption and cardiovascular risk, there is still controversy. In addition, there is limited information about Annatto's effects on human health. This study evaluated the association between egg consumption and its enrichment with Annatto in lipid biomarkers of cardiovascular disease. In a parallel clinical trial, one hundred and five (n = 105) men and women were randomized by age, sex, and body mass index (BMI), and distributed into three groups. Subjects consumed daily, for 8 weeks, either two eggs, two eggs with Annatto, or two egg whites. Plasma lipids were measured by enzymatic colorimetric methods, plasma apolipoproteins and lipoprotein subfractions and size by nuclear magnetic resonance. There were no differences between groups in age, sex, and BMI. No significant changes were found over time or between groups in plasma triglycerides, LDL cholesterol, HDL cholesterol, apolipoprotein (apo) A1, apo B, or lipoprotein subfraction concentrations. In healthy adults, the intake of two eggs a day, or two eggs with Annatto for eight weeks, did not generate adverse changes in cardiovascular risk markers.

Intensified microbial sulfate reduction in the deep Dead Sea during the early Holocene Mediterranean sapropel 1 deposition

The hypersaline Dead Sea and its sediments are natural laboratories for studying extremophile microorganism habitat response to environmental change. In modern times, increased freshwater runoff to the lake surface waters resulted in stratification and dilution of the upper water column followed by microbial blooms. However, whether these events facilitated a microbial response in the deep lake and sediments is obscure. Here we investigate archived evidence of microbial processes and changing regional hydroclimate conditions by reconstructing deep Dead Sea chemical compositions from pore fluid major ion concentration and stable S, O, and C isotopes, together with lipid biomarkers preserved in the hypersaline deep Dead Sea ICDP-drilled core sediments dating to the early Holocene (ca. 10,000 years BP). Following a significant negative lake water balance resulting in salt layer deposits at the start of the Holocene, there was a general period of positive net water balance at 9500-8300 years BP. The pore fluid isotopic composition of sulfate exhibit evidence of intensified microbial sulfate reduction, where both δ34S and δ18O of sulfate show a sharp increase from estimated base values of 15.0‰ and 13.9‰ to 40.2‰ and 20.4‰, respectively, and a δ34S vs. δ18O slope of 0.26. The presence of the n-C₁₇ alkane biomarker in the sediments suggests an increase of cyanobacteria or phytoplankton contribution to the bulk organic matter that reached the deepest parts of the Dead Sea. Although hydrologically disconnected, both the Mediterranean Sea and the Dead Sea microbial ecosystems responded to increased freshwater runoff during the early Holocene, with the former depositing the organic-rich sapropel 1 layer due to anoxic water column conditions. In the Dead Sea prolonged positive net water balance facilitated primary production and algal blooms in the upper waters and intensified microbial sulfate reduction in the hypolimnion and/or at the sediment-brine interface.

Activity of Ancillary Heterotrophic Community Members in Anaerobic Methane-Oxidizing Cultures

Consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria mediate the anaerobic oxidation of methane (AOM) in marine sediments. However, even sediment-free cultures contain a substantial number of additional microorganisms not directly related to AOM. To track the heterotrophic activity of these community members and their possible relationship with AOM, we amended meso- (37°C) and thermophilic (50°C) AOM cultures (dominated by ANME-1 archaea and their partner bacteria of the Seep-SRB2 clade or Candidatus Desulfofervidus auxilii) with L-leucine-3-¹³C (¹³C-leu). Various microbial lipids incorporated the labeled carbon from this amino acid, independent of the presence of methane as an energy source, specifically bacterial fatty acids, such as iso and anteiso-branched C_15:0 and C_17:0, as well as unsaturated C_18:1ω9 and C_18:1ω7. In natural methane-rich environments, these bacterial fatty acids are strongly ¹³C-depleted. We, therefore, suggest that those fatty acids are produced by ancillary bacteria that grow on ¹³C-depleted necromass or cell exudates/lysates of the AOM core communities. Candidates that likely benefit from AOM biomass are heterotrophic bacterial members of the Spirochetes and Anaerolineae—known to produce abundant branched fatty acids and present in all the AOM enrichment cultures. For archaeal lipids, we observed minor ¹³C-incorporation, but still suggesting some ¹³C-leu anabolism. Based on their relatively high abundance in the culture, the most probable archaeal candidates are Bathyarchaeota, Thermoplasmatales, and Lokiarchaeota. The identified heterotrophic bacterial and archaeal ancillary members are likely key players in organic carbon recycling in anoxic marine sediments.

Advanced Lipidomics in the Modern Meat Industry: Quality Traceability, Processing Requirement, and Health Concerns

Over the latest decade, lipidomics has been extensively developed to give robust strength to the qualitative and quantitative information of lipid molecules derived from physiological animal tissues and edible muscle foods. The main lipidomics analytical platforms include mass spectrometry (MS) and nuclear magnetic resonance (NMR), where MS-based approaches [e.g., “shotgun lipidomics,” ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF-MS)] have been widely used due to their good sensitivity, high availability, and accuracy in identification/quantification of basal lipid profiles in complex biological point of view. However, each method has limitations for lipid-species [e.g., fatty acids, triglycerides (TGs), and phospholipids (PLs)] analysis, and necessitating the extension of effective chemometric-resolved modeling and novel bioinformatic strategies toward molecular insights into alterations in the metabolic pathway. This review summarized the latest research advances regarding the application of advanced lipidomics in muscle origin and meat processing. We concisely highlighted and presented how the biosynthesis and decomposition of muscle-derived lipid molecules can be tailored by intrinsic characteristics during meat production (i.e., muscle type, breed, feeding, and freshness). Meanwhile, the consequences of some crucial hurdle techniques from both thermal/non-thermal perspectives were also discussed, as well as the role of salting/fermentation behaviors in postmortem lipid biotransformation. Finally, we proposed the inter-relationship between potential/putative lipid biomarkers in representative physiological muscles and processed meats, their metabolism accessibility, general nutritional uptake, and potency on human health.

Ecological variability based on lipid biomarkers in astrobiologically interesting wetlands from the Argentinian central Andes

Andean wetlands hold extremophilic communities adapted to live in harsh conditions. Here, we investigated the microbial ecology of three high-altitude hypersaline ponds from La Puna region (Argentina) showing an increasing extent of desiccation by analyzing their lipid sedimentary record. We recreated the microbial community structure and the carbon metabolisms in each lacustrine system based on the molecular distribution of lipid biomarkers and their compound-specific carbon and hydrogen isotopic signatures. We detected lipid compounds considered to be biomarkers of cyanobacteria, sulfate-reducing bacteria, purple sulfur bacteria, and archaea in the three Andean ponds, as well as diatoms in the intermediate salinity system. The relative abundance of purple sulfur and sulfate-reducing bacteria decreased with salinity, whereas cyanobacteria and archaea decreased their relative abundance in the mid-saline pond to increase it again and became both prevailing at the highest salinity. Carbon fixation in the three ponds was driven by a combination of the reductive tricarboxylic acid cycle, the reductive pentose phosphate cycle, and the reductive acetyl-CoA pathway. This work is the first to describe molecular and isotopic lipid fingerprints in wetlands from the central Andean Puna, and serves as a basis for further biogeochemical studies in the area.

Multiple Groups of Methanotrophic Bacteria Mediate Methane Oxidation in Anoxic Lake Sediments

Freshwater lakes represent an important source of the potent greenhouse gas methane (CH4) to the atmosphere. Methane emissions are regulated to large parts by aerobic (MOx) and anaerobic (AOM) oxidation of methane, which are important CH4 sinks in lakes. In contrast to marine benthic environments, our knowledge about the modes of AOM and the related methanotrophic microorganisms in anoxic lake sediments is still rudimentary. Here, we demonstrate the occurrence of AOM in the anoxic sediments of Lake Sempach (Switzerland), with maximum in situ AOM rates observed within the surface sediment layers in presence of multiple groups of methanotrophic bacteria and various oxidants known to support AOM. However, substrate-amended incubations (with NO2 -, NO3 -, SO4 2-, Fe-, and Mn-oxides) revealed that none of the electron acceptors previously reported to support AOM enhanced methane turnover in Lake Sempach sediments under anoxic conditions. In contrast, the addition of oxygen to the anoxic sediments resulted in an approximately 10-fold increase in methane oxidation relative to the anoxic incubations. Phylogenetic and isotopic evidence indicate that both Type I and Type II aerobic methanotrophs were growing on methane under both oxic and anoxic conditions, although methane assimilation rates were an order of magnitude higher under oxic conditions. While the anaerobic electron acceptor responsible for AOM could not be identified, these findings expand our understanding of the metabolic versatility of canonically aerobic methanotrophs under anoxic conditions, with important implications for future investigations to identify methane oxidation processes. Bacterial AOM by facultative aerobic methane oxidizers might be of much larger environmental significance in reducing methane emissions than previously thought.

Influence of aphotic haloclines and euxinia on organic biomarkers and microbial communities in a thalassohaline and alkaline volcanic crater lake

Studies on microbial communities, and their associated organic biomarkers, that are found thriving in the aphotic euxinic waters in modern stratified ecosystems are scarce compared to those undertaken in euxinic photic zones. The Dziani Dzaha (Mayotte, Indian Ocean) is a tropical, saline, alkaline crater lake that has recently been presented as a modern analog of Proterozoic Oceans due to its thalassohaline classification (having water of marine origin) and specific biogeochemical characteristics. Continuous intense photosynthetic production and microbial mineralization keep most of the water column permanently aphotic and anoxic preventing the development of a euxinic (sulfidic and anoxic) photic zone despite a high sulfide/sulfate ratio and the presence of permanent or seasonal haloclines. In this study, the molecular composition of the organic matter in Lake Dziani Dzaha was investigated and compared to the microbial diversity evaluated through 16S rRNA gene amplicon sequencing, over two contrasting seasons (rainy vs. dry) that influence water column stratification. Depth profiles of organic biomarker concentrations (chlorophyll-a and lipid biomarkers) and bacterial and archaeal OTU abundances appeared to be strongly dependent on the presence of aphotic haloclines and euxinia. OTU abundances revealed the importance of specific haloalkaliphilic bacterial and archaeal assemblages in phytoplanktonic biomass recycling and the biogeochemical functioning of the lake, suggesting new haloalkaline non-phototrophic anaerobic microbial precursors for some of the lipid biomarkers. Uncultured Firmicutes from the family Syntrophomonadaceae (Clostridiales), and Bacteroidetes from the ML635J-40 aquatic group, emerged as abundant chemotrophic bacterial members in the anoxic or euxinic waters and were probably responsible for the production of short-chain n-alkenes, wax esters, diplopterol, and tetrahymanol. Halocline-dependent euxinia also had a strong impact on the archaeal community which was dominated by Woesearchaeota in the sulfide-free waters. In the euxinic waters, methanogenic Euryarchaeota from the Methanomicrobia, Thermoplasmata, and WSA2 classes dominated and were likely at the origin of common hydrocarbon biomarkers of methanogens (phytane, pentamethyl-eicosenes, and partially hydrogenated squalene).

Lipidomic landscape in cancer: Actionable insights for membrane-based therapy and diagnoses

Cancer cells display altered cellular lipid metabolism, including disruption in endogenous lipid synthesis, storage, and exogenous uptake for membrane biogenesis and functions. Altered lipid metabolism and, consequently, lipid composition impacts cellular function by affecting membrane structure and properties, such as fluidity, rigidity, membrane dynamics, and lateral organization. Herein, we provide an overview of lipid membranes and how their properties affect cellular functions. We also detail how the rewiring of lipid metabolism impacts the lipidomic landscape of cancer cell membranes and influences the characteristics of cancer cells. Furthermore, we discuss how the altered cancer lipidome provides cues for developing lipid-inspired innovative therapeutic and diagnostic strategies while improving our limited understanding of the role of lipids in cancer initiation and progression. We also present the arcade of membrane characterization techniques to cement their relevance in cancer diagnosis and monitoring of treatment response.

