Deep subseafloor sediments host a microbial biosphere with unknown impact on global biogeochemical cycles. This study tests previous evidence based on microbial intact polar lipids (IPLs) as proxies ...of live biomass, suggesting that Archaea dominate the marine sedimentary biosphere. We devised a sensitive radiotracer assay to measure the decay rate of (¹⁴Cglucosyl)-diphytanylglyceroldiether (GlcDGD) as an analog of archaeal IPLs in continental margin sediments. The degradation kinetics were incorporated in model simulations that constrained the fossil fraction of subseafloor IPLs and rates of archaeal turnover. Simulating the top 1 km in a generic continental margin sediment column, we estimated degradation rate constants of GlcDGD being one to two orders of magnitude lower than those of bacterial IPLs, with half-lives of GlcDGD increasing with depth to 310 ky. Given estimated microbial community turnover times of 1.6-73 ky in sediments deeper than 1 m, 50-96% of archaeal IPLs represent fossil signals. Consequently, previous lipid-based estimates of global subseafloor biomass probably are too high, and the widely observed dominance of archaeal IPLs does not rule out a deep biosphere dominated by Bacteria. Reverse modeling of existing concentration profiles suggest that archaeal IPL synthesis rates decline from around 1,000 pg.mL⁻¹ sedimenty⁻¹ at the surface to 0.2 pg.mL⁻¹.y⁻¹ at 1 km depth, equivalent to production of 7 × 10⁵ to 140 archaeal cellsmL⁻¹ sediment.y⁻¹, respectively. These constraints on microbial growth are an important step toward understanding the relationship between the deep biosphere and the carbon cycle.
Alzheimer's disease (AD) is a multifactorial neurodegenerative disease, with a complex pathogenesis and an irreversible course. Therefore, the early diagnosis of AD is particularly important for the ...intervention, prevention, and treatment of the disease. Based on the different pathophysiological mechanisms of AD, the research progress of biofluid biomarkers are classified and reviewed. In the end, the challenges and perspectives of future research are proposed.
•IP GDGTs including 1G- and 2G-iso-GDGTs occur in the OMZ of the ETNP.•Core iso-GDGTs were most abundant of 9 groups core lipid.•TEX86 of IP and core iso-GDGTs had similar shape but different ...values.•IP GDGTs and OH-GDGTs were abundant in the upper OMZ, representing a living signal.•Other core lipids were more abundant in the mid OMZ.
The distributions of microbial glycerol ether lipids in suspended particulate matter in the oxygen minimum zone (OMZ) of the Eastern Tropical North Pacific Ocean (ETNP) were investigated. Nine groups of glycerol ether core lipids were detected and quantified: isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) (iso-GDGTs), isoprenoid glycerol dialkanol diethers (iso-GDDs) and hydroxylated isoprenoid GDGTs and GDDs (OH-GDGTs and OH-GDDs) of archaeal origin; branched glycerol dialkyl glycerol tetraethers (br-GDGTs) of bacterial origin and overly branched GDGTs (OB-GDGTs), sparsely branched GDGTs (SB-GDGTs), hybrid isoprenoid/branched GDGTs (IB-GDGTs) and a tentatively assigned H-shaped GDGT (H-1020) of unknown biological origin. The archaeal iso-GDGTs were the most abundant core lipids (89% of total), followed by iso-GDDs (4%), br-GDGTs (2%) and OH-GDGTs (1%). Archaeal intact polar GDGTs (IP GDGTs), including both mono- and diglycosidic iso-GDGTs, had depth profiles similar to OH-GDGTs and OH-GDDs, with a maximum concentration in the upper OMZ and secondary peaks in the mid and lower OMZ, suggesting similar but multiple planktonic sources. Core lipids of iso-GDGTs and other glycerol ethers showed deviating concentration profiles compared with IP GDGTs and OH-GDGTs and were most abundant in the mid OMZ. This is the first report of OH-GDDs, OB-GDGTs, SB-GDGTs, IB-GDGTs and H-1020 in the marine water column and the distribution patterns of these “orphan lipids” suggest that anaerobic planktonic microbes are their main source.
•Ethylene, ethanethiol and propanethiol stimulated production of the alkane.•Ethylene as substrate that gave the highest yield of alkane.•Methanogens were suggested to be involved in generation of ...the alkane.•H2 partial pressure required to stimulate ethanogenesis from ethylene was <0.01% H2.•Methanocalculus is a possible candidate for ethanogenesis from ethylene.
