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Metabolites exuded by primary producers comprise a significant fraction of marine dissolved organic matter, a poorly characterized, heterogenous mixture that dictates microbial metabolism and biogeochemical cycling. We present a foundational untargeted molecular analysis of exudates released by coral reef primary producers using liquid chromatography-tandem mass spectrometry to examine compounds produced by two coral species and three types of algae (macroalgae, turfing microalgae, and crustose coralline algae [CCA]) from Moorea, French Polynesia. Of 10,568 distinct ion features recovered from reef and mesocosm waters, 1,667 were exuded by producers; the majority (86%) were organism specific, reflecting a clear divide between coral and algal exometabolomes. These data allowed us to examine two tenets of coral reef ecology at the molecular level. First, stoichiometric analyses show a significantly reduced nominal carbon oxidation state of algal exometabolites than coral exometabolites, illustrating one ecological mechanism by which algal phase shifts engender fundamental changes in the biogeochemistry of reef biomes. Second, coral and algal exometabolomes were differentially enriched in organic macronutrients, revealing a mechanism for reef nutrient-recycling. Coral exometabolomes were enriched in diverse sources of nitrogen and phosphorus, including tyrosine derivatives, oleoyl-taurines, and acyl carnitines. Exometabolites of CCA and turf algae were significantly enriched in nitrogen with distinct signals from polyketide macrolactams and alkaloids, respectively. Macroalgal exometabolomes were dominated by nonnitrogenous compounds, including diverse prenol lipids and steroids. This study provides molecular-level insights into biogeochemical cycling on coral reefs and illustrates how changing benthic cover on reefs influences reef water chemistry with implications for microbial metabolism.

The marine nitrogen (N) cycle profoundly impacts global ocean productivity. Amid rising deoxygenation in marine environments due to anthropogenic pressures, understanding the impact of this on the marine N-cycle is vital. The Black Sea's evolution from an oxygenated lacustrine basin to an anoxic marine environment over the last deglaciation and Holocene offers insight into these dynamics. Here, we generated records of the organic biomarkers heterocyte glycolipids, crenarchaeol, and bacteriohopanetetrol, associated with various water-column microbial N-cycle processes, which indicate a profound change in Black Sea N-cycle dynamics at ~ 7.2 ka when waters became severely deoxygenated. This transition substantially reduced Thaumarchaeota-driven nitrification and enhanced loss of bioavailable nitrogen through anammox. In contrast, other climatic changes over the last deglaciation and Holocene, such as freshwater input, water-level variations and temperature changes, did not impact these processes. Cyanobacterial nitrogen fixation in surface waters proved more responsive to changes in salinity and associated water column stratification. Our results indicate that future deoxygenation in marine environments may enhance bioavailable nitrogen loss by anammox and reduce nitrification by Thaumarchaeota, while enhanced stratification may increase cyanobacterial nitrogen fixation in the surface waters. [ABSTRACT FROM AUTHOR]

Understanding how microbial lipidomes adapt to environmental and nutrient stress is crucial for comprehending microbial survival and functionality. Certain anaerobic bacteria can synthesize glycerolipids with ether/ester bonds, yet the complexities of their lipidome remodeling under varying physicochemical and nutritional conditions remain largely unexplored. In this study, we thoroughly examined the lipidome adaptations of Desulfatibacillum alkenivorans strain PF2803T, a mesophilic anaerobic sulfate-reducing bacterium known for its high proportions of alkylglycerol ether lipids in its membrane, under various cultivation conditions including temperature, pH, salinity, and ammonium and phosphorous concentrations. Employing an extensive analytical and computational lipidomic methodology, we identified an assemblage of nearly 400 distinct lipids, including a range of glycerol ether/ester lipids with various polar head groups. Information theory-based analysis revealed that temperature fluctuations and phosphate scarcity profoundly influenced the lipidome's composition, leading to an enhanced diversity and specificity of novel lipids. Notably, phosphorous limitation led to the biosynthesis of novel glucuronosylglycerols and sulfur-containing aminolipids, termed butyramide cysteine glycerols, featuring various ether/ester bonds. This suggests a novel adaptive strategy for anaerobic heterotrophs to thrive under phosphorus-depleted conditions, characterized by a diverse array of nitrogen-and sulfur-containing polar head groups, moving beyond a reliance on conventional nonphospholipid types. [ABSTRACT FROM AUTHOR]

The California Current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the eastern North Pacific (ENP) OMZ, which is dissociated into subtropical and tropical regions (i.e. the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15 N over glacial–interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15 N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32° N, 118° W). Over the last two glacial terminations (∼ 160 kyr cal BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL 5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that (1) ladderanes were derived from anammox bacteria living within the ESTNP OMZ water column; (2) ladderanes were continuously present, with relatively high concentrations during both glacial and interglacial periods, showcasing that the ESTNP OMZ must have retained an anoxic core in which N loss occurred; and (3) anammox abundance appears to have been driven by both organic matter (OM) remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS, and it provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial–interglacial cycles. Lastly, ladderanes and their SC products were also detected in 160–500 kyr cal BP sediments (15.7–37.5 m b.s.f., metres below sea floor; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32°N; 118°W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160-500 cal ka BP sediments (15.7-37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

The Cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric C[O.sub.2] and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events (OAEs). Yet, the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained. Here we present a high-resolution record of sea-surface temperatures (SSTs) reconstructed using the [TEX.sub.86] paleothermometer for a sequence of early Aptian organic-rich sediments deposited during the first Cretaceous OAE (OAE1a) at Shatsky Rise in the tropical Pacific. SSTs range from ~30 to ~36[degrees]C and include two prominent cooling episodes of ~4 [degrees]C. The cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter. SST instability recorded during the early Aptian in the Pacific is comparable to that reported for the late AIbian-early Cenomanian in the Atlantic, suggesting that such climate perturbations may have recurred during the Cretaceous with concomitant consequences for biota and the marine environment. Keywords: [TEX.sub.86] index, oceanic anoxic events, Cretaceous sediments, carbon isotopes.

Paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy. A novel sea-surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota (the [TEX.sub.86]--tetraether index of tetraethers with 86 carbon atoms). Analysis of archaeal membrane lipids in core-top sediments from a diverse suite of lacustrine systems suggests the ubiquitous occurrence of low-temperature crenarchaeota in lake systems as well. Application of the [TEX.sub.86] proxy in these lacustrine systems indicates that it is valid in lake environments, and the calibration of TEXs6 in lacustrine systems is similar to that in the marine environment. This proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change. Keywords: paleothermometer, lacustrine sediments, climate change, continental climate, biomarkers.

The middle Cretaceous (125-88 Ma) greenhouse world was characterized by high atmospheric C[O.sub.2] levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both [delta][sup.18]O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on [delta][sup.18]O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the [delta][sup.18]O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., [TEX.sub.86] [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The [TEX.sub.86] proxy indicates that tropical SSTs in the proto--North Atlantic were at 32-36[degrees]C during the early Albian and late Cenomanian-early Turonian. This finding agrees with SST estimates based on [delta][sup.18]O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX86 proxy indicates cooler SSTs (27-32[degrees]C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on [delta][sup.18]O paleothermometry. Keywords: Cretaceous, sea-surface temperature, [TEX.sub.86], tropics.

Author(s): Jaap S. Sinninghe Damsté (corresponding author) [1]; Marc Strous [2]; W. Irene C. Rijpstra [1]; Ellen C. Hopmans [1]; Jan A. J. Geenevasen [3]; Adri C. T. van Duin [...]

Research has been conducted on the crenarchaeotes and glycerol dibiphytanyl tetraethers of hyperthermophilic archaea in water samples from the Arabian Sea. The results of the quantitative analysis of these bacteria are presented.