Hepatic Lipidomics Analysis Reveals the Ameliorative Effects of Highland Barley β-Glucan on Western Diet-Induced Nonalcoholic Fatty Liver Disease Mice

Nonalcoholic fatty liver disease (NAFLD) is characterized by marked imbalances in lipid storage and metabolism. Because the beneficial health effects of cereal β-glucan (BG) include lowering cholesterol and regulating lipid metabolism, BG may alleviate the imbalances in lipid metabolism observed during NAFLD. The aim of our study was to investigate whether BG from highland barley has an effect on western diet-induced NAFLD in mice. Using lipidomics, we investigated the underlying mechanisms of BG intervention, and identified potential lipid biomarkers. The results reveal that BG (300 mg/kg body weight) significantly alleviated liver steatosis. Lipidomics analysis demonstrated that BG also altered lipid metabolic patterns. We were able to identify 13 differentially regulated lipid species that may be useful as lipid biomarkers. Several genes in the hepatic lipid and cholesterol metabolism pathways were also modulated. These findings provide evidence that BG ameliorates NAFLD by altering liver lipid metabolites and regulating lipid metabolism-related genes.

Nonalcoholic fatty liver disease stratification by liver lipidomics

Nonalcoholic fatty liver disease (NAFLD) is a common metabolic dysfunction leading to hepatic steatosis. However, NAFLD's global impact on the liver lipidome is poorly understood. Using high-resolution shotgun mass spectrometry, we quantified the molar abundance of 316 species from 22 major lipid classes in liver biopsies of 365 patients, including nonsteatotic patients with normal or excessive weight, patients diagnosed with NAFL (nonalcoholic fatty liver) or NASH (nonalcoholic steatohepatitis), and patients bearing common mutations of NAFLD-related protein factors. We confirmed the progressive accumulation of di- and triacylglycerols and cholesteryl esters in the liver of NAFL and NASH patients, while the bulk composition of glycerophospho- and sphingolipids remained unchanged. Further stratification by biclustering analysis identified sphingomyelin species comprising n24:2 fatty acid moieties as membrane lipid markers of NAFLD. Normalized relative abundance of sphingomyelins SM 43:3;2 and SM 43:1;2 containing n24:2 and n24:0 fatty acid moieties, respectively, showed opposite trends during NAFLD progression and distinguished NAFL and NASH lipidomes from the lipidome of nonsteatotic livers. Together with several glycerophospholipids containing a C22:6 fatty acid moiety, these lipids serve as markers of early and advanced stages of NAFL.

The role of lipids in exosome biology and intercellular communication: Function, analytics and applications

Exosomes are extracellular vesicles that in recent years have received special attention for their regulatory functions in numerous biological processes. Recent evidence suggests a correlation between the composition of exosomes in body fluids and the progression of some disorders, such as cancer, diabetes and neurodegenerative diseases. In consequence, numerous studies have been performed to evaluate the composition of these vesicles, aiming to develop new biomarkers for diagnosis and to find novel therapeutic targets. On their part, lipids represent one of the most important components of exosomes, with important structural and regulatory functions during exosome biogenesis, release, targeting and cellular uptake. Therefore, exosome lipidomics has emerged as an innovative discipline for the discovery of novel lipid species with biomedical applications. This review summarizes the current knowledge about exosome lipids and their roles in exosome biology and intercellular communication. Furthermore, it presents the state-of-the-art analytical procedures used in exosome lipidomics while emphasizing how this emerging discipline is providing new insights for future applications of exosome lipids in biomedicine.

Greenhouse gas production and lipid biomarker distribution in Yedoma and Alas thermokarst lake sediments in Eastern Siberia

Permafrost thaw leads to thermokarst lake formation and talik growth tens of meters deep, enabling microbial decomposition of formerly frozen organic matter (OM). We analyzed two 17-m-long thermokarst lake sediment cores taken in Central Yakutia, Russia. One core was from an Alas lake in a Holocene thermokarst basin that underwent multiple lake generations, and the second core from a young Yedoma upland lake (formed ~70 years ago) whose sediments have thawed for the first time since deposition. This comparison provides a glance into OM fate in thawing Yedoma deposits. We analyzed total organic carbon (TOC) and dissolved organic carbon (DOC) content, n-alkane concentrations, and bacterial and archaeal membrane markers. Furthermore, we conducted 1-year-long incubations (4°C, dark) and measured anaerobic carbon dioxide (CO₂ ) and methane (CH₄ ) production. The sediments from both cores contained little TOC (0.7 ± 0.4 wt%), but DOC values were relatively high, with the highest values in the frozen Yedoma lake sediments (1620 mg L^-1 ). Cumulative greenhouse gas (GHG) production after 1 year was highest in the Yedoma lake sediments (226 ± 212 µg CO₂ -C g^-1  dw, 28 ± 36 µg CH₄ -C g^-1  dw) and 3 and 1.5 times lower in the Alas lake sediments, respectively (75 ± 76 µg CO₂ -C g^-1  dw, 19 ± 29 µg CH₄ -C g^-1  dw). The highest CO₂ production in the frozen Yedoma lake sediments likely results from decomposition of readily bioavailable OM, while highest CH₄ production in the non-frozen top sediments of this core suggests that methanogenic communities established upon thaw. The lower GHG production in the non-frozen Alas lake sediments resulted from advanced OM decomposition during Holocene talik development. Furthermore, we found that drivers of CO₂ and CH₄ production differ following thaw. Our results suggest that GHG production from TOC-poor mineral deposits, which are widespread throughout the Arctic, can be substantial. Therefore, our novel data are relevant for vast ice-rich permafrost deposits vulnerable to thermokarst formation.

Characterization of brain-derived extracellular vesicle lipids in Alzheimer's disease

Lipid dyshomeostasis is associated with the most common form of dementia, Alzheimer's disease (AD). Substantial progress has been made in identifying positron emission tomography and cerebrospinal fluid biomarkers for AD, but they have limited use as front-line diagnostic tools. Extracellular vesicles (EVs) are released by all cells and contain a subset of their parental cell composition, including lipids. EVs are released from the brain into the periphery, providing a potential source of tissue and disease specific lipid biomarkers. However, the EV lipidome of the central nervous system is currently unknown and the potential of brain-derived EVs (BDEVs) to inform on lipid dyshomeostasis in AD remains unclear. The aim of this study was to reveal the lipid composition of BDEVs in human frontal cortex, and to determine whether BDEVs have an altered lipid profile in AD. Using semi-quantitative mass spectrometry, we describe the BDEV lipidome, covering four lipid categories, 17 lipid classes and 692 lipid molecules. BDEVs were enriched in glycerophosphoserine (PS) lipids, a characteristic of small EVs. Here we further report that BDEVs are enriched in ether-containing PS lipids, a finding that further establishes ether lipids as a feature of EVs. BDEVs in the AD frontal cortex offered improved detection of dysregulated lipids in AD over global lipid profiling of this brain region.  AD BDEVs had significantly altered glycerophospholipid and sphingolipid levels, specifically increased plasmalogen glycerophosphoethanolamine and decreased polyunsaturated fatty acyl containing lipids, and altered amide-linked acyl chain content in sphingomyelin and ceramide lipids relative to CTL. The most prominent alteration was a two-fold decrease in lipid species containing anti-inflammatory/pro-resolving docosahexaenoic acid. The in-depth lipidome analysis provided in this study highlights the advantage of EVs over more complex tissues for improved detection of dysregulated lipids that may serve as potential biomarkers in the periphery.

The Emerging World of Membrane Vesicles: Functional Relevance, Theranostic Avenues and Tools for Investigating Membrane Function

Lipids are essential components of cell membranes and govern various membrane functions. Lipid organization within membrane plane dictates recruitment of specific proteins and lipids into distinct nanoclusters that initiate cellular signaling while modulating protein and lipid functions. In addition, one of the most versatile function of lipids is the formation of diverse lipid membrane vesicles for regulating various cellular processes including intracellular trafficking of molecular cargo. In this review, we focus on the various kinds of membrane vesicles in eukaryotes and bacteria, their biogenesis, and their multifaceted functional roles in cellular communication, host-pathogen interactions and biotechnological applications. We elaborate on how their distinct lipid composition of membrane vesicles compared to parent cells enables early and non-invasive diagnosis of cancer and tuberculosis, while inspiring vaccine development and drug delivery platforms. Finally, we discuss the use of membrane vesicles as excellent tools for investigating membrane lateral organization and protein sorting, which is otherwise challenging but extremely crucial for normal cellular functioning. We present current limitations in this field and how the same could be addressed to propel a fundamental and technology-oriented future for extracellular membrane vesicles.

Understanding the geobiology of the terminal Ediacaran Khatyspyt Lagerstätte (Arctic Siberia, Russia)

The Khatyspyt Lagerstätte (~544 Ma, Russia) provides a valuable window into late Ediacaran Avalon-type ecosystems with rangeomorphs, arboreomorphs, and mega-algae. Here, we tackle the geobiology of this Lagerstätte by the combined analysis of paleontological features, sedimentary facies, and lipid biomarkers. The Khatyspyt Formation was deposited in carbonate ramp environments. Organic matter (0.12-2.22 wt.% TOC) displays characteristic Ediacaran biomarker features (e.g., eukaryotic steranes dominated by the C₂₉ stigmastane). Some samples contain a putative 2-methylgammacerane that was likely sourced by ciliates and/or bacteria. 24-isopropylcholestane and 26-methylstigmastane are consistently scarce (≤0.4% and ≤0.2% of ∑C_27-30 regular steranes, respectively). Thus, Avalon-type organisms occupied different niches than organisms capable of directly synthesizing C₃₀ sterane precursors among their major lipids. Relative abundances of eukaryotic steranes and bacterial hopanes (sterane/hopane ratios = 0.07-0.30) demonstrate oligotrophic and bacterially dominated marine environments, similar to findings from other successions with Ediacara-type fossils. Ediacara-type fossils occur in facies characterized by microbial mats and biomarkers indicative for a stratified marine environment with normal-moderate salinities (moderate-high gammacerane index of 2.3-5.7; low C₃₅ homohopane index of 0.1-0.2). Mega-algae, in contrast, are abundant in facies that almost entirely consist of allochthonous event layers. Biomarkers in these samples indicate a non-stratified marine environment and normal salinities (low gammacerane index of 0.6-0.8; low C₃₅ homohopane index of 0.1). Vertical burrowers occur in similar facies but with biomarker evidence for stratification in the water column or around the seafloor (high gammacerane index of 5.6). Thus, the distribution of macro-organisms and burrowers was controlled by various, dynamically changing environmental factors. It appears likely that dynamic settings like the Khatyspyt Lagerstätte provided metabolic challenges for sustenance and growth which primed eukaryotic organisms to cope with changing environmental habitats, allowing for a later diversification and expansion of complex macroscopic life in the marine realm.

Antineoplastic Agents Targeting Sphingolipid Pathways

Emerging studies in the enigmatic area of bioactive lipids have made many exciting new discoveries in recent years. Once thought to play a strictly structural role in cellular function, it has since been determined that sphingolipids and their metabolites perform a vast variety of cellular functions beyond what was previously believed. Of utmost importance is their role in cellular signaling, for it is now well understood that select sphingolipids serve as bioactive molecules that play critical roles in both cancer cell death and survival, as well as other cellular responses such as chronic inflammation, protection from intestinal pathogens, and intrinsic protection from intestinal contents, each of which are associated with oncogenesis. Importantly, it has been demonstrated time and time again that many different tumors display dysregulation of sphingolipid metabolism, and the exact profile of said dysregulation has been proven to be useful in determining not only the presence of a tumor, but also the susceptibility to various chemotherapeutic drugs, as well as the metastasizing characteristics of the malignancies. Since these discoveries surfaced it has become apparent that the understanding of sphingolipid metabolism and profile will likely become of great importance in the clinic for both chemotherapy and diagnostics of cancer. The goal of this paper is to provide a comprehensive review of the current state of chemotherapeutic agents that target sphingolipid metabolism that are undergoing clinical trials. Additionally, we will formulate questions involving the use of sphingolipid metabolism as chemotherapeutic targets in need of further research.

Common and Differential Traits of the Membrane Lipidome of Colon Cancer Cell Lines and their Secreted Vesicles: Impact on Studies Using Cell Lines

Colorectal cancer (CRC) is the fourth leading cause of cancer death in the world. Despite the screening programs, its incidence in the population below the 50s is increasing. Therefore, new stratification protocols based on multiparametric approaches are highly needed. In this scenario, the lipidome is emerging as a powerful tool to classify tumors, including CRC, wherein it has proven to be highly sensitive to cell malignization. Hence, the possibility to describe the lipidome at the level of lipid species has renewed the interest to investigate the role of specific lipid species in pathologic mechanisms, being commercial cell lines, a model still heavily used for this purpose. Herein, we characterize the membrane lipidome of five commercial colon cell lines and their extracellular vesicles (EVs). The results demonstrate that both cell and EVs lipidome was able to segregate cells according to their malignancy. Furthermore, all CRC lines shared a specific and strikingly homogenous impact on ether lipid species. Finally, this study also cautions about the need of being aware of the singularities of each cell line at the level of lipid species. Altogether, this study firmly lays the groundwork of using the lipidome as a solid source of tumor biomarkers.

Free and kerogen-bound biomarkers from late Tonian sedimentary rocks record abundant eukaryotes in mid-Neoproterozoic marine communities

Lipid biomarker assemblages preserved within the bitumen and kerogen phases of sedimentary rocks from the ca. 780-729 Ma Chuar and Visingsö Groups facilitate paleoenvironmental reconstructions and reveal fundamental aspects of emerging mid-Neoproterozoic marine communities. The Chuar and Visingsö Groups were deposited offshore of two distinct paleocontinents (Laurentia and Baltica, respectively) during the Tonian Period, and the rock samples used had not undergone excessive metamorphism. The major polycyclic alkane biomarkers detected in the rock bitumens and kerogen hydropyrolysates consist of tricyclic terpanes, hopanes, methylhopanes, and steranes. Major features of the biomarker assemblages include detectable and significant contribution from eukaryotes, encompassing the first robust occurrences of kerogen-bound regular steranes from Tonian rocks, including 21-norcholestane, 27-norcholestane, cholestane, ergostane, and cryostane, along with a novel unidentified C₃₀ sterane series from our least thermally mature Chuar Group samples. Appreciable values for the sterane/hopane (S/H) ratio are found for both the free and kerogen-bound biomarker pools for both the Chuar Group rocks (S/H between 0.09 and 1.26) and the Visingsö Group samples (S/H between 0.03 and 0.37). The more organic-rich rock samples generally yield higher S/H ratios than for organic-lean substrates, which suggests a marine nutrient control on eukaryotic abundance relative to bacteria. A C₂₇ sterane (cholestane) predominance among total C₂₆ -C₃₀ steranes is a common feature found for all samples investigated, with lower amounts of C₂₈ steranes (ergostane and crysotane) also present. No traces of known ancient C₃₀ sterane compounds; including 24-isopropylcholestanes, 24-n-propylcholestanes, or 26-methylstigmastanes, are detectable in any of these pre-Sturtian rocks. These biomarker characteristics support the view that the Tonian Period was a key interval in the history of life on our planet since it marked the transition from a bacterially dominated marine biosphere to an ocean system which became progressively enriched with eukaryotes. The eukaryotic source organisms likely encompassed photosynthetic primary producers, marking a rise in red algae, and consumers in a revamped trophic structure predating the Sturtian glaciation.

Constraining the formation of authigenic carbonates in a seepage-affected cold-water coral mound by lipid biomarkers

Cold-water coral (CWC) mounds are build-ups comprised of coral-dominated intervals alternating with a mixed carbonate-siliciclastic matrix. At some locations, CWC mounds are influenced by methane seepage, but the impact of methane on CWC mounds is poorly understood. To constrain the potential impact of methane on CWC mound growth, lipid biomarker investigations were combined with mineralogical and petrographic analyses to investigate the anaerobic oxidation of methane (AOM) and authigenic carbonate formation in sediment from a seep-affected CWC mound in the Gulf of Cadiz. The occurrence of AOM was confirmed by characteristic lipids found within a semi-lithified zone (SLZ) consisting of authigenic aragonite, high-magnesium calcite and calcium-excess dolomite. The formation of high-Mg calcite is attributed to AOM, acting as a lithifying agent. Aragonite is only a minor phase. Ca-excess dolomite in the SLZ and upper parts may be formed by organoclastic sulphate reduction, favouring precipitation by increased alkalinity. The AOM biomarkers in the SLZ include isoprenoid-based archaeal membrane lipids, such as abundant glycerol dibiphytanyl glycerol tetraethers (GDGTs) dominated by GDGT-2. The δ¹³ C values of GDGT-2, measured as ether-cleaved monocyclic biphytanes, are as low as -100‰ versus V-PDB. Further, bacterial dialkyl glycerol diethers with two anteiso-C₁₅ alkyl chains and δ¹³ C values of -81‰ are interpreted as biomarkers of sulphate-reducing bacteria. The lipid biomarker signatures and mineralogical patterns suggest that anaerobic methane-oxidizing archaea of the ANME-1 group thrived in the subsurface at times of slow and diffusive methane seepage. Petrographic analyses revealed that the SLZ was exhumed at some point (e.g. signs of bioerosion of the semi-lithified sediment), providing a hard substrate for CWC larval settlement. In addition, this work reveals that AOM-induced semi-lithification likely played a role in mound stabilization. Lipid biomarker analysis proves to be a powerful tool to disentangle early diagenetic processes induced by microbial metabolisms.

Particulate Organic Matter Dynamics in a Permafrost Headwater Stream and the Kolyma River Mainstem

Ongoing rapid arctic warming leads to extensive permafrost thaw, which in turn increases the hydrologic connectivity of the landscape by opening up subsurface flow paths. Suspended particulate organic matter (POM) has proven useful to trace permafrost thaw signals in arctic rivers, which may experience higher organic matter loads in the future due to expansion and increasing intensity of thaw processes such as thermokarst and river bank erosion. Here we focus on the Kolyma River watershed in Northeast Siberia, the world's largest watershed entirely underlain by continuous permafrost. To evaluate and characterize the present-day fluvial release of POM from permafrost thaw, we collected water samples every 4-7 days during the 4-month open water season in 2013 and 2015 from the lower Kolyma River mainstem and from a small nearby headwater stream (Y3) draining an area completely underlain by Yedoma permafrost (Pleistocene ice- and organic-rich deposits). Concentrations of particulate organic carbon generally followed the hydrograph with the highest concentrations during the spring flood in late May/early June. For the Kolyma River, concentrations of dissolved organic carbon showed a similar behavior, in contrast to the headwater stream, where dissolved organic carbon values were generally higher and particulate organic carbon concentrations lower than for Kolyma. Carbon isotope analysis (δ13C, Δ14C) suggested Kolyma-POM to stem from both contemporary and older permafrost sources, while Y3-POM was more strongly influenced by in-stream production and recent vegetation. Lipid biomarker concentrations (high-molecular-weight n-alkanoic acids and n-alkanes) did not display clear seasonal patterns, yet implied Y3-POM to be more degraded than Kolyma-POM.

Regional diversity in subsistence among early farmers in Southeast Europe revealed by archaeological organic residues

The spread of early farming across Europe from its origins in Southwest Asia was a culturally transformative process which took place over millennia. Within regions, the pace of the transition was probably related to the particular climatic and environmental conditions encountered, as well as the nature of localized hunter-gatherer and farmer interactions. The establishment of farming in the interior of the Balkans represents the first movement of Southwest Asian livestock beyond their natural climatic range, and widespread evidence now exists for early pottery being used extensively for dairying. However, pottery lipid residues from sites in the Iron Gates region of the Danube in the northern Balkans show that here, Neolithic pottery was being used predominantly for processing aquatic resources. This stands out not only within the surrounding region but also contrasts markedly with Neolithic pottery use across wider Europe. These findings provide evidence for the strategic diversity within the wider cultural and economic practices during the Neolithic, with this exceptional environmental and cultural setting offering alternative opportunities despite the dominance of farming in the wider region.

Novel sphingomyelin biomarkers for brain glioma and associated regulation research on the PI3K/Akt signaling pathway

Glioma is one of the most common malignant tumor types of the central nervous system. It is necessary to identify biomarkers and novel therapeutic targets for glioma. The purpose of the present study was to distinguish lipid biomarkers with differential expression patterns in glioma tissues and normal brain tissues by matrix assisted laser desorption/ionization (MALDI)-imaging and MALDI-time of flight (TOF)-mass spectrometry (MS). Additionally, identification of lipid biomarkers was performed to describe novel therapeutic targets for glioma treatment. A total of six tissues from three patients with glioma and three control patients with traumatic brain injury were analyzed using UltrafleXtreme MALDI-TOF/TOF. The expression levels of 15 lipid peaks were higher in the TBT samples compared with in the GBT samples. The expression levels of another 16 lipid peaks were higher in the GBT samples compared with in the TBT samples. 14 peaks were identified as sphingomyelins using MS/MS. Additional results were also obtained from experiments using the glioma cell line U373-MG. These results indicated that treatment with the drug desipramine (Desi) inhibited the accumulation of ceramide on the cell membranes of glioma U373-MG cells. Treatment with Desi inhibited the activation of insulin-like growth factor-1 receptor and inhibited the activation of proteins in the PI3K/Akt signaling pathway.

Leaf wax n-alkane patterns of six tropical montane tree species show species-specific environmental response

It remains poorly understood how the composition of leaf wax n-alkanes reflects the local environment. This knowledge gap inhibits the interpretation of plant responses to the environment at the community level and, by extension, inhibits the applicability of n-alkane patterns as a proxy for past environments. Here, we studied the n-alkane patterns of five Miconia species and one Guarea species, in the Ecuadorian Andes (653-3,507 m a.s.l.). We tested for species-specific responses in the average chain length (ACL), the C31/(C31 + C29) ratio (ratio), and individual odd n-alkane chain lengths across an altitudinally driven environmental gradient (mean annual temperature, mean annual relative air humidity, and mean annual precipitation). We found significant correlations between the environmental gradients and species-specific ACL and ratio, but with varying magnitude and direction. We found that the n-alkane patterns are species-specific at the individual chain length level, which could explain the high variance in metrics like ACL and ratio. Although we find species-specific sensitivity and responses in leaf n-alkanes, we also find a general decrease in "shorter" (C31) chain lengths with the environmental gradients, most strongly with temperature, suggesting n-alkanes are useful for reconstructing past environments.

Maternal Experience of Domestic Violence, Associations with Children's Lipid Biomarkers at 10 Years: Findings from MINIMat Study in Rural Bangladesh

The consequences of maternal experience of Domestic Violence (DV) on their children’s cardio-metabolic risk factors are unclear. We aimed to assess if maternal exposure to any or a specific form of DV (i.e., physical, sexual, emotional and controlling behaviors) before and after childbirth was associated with their children’s lipid biomarkers at the age of 10 years. A current observational sub-study of a larger MINIMat trial included a cohort of 1167 mothers and their children. The conflict tactic scale was used to record women’s experience of lifetime DV before and after childbirth at week 30 of pregnancy and at a 10-year follow up, respectively. Five ml of fasting blood sample was collected from the children to evaluate their lipid profile. Children of women who experienced any DV before childbirth had lower Apo A (β_adj −0.04; 95% CI: −0.08, −0.01). Women who experienced physical DV both before and after childbirth had children with higher triglycerides (β_adj 0.07; 95% CI: 0.01, 0.14). Children whose mother experienced sexual DV before birth had lower Apo A (β_adj −0.05; 95% CI: −0.08, −0.01) and High Density Lipoprotein (HDL) (β_adj −0.05; 95% CI: −0.10, −0.01) as well as higher Low Density Lipoprotein (LDL) (β_adj 0.17; 95% CI: 0.05, 0.29) and LDL/HDL (β 0.24; 95% CI: 0.11, 0.38). However, levels of LDL (β_adj −0.17; 95% CI: −0.28, −0.06), LDL/HDL (β_adj −0.12; 95% CI: −0.25, −0.00) and cholesterol (β_adj −0.13; 95% CI: −0.25, −0.02) were lower among the children of mothers who experienced controlling behavior after childbirth. Results from the current study suggest that maternal experience of physical or sexual DV might negatively affect their children’s lipid profile at the age of 10 years.

Microbial Biomarker Transition in High-Altitude Sinter Mounds From El Tatio (Chile) Through Different Stages of Hydrothermal Activity

Geothermal springs support microbial communities at elevated temperatures in an ecosystem with high preservation potential that makes them interesting analogs for early evolution of the biogeosphere. The El Tatio geysers field in the Atacama Desert has astrobiological relevance due to the unique occurrence of geothermal features with steep hydrothermal gradients in an otherwise high altitude, hyper-arid environment. We present here results of our multidisciplinary field and molecular study of biogeochemical evidence for habitability and preservation in silica sinter at El Tatio. We sampled three morphologically similar geyser mounds characterized by differences in water activity (i.e., episodic liquid water, steam, and inactive geyser lacking hydrothermal activity). Multiple approaches were employed to determine (past and present) biological signatures and dominant metabolism. Lipid biomarkers indicated relative abundance of thermophiles (dicarboxylic acids) and sulfate reducing bacteria (branched carboxylic acids) in the sinter collected from the liquid water mound; photosynthetic microorganisms such as cyanobacteria (alkanes and isoprenoids) in the steam sinter mound; and archaea (squalane and crocetane) as well as purple sulfur bacteria (cyclopropyl acids) in the dry sinter from the inactive geyser. The three sinter structures preserved biosignatures representative of primary (thermophilic) and secondary (including endoliths and environmental contaminants) microbial communities. Sequencing of environmental 16S rRNA genes and immuno-assays generally corroborated the lipid-based microbial identification. The multiplex immunoassays and the compound-specific isotopic analysis of carboxylic acids, alkanols, and alkanes indicated that the principal microbial pathway for carbon fixation in the three sinter mounds was through the Calvin cycle, with a relative larger contribution of the reductive acetyl-CoA pathway in the dry system. Other inferred metabolic traits varied from the liquid mound (iron and sulfur chemistry), to the steam mound (nitrogen cycle), to the dry mound (perchlorate reduction). The combined results revealed different stages of colonization that reflect differences in the lifetime of the mounds, where primary communities dominated the biosignatures preserved in sinters from the still active geysers (liquid and steam mounds), in contrast to the surviving metabolisms and microbial communities at the end of lifetime of the inactive geothermal mound.

A stable and productive marine microbial community was sustained through the end-Devonian Hangenberg Crisis within the Cleveland Shale of the Appalachian Basin, United States

The end-Devonian Hangenberg Crisis constituted one of the greatest ecological and environmental perturbations of the Paleozoic Era. To date, however, it has been difficult to precisely constrain the occurrence of the Hangenberg Crisis in the Appalachian Basin of the United States and thus to directly assess the effects of this crisis on marine microbial communities and paleoenvironmental conditions. Here, we integrate organic and inorganic chemostratigraphic records compiled from two discrete outcrop locations to characterize the onset and paleoenvironmental transitions associated with the Hangenberg Crisis within the Cleveland Shale member of the Ohio Shale. The upper Cleveland Shale records both positive carbon (δ¹³ C_org ) and nitrogen (δ¹⁵ N_total ) isotopic excursions, and replenished trace metal inventories with links to eustatic rise. These dual but apparently temporally offset isotope excursions may be useful for stratigraphic correlation with other productive end-Devonian epeiric marine locations. Deposition of the black shale succession occurred locally beneath a redox-stratified water column with euxinic zones, with signs of strengthening denitrification during the Hangenberg Crisis interval, but with an otherwise stable and algal-rich marine microbial community structure sustained in the surface mixed layer as ascertained by lipid biomarker assemblages. Discernible trace fossil signals in some horizons suggest, however, that bioturbation and seafloor oxygenation occurred episodically throughout this succession and highlight that geochemical proxies often fail to capture these rapid and sporadic redox fluctuations in ancient black shales. The paleoenvironmental conditions, source biota, and accumulations of black shale are consistent with expressions of the Hangenberg Crisis globally, suggesting this event is likely captured within the uppermost strata of the Cleveland Shale in North America.

Microbial diversity and biomarker analysis of modern freshwater microbialites from Laguna Bacalar, Mexico

Laguna Bacalar is a sulfate-rich freshwater lake on the Yucatan Peninsula that hosts large microbialites. High sulfate concentrations distinguish Laguna Bacalar from other freshwater microbialite sites such as Pavilion Lake and Alchichica, Mexico, as well as from other aqueous features on the Yucatan Peninsula. While cyanobacterial populations have been described here previously, this study offers a more complete characterization of the microbial populations and corresponding biogeochemical cycling using a three-pronged geobiological approach of microscopy, high-throughput DNA sequencing, and lipid biomarker analyses. We identify and compare diverse microbial communities of Alphaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria that vary with location along a bank-to-bank transect across the lake, within microbialites, and within a neighboring mangrove root agglomeration. In particular, sulfate-reducing bacteria are extremely common and diverse, constituting 7%-19% of phylogenetic diversity within the microbialites, and are hypothesized to significantly influence carbonate precipitation. In contrast, Cyanobacteria account for less than 1% of phylogenetic diversity. The distribution of lipid biomarkers reflects these changes in microbial ecology, providing meaningful biosignatures for the microbes in this system. Polysaturated short-chain fatty acids characteristic of cyanobacteria account for <3% of total abundance in Laguna Bacalar microbialites. By contrast, even short-chain and monounsaturated short-chain fatty acids attributable to both Cyanobacteria and many other organisms including types of Alphaproteobacteria and Gammaproteobacteria constitute 43%-69% and 17%-25%, respectively, of total abundance in microbialites. While cyanobacteria are the largest and most visible microbes within these microbialites and dominate the mangrove root agglomeration, it is clear that their smaller, metabolically diverse associates are responsible for significant biogeochemical cycling in this microbialite system.

The Role of Lipid Biomarkers in Major Depression

In the UK, the lifetime-documented prevalence of major depressive disorder (MDD) is currently 10%. Despite its increasing prevalence and devastating impact on quality of life, the pathophysiological mechanisms underpinning MDD remain to be fully elucidated. Current theories of neurobiological components remain incomplete and protein-centric, rendering pharmacological treatment options suboptimal. In this review, we highlight the pivotal role of lipids in intra- and inter-neuronal functioning, emphasising the potential use of lipids as biomarkers for MDD. The latter has significant implications for improving our understanding of MDD at the cellular and circuit level. There is particular focus on cholesterol (high and low density lipoprotein), omega-3, and omega-6 polyunsaturated fatty acids due to established evidence in the literature of a link between atherosclerotic disease and major depression. We argue that there is significant potential scope for the use of such peripheral biomarkers in the diagnosis, stratification and treatment of MDD.

Transhydrogenase and Growth Substrate Influence Lipid Hydrogen Isotope Ratios in Desulfovibrio alaskensis G20

Microbial fatty acids preserve metabolic and environmental information in their hydrogen isotope ratios (²H/¹H). This ratio is influenced by parameters that include the ²H/¹H of water in the microbial growth environment, and biosynthetic fractionations between water and lipid. In some microbes, this biosynthetic fractionation has been shown to vary systematically with central energy metabolism, and controls on fatty acid ²H/¹H may be linked to the intracellular production of NADPH. We examined the apparent fractionation between media water and the fatty acids produced by Desulfovibrio alaskensis G20. Growth was in batch culture with malate as an electron donor for sulfate respiration, and with pyruvate and fumarate as substrates for fermentation and for sulfate respiration. A larger fractionation was observed as a consequence of respiratory or fermentative growth on pyruvate than growth on fumarate or malate. This difference correlates with opposite apparent flows of electrons through the electron bifurcating/confurcating transhydrogenase NfnAB. When grown on malate or fumarate, mutant strains of D. alaskensis G20 containing transposon disruptions in a copy of nfnAB show different fractionations than the wild type strain. This phenotype is muted during fermentative growth on pyruvate, and it is absent when pyruvate is a substrate for sulfate reduction. All strains and conditions produced similar fatty acid profiles, and the ²H/¹H of individual lipids changed in concert with the mass-weighted average. Unsaturated fatty acids were generally depleted in ²H relative to their saturated homologs, and anteiso-branched fatty acids were generally depleted in ²H relative to straight-chain fatty acids. Fractionation correlated with growth rate, a pattern that has also been observed in the fractionation of sulfur isotopes during dissimilatory sulfate reduction by sulfate-reducing bacteria.

Identification and quantitation of lipid C=C location isomers: A shotgun lipidomics approach enabled by photochemical reaction

The field of lipidomics has been significantly advanced by mass spectrometric analysis. The distinction and quantitation of the unsaturated lipid isomers, however, remain a long-standing challenge. In this study, we have developed an analytical tool for both identification and quantitation of lipid C=C location isomers from complex mixtures using online Paternò-Büchi reaction coupled with tandem mass spectrometry (MS/MS). The potential of this method has been demonstrated with an implementation into shotgun lipid analysis of animal tissues. Among 96 of the unsaturated fatty acids and glycerophospholipids identified from rat brain tissue, 50% of them were found as mixtures of C=C location isomers; for the first time, to our knowledge, the quantitative information of lipid C=C isomers from a broad range of classes was obtained. This method also enabled facile cross-tissue examinations, which revealed significant changes in C=C location isomer compositions of a series of fatty acids and glycerophospholipid (GP) species between the normal and cancerous tissues.

Lipidomics applications for disease biomarker discovery in mammal models

Lipidomics is a lipid-targeted metabolomics approach focusing on comprehensive analysis of all lipids with which they interact in biology systems. Recent technological advances in MS and chromatography have greatly enhanced the developments and applications of metabolic profiling of diverse lipids in complex biological samples. Lipidomics will not only provide insights into the specific functions of lipid species in health and disease, but will also identify potential biomarkers for establishing preventive or therapeutic programs for human disease. In this review, recent applications of lipidomics to understand animal models of disease such as metabolic syndromes, neurodegenerative diseases, cancer and infectious diseases are considered. We also discuss the lipidomics for the future perspectives and their potential problems.

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite-calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 ± 4.3 °C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite-calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in (13)C (δ(13)C(TOC) = -19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.

Do n-alkane biomarkers in soils/sediments reflect the δ²H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

During the last decade compound-specific deuterium ((2)H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ(2)H of precipitation (δ(2)H(prec)). Recently, several authors suggested that δ(2)H of n-alkanes (δ(2)H(n-alkanes)) can also be used as a proxy in paleoaltimetry studies. Here, we present results from a δ(2)H transect study (∼1500 to 4000 m above sea level [a.s.l.]) carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ(2)H(prec) is present above ∼2000 m a.s.l., that is, δ(2)H(prec) values become more negative with increasing altitude. The compound-specific δ(2)H values of nC27 and nC29 do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers) and the Ah-horizons (mineral topsoils). Although our δ(2)H(n-alkane) results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro [Peterse F, van der Meer M, Schouten S, Jia G, Ossebaar J, Blokker J, Sinninghe Damsté J. Assessment of soil n-alkane δD and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction. Biogeosciences. 2009;6:2799-2807], a re-interpretation is required given that the δ(2)H(n-alkane) results do not reflect the δ(2)H(prec) results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with the transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78% in ∼2000 m a.s.l. to 51% in 4000 m a.s.l.), strongly controls δ(2)H(leaf water). The modelled (2)H leaf water enrichment along the altitudinal transect matches well the measured (2)H leaf water enrichment as assessed by using the δ(2)H(prec) and δ(2)H(n-alkane) results and biosynthetic fractionation during n-alkane biosynthesis in leaves. Given that our results clearly demonstrate that n-alkanes in soils do not simply reflect δ(2)H(prec) but rather δ(2)H(leaf water), we conclude that care has to be taken not to over-interpret δ(2)H(n-alkane) records from soils and sediments when reconstructing δ(2)H of paleoprecipitation. Both in paleoaltimetry and in paleoclimate studies changes in relative humidity and consequently in δ(2)H(n-alkane) values can completely mask altitudinally or climatically controlled changes in δ(2)H(prec).