Ethane and propane are low molecular weight hydrocarbons observed widely at trace levels in cold marine sediments where thermogenic sources are considered insignificant, but their biological sources remain poorly constrained. In this study, several C2 and C3 compounds including alkenes, alcohols, thiols and carboxylic acids with a C2 or C3 skeleton were tested for their relative alkane-producing potential in an anoxic estuary sediment. Maximum conversion efficiency of substrates to ethane or propane was observed in the sediment supplemented with ethylene (up to 38%), followed by additions with ethanethiol (0.01%) and propanethiol (0.003%). Experiments with sterilized sediment, 2-bromoethanesulfonic acid or NaNO3 were negative for alkane production, suggesting that methanogens were involved in alkane generation. Detailed investigation on ethanogenesis from ethylene showed that this reaction required H2 but at reasonably low concentration (< 120nmol dissolved H2 l−1 slurry) and caused a slight stable carbon isotope effect (εethane/ethylene=−8.6±2.4‰). The high ethane-producing potential, reasonable H2 requirement and extensive occurrence of ethylene make ethylene reduction a plausible explanation for ethane in cold marine sediment. Phylogenetic analysis was first carried out with an ethane-producing enrichment with ethylene as the substrate and showed a dominance of homoacetogenic bacteria and the methanogenic genus Methanocalculus. Although we cannot rule out the possibility that other methanogens in the gene libraries are responsible for ethanogenesis from ethylene, the dominance of Methanocalculus, with its hydrogenotrophic cultured representatives, is in accord with our biogeochemical observation that H2 is required for this reaction.
Intact polar lipids (IPLs) are the main building blocks of cellular membranes and contain chemotaxonomic, ecophysiological and metabolic information, making them valuable biomarkers in microbial ...ecology and biogeochemistry. This study investigates IPLs in suspended particulate matter (SPM) in the water column of the eastern tropical North Pacific Ocean (ETNP), one of the most extensive open-ocean oxygen minimum zones (OMZs) in the world, with strong gradients of nutrients, temperature and redox conditions. A wide structural variety in polar lipid head-group composition and core structures exists along physical and geochemical gradients within the water column, from the oxygenated photic zone to the aphotic OMZ. We use this structural diversity in IPLs to evaluate the ecology and ecophysiological adaptations that affect organisms inhabiting the water column, especially the mid-depth OMZ in the context of biogeochemical cycles. Diacylglycerol phospholipids are present at all depths, but exhibit the highest relative abundance and compositional variety (including mixed acyl/ether core structures) in the upper and core OMZ where prokaryotic biomass was enriched. Surface ocean SPM is dominated by diacylglycerol glycolipids that are found in photosynthetic membranes. These and other glycolipids with varying core structures composed of ceramides and hydroxylated fatty acids are also detected with varying relative abundances in the OMZ and deep oxycline, signifying additional non-phototrophic bacterial sources for these lipids. Betaine lipids (with zero or multiple hydroxylations in the core structures) that are typically assigned to microalgae are found throughout the water column down to the deep oxycline but do not show a depth-related trend in relative abundance. Archaeal IPLs comprised of glycosidic and mixed glycosidic-phosphatidic glycerol dibiphytanyl glycerol tetraethers (GDGTs) are most abundant in the upper OMZ, where nitrate maxima point to ammonium oxidation but increase in relative abundance in the core OMZ and deep oxycline. The presence of non-phosphorus “substitute” lipids within the OMZ suggest that the indigenous microbes might be phosphorus limited (P starved) at ambient phosphate concentrations of 1 to 3.5 µM, although specific microbial sources for many of these lipids still remain unknown.
A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, salicylaldehyde and furfural. Solid lanthanum(III) complex of this ligand LaL(NO3)NO3-2H(2)0 have been prepared and ...characterized by elemental analyses, IR , UV and molar conductance .The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as : da/dt = A · e-ElRT. (1-a)² y The kinetic parameters(Δ, A), activation entropy ΔS* and activation free-energy ΔG* were also gained, E = 212.7 kJ/molΔlnLA =44.12, ℘S*=116.8 J/mol-KΔΔG*=148.1 kJ/mol
O641.4; A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine. o-vanillin and 2-hydroxy-l-naph-thaldehyde. Solid La (Ⅲ) complex of this ligand LaL(NO3)(NO3)·2H2O was prepared and ...characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage were studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=A·e-E/RT·(1-α)2. The kinetic parameters (E, A), activation entropy ΔS≠ and activation free-energy ΔG≠ were also gained.
In order to get a better understanding of microbes role in marine element cycles, organic-geochemical studies targeting microbial lipids and metabolic products in oxygen-deficient oceanic water ...column and sediments were carried out. Intact polar membrane lipids (IPLs) as biomarker for living biomass have been established as a tool in microbial ecology and already successfully used in a variety of surface ecosystems. In the Eastern Tropical North Pacific Ocean (ETNP), the oxygen minimum zone (OMZ) presents between 100~800 m depths characterized by dissolved oxygen concentration of less than 20 µM. IPLs were predominant by eukaryotic and bacterial IPLs. Intact polar isoprenoid glycerol dialkyl glycerol tetraethers (IP GDGTs), the biomarker for living Archaea, were detected after purification of the total lipids extract (TLE) using preparative HPLC. Glycolipids which are mainly derived from photosynthetic membranes were dominant in the euphotic zone. With increasing depth, phospholipids and betaine lipids (BL) became dominant components in the OMZ and deep oxycline layers. In the surface layers where light and oxygen could penetrate, photosynthetic organisms, such as photosynthetic algae and cyanobacteria, produced abundant glycolipids. Glycolipids were decreased quickly with increasing depth probably due to remineralization. In the oxygen minimum zone, eukaryotic and bacterial organisms which could survive under oxygen limitation condition accumulated and produced abundant phospholipids and BL. Ratios between phosphorous-containing lipids and their corresponding non-phosphorous-containing substitute lipids, e.g., SQDG/PG and BL/PC (SQDG: sulfoquinovosyldiacylglycerol, PG; phosphatidylglycerol, PC: phosphatidylcholine) were high at depths where phosphate was abundant suggesting that not only phosphate limitation but also the microbial community inhabiting in the oceanic water impact enrichment of substitute lipids. Archaeal IP GDGTs peaked in the upper layers of the OMZ, which exhibited different from peaks of most glycerol ether core lipids (glycerol ether lipids without head groups representing fossil signal) in the deeper depths of the OMZ indicating that IP GDGTs represented an in-situ contribution from the planktonic archaeal community whereas core lipids were exported downward and accumulated in the mid OMZ with a longer residence time. After exported to the sediment, IPLs derived from the upper water column would either rapidly degrade or bury as fossil components. Degradation kinetics of IPLs could influence the interpretation of abundant observed archaeal IPLs in the deep biosphere. Based on a radiotracer experiment and a new comprehensive modeling work, half-life of model archaeal IPL increased with depth from 20 to 310 kyrs, which was relatively longer than the microbial community turnover times of 1.6 to 73 kyrs. It is suggested that a substantial fraction of the archaeal IPLs in marine sediments were fossil components of past microbial populations. Based on the observed IPL concentration and their degradation kinetics, the in-situ synthesis rates of archaeal IPL fell into a range of 1000 pg ml-1 yr-1 to 0.2 pg ml-1 yr-1 from surface to 1 km depth. Such a result is equivalent to the annual production of 7× 105 to 140 archaeal cells ml-1 sediment. Due to the high fossil proportion of archaeal IPLs of probably more than 80%, previously estimated subseafloor living biomass were probably too high. Therefore, the abundant archaeal IPL in subsurface sediments may not reflect a dominant archaeal community of deep biosphere. Ethane and propane as metabolic products of microorganisms are widely detected in the anoxic cold marine sediments. Through a test of several C-2 and C-3 compounds for their alkane-producing potential in anoxic Wadden Sea sediment, alkane production could be observed from ethylene, ethanethiol and propanethiol. Among these three substrates, ethylene had the maximum conversion efficiency for alkane production. Compared to the incubation with sterilized sediment, methanogens were involved in the alkane production. The initial H2 concentration required to stimulate ethanogenesis from ethylene was lower than 0.01% H2. After 80-days of incubation, an ethane-producing enrichment with ethylene as the substrate was used for molecular characterization. Methanocalculus and sequences belonging to the Methanomicrobiales were the dominant groups in the archaeal 16S rRNA gene library and the mcrA gene library, respectively. Methanocalculus is a candidate responsible for ethanogenesis from ethylene.
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