Distributions of phospholipid and glycolipid fatty acids in two strains of different functional Erythrobacter sp. isolated from South China Sea

The comparison of the fatty acids between aerobic anoxygenic phototrophic bacteria (AAPB) and their phylogenetic relatives has been a fascinating but yet enigmatic topic, enhancing our understanding of physiological variations between these evolutionarily related microorganisms. Two strains of marine bacteria, both phylogenetically falling into Erythrobacter sp., were isolated from the South China Sea, and demonstrated, respectively, to be an aerobic anoxygenic phototrophic bacteria (AAPB) (JL475) which is capable of anoxygenic photosynthesis via BChl a, and an obligate heterotroph (JL316) with a lack of BChl a, on the basis of phylogenetic analysis and pure culture cultivation. Phospholipid fatty acids (PLFA) and glycolipid fatty acids (GLFA) of the two strains were extracted and analyzed by gas chromatographymass spectrometry. The PLFA in JL475 AAPB are characterized by C_18:1 C_18:2ω7,13 and C_18:1, with the C_18:2ω7,13 being a specific compound for AAPB and in particular for Erythrobacter longus and some of its phylogenetically closely related relatives. The JL316 strain is characterized in PLFA by the presence of C_18:1, C_16:1 and C_16:0, and in particular C_17:1. GLFA do not show any discrimination between the two strains. Four α,ω-dicarboxylic acids, including 1,8-octanedioic acid, 1,9-nonanedioic acid, 1,10-decanedioic acid and 1,11-undecanedioic acid, are present only in JL316 GLFA, presumably derived from metabolic products. C₁₄-C₁₆ 2-hydroxy fatty acids were found in the two strains, probably assuming a similar function of their LPS in outer membranes.     

Organic matter from a sediment trap experiment in the equatorial north Atlantic: wax esters,steryl esters,triacylglycerols and alkyldiacylglycerols

The vertical flux and composition of wax esters, steryl esters, triacylglycerols, and alkyldiacylglycerols in particulate matter was determined in the equatorial Atlantic Ocean by deploying sediment traps at 389, 988, 3,755 and 5,068 m. Detailed compositional analyses of these lipids were carried out by high temperature glass capillary gas chromatography and gas chromatography/mass spectrometry.The distributions of these lipids are discussed in terms of potential biological sources. Zooplankton fecal matter and intact zooplankters may represent the most important input of these compounds to the shallower two traps, while the material in the deeper two traps appears to have been biogeochemically altered. The finding of these biochemically important compounds, often unsaturated, indicates that particle transit through the water column must be relatively fast.Wax esters were most abundant in the 389 m sediment trap and decreased with increasing trap depth. Compounds ranging from C₂₈–C₄₄ were present at all depths. The major homologs were C₃₂, C₃₄ and C₃₆, most often monounsaturated. The dominant alcohol/acid combinations in the 389 m trap were $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{14:0}}$ and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{16:0}}$, but in the 988 m sample, $\text{C}{}_{\mathrm{16:0}}\text{C}{}_{\mathrm{18:1}}$ was the major wax ester. A flux maximum was observed for steryl esters at 988 m. Cholesteryl esters of C_14:0, C_16:1 and C_16:0, and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{18:0}}$ fatty acids were the dominant steryl esters. For triacylglycerols, fluxes in the 389 and 988 m traps were similar, while the deeper pair of traps contained much less triacylglycerol. C₄₆, C₄₈, C₅₀ and C₅₂ compounds were the major triacylglycerols. Constituent fatty acids in the 389 m and 988 m samples were mainly C_14:0, C_16:1, C_16:0, C_18:1 and C_18:0. In the 988 m material, C_20:5 and C_22:6 were also dominant. A homologous series of alkyldiacylglycerols was abundant in the 389 m trap material. The alkyldiacylglycerols consisted of C₄₆–C₅₆ compounds composed of C_16:0 alkyl moieties and C_14:0, C_16:0, C_18:1, and C_18:0 fatty acids.     

Hydrogen isotopic fractionation in lipid biosynthesis by H2-consuming Desulfobacterium autotrophicum

We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (−37‰ ? δD ? 993‰). H₂ of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H₂, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H₂, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H₂/CO₂ are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H₂ as a significant source of fatty acid hydrogen. Grown on either H₂/CO₂ or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 ? α_FA-water ? 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that α_FA-water generally increases with length of the carbon chain from C₁₄ to C₁₇ among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H₂-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.     

The lipid chemistry of an interfacial sediment from the Peru Continental Shelf: Fatty acids,alcohols, aliphatic ketones and hydrocarbons

A sample of the sediment-water column interface which lies on the continental shelf under the Peru upwelling regime, has been examined for fatty acids, fatty alcohols, ketones and hydrocarbons. Fatty acids were the most abundant compound class, ranging from C₁₂-C₂₄, with 16:0 as the major component (765.5 μg/g dry sediment). The alcohols were dominated by 3,7,11,15-tetramethylhexadeca-2-en-ol (phytol), with even-chain n-alcohols in the range C₁₄-C₂₀. The ketones consisted of C₃₇-C₃₉ di- and tri-unsaturated alken-2-ones and alken-3-ones. Both alkanes and alkenes were present in the hydrocarbon fraction; the alkanes ranging from C₁₃ — C₂₀ and comprising both straight chain and isoprenoid compounds; the alkenes consisting of isomeric pairs of C₂₅ branched trienes and tetraenes. The data indicate that the organic content has been contributed very largely from marine sources (probably mainly from phytoplankton and bacteria), showing little terrigenous influence. The presence of labile compounds such as polyunsaturated fatty acids (with two to six double bonds), implies that the sediment has undergone very little diagenetic alteration, and the lipids are probably largely unchanged from the state in which they actually reached the sediment. They may therefore serve as a useful baseline in assessing diagenesis in older sediments, where diagenetic transformations are more advanced.     

Long-chain carboxylic acids in pyrolysates of Green River kerogen

Long-chain fatty acids (C₁₀-C₃₂), as well as C₁₄-C21 isoprenoid acids (except for C₁₈), have been identified in anhydrous and hydrous pyrolyses products of Green River kerogen (200–400°C, 2–1000 hr). These kerogen-released fatty acids are characterized by a strong even/odd predominance (CPI: 4.8-10.2) with a maximum at C₁₆ followed by lesser amounts of C₁₈ and C₂₂ acids. This distribution is different from that of unbound and bound geolipids extracted from Green River shale. The unbound fatty acids show a weak even/odd predominance (CPI: 1.64) with a maximum at C₁₄, and bound fatty acids display an even/odd predominance (CPI: 2.8) with maxima at C₁₈ and C₃₀. These results suggest that fatty acids were incorporated into kerogen during sedimentation and early diagenesis and were protected from microbial and chemical changes over geological periods of time. Total quantities of fatty acids produced during heating of the kerogen ranged from 0.71 to 3.2 mg/g kerogen. Highest concentrations were obtained when kerogen was heated with water for 100 hr at 300°C. Generally, their amounts did not decrease under hydrous conditions with increase in temperature or heating time, suggesting that significant decarboxylation did not occur under the pyrolysis conditions used, although hydrocarbons were extensively generated.     

Long chain glycolipids with pentose head groups as biomarkers for marine endosymbiotic heterocystous cyanobacteria

Marine endosymbiotic heterocystous cyanobacteria make unique heterocyst glycolipids (HGs) containing pentose (C₅) moieties. Functionally similar HGs with hexose (C₆) moieties found in free-living cyanobacteria occur in the sedimentary record, but C₅ HGs have not been documented in the natural environment. Here we developed a high performance liquid chromatography multiple reaction monitoring (MRM) mass spectrometry (HPLC–MS²) method specific for trace analysis of long chain C₅ HGs and applied it to cultures of Rhizosolenia clevei Ostenfeld and its symbiont Richelia intracellularis which were found to contain C₅ HGs and no C₆ HGs. The method was then applied to suspended particulate matter (SPM) and surface sediment from the Amazon plume region known to harbor marine diatoms carrying heterocystous cyanobacteria as endosymbionts. C₅ HGs were detected in both marine SPM and surface sediments, but not in SPM or surface sediment from freshwater settings in the Amazon basin. Rather, the latter contained C₆ HGs, established biomarkers for free-living heterocystous cyanobacteria. Our results indicate that the C₅ HGs may be potential biomarkers for marine endosymbiotic heterocystous cyanobacteria.     

Bacterial wax esters in recent fluvial sediments

We investigated the molecular inventory of River Danube sediments and identified wax esters with 28–36 carbons, with C₃₀, C₃₁ and C₃₂ homologs the most abundant. They consist of various combinations of n-, iso- and anteiso-aliphatic acid and alcohol moieties, with different isomer distributions for the esters with odd and even carbon numbers. The short chain length (C₂₈–C₃₆), high proportion of methyl moieties and presence of monounsaturated esters together suggest a bacterial origin for the wax esters. The concentration in surface sediments varied from 0 to 741 μg/kg, being significantly enriched at locations with high nutrient concentration and high primary productivity. Cluster analysis of denaturing gradient gel electrophoresis (DGGE) band patterns revealed different bacterial communities in surface sediments from the stream and surface sediments from the reservoir. The concentration in a 70 cm core of rapidly deposited sediments decreased significantly with depth, following first order kinetics, suggesting a loss of the esters within ca. 3 years following burial and hence a low probability for preservation in the geological record. Wax esters in rivers have rarely been investigated; our results suggest that they represent a bacterial response to enhanced primary production, triggered by higher nutrient supply.     

Isoprenoids in a Costa Rican seep oil

The isoprenoid alkanes present in a seep oil from Costa Rica have been examined using gas chromatography and mass spectrometry. In addition to the predominance of the C₁₆ and C₁₈-C₂₀ regular isoprenoid alkanes, the C₂₁ and C₂₃-C₂₅ regular isoprenoid alkanes were identified. The C₂₆, C₂₈ and C₃₀ regular isoprenoid alkanes were tentatively identified. No evidence for the regular C₁₇, C₂₂ or C₂₇ isoprenoid alkanes was found. The compounds 3,7,11- trimethyltetradecane and 3,7,11-trimethylhexadecane were tentatively identified. It is suggested that a higher regular isoprenoid structure (or structures) is required in addition to phytol to account for the distribution of isoprenoid alkanes.     

Early diagenesis of fatty acids in lacustrine sediments—I. Identification and distribution of fatty acids in recent sediment from a freshwater lake

Fatty acids have been isolated and quantitatively determined from a 1.5 m sediment core of Lake Suwa, a eutrophic lake in the central districts of Japan.The fatty acids identified by combined gas chromatography-mass spectrometry were straight-chain saturated (C₁₂ to C₃₄), monounsaturated with even carbon number (C₁₆ to C₂₄) and branched-chain (iso, anteiso, 10-methyloctadecanoic) acids. The concentrations of the higher molecular weight (? C₂₀) saturated fatty acids remained nearly constant throughout the core, suggesting a high degree of preservation of those acids, whereas the monounsaturated and the lower molecular weight saturated fatty acids indicated a great decrease in concentration with depth to an approximately 20cm level. It is suggested that the microbial activity in sediments causes a significant reconstruction of the fatty acid distribution during early diagenesis.     

Insights into preservation of fossil plant cuticles using thermally assisted hydrolysis methylation

The chemical composition of Cretaceous leaf remains showing exceptionally well preserved cuticles was investigated using pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) and thermally assisted hydrolysis methylation (THM)-GC–MS. Samples of Coniferales (Frenelopsis) and Ginkgoales (Nehvizdya penalveri) leaf remains were collected from freshwater and coastal marine depositional environments. Material for pyrolysis included (i) untreated leaves and cuticles obtained after extraction from mineral rock matrix and bleaching, (ii) kerogen fraction from both materials, (iii) non-hydrolysable fraction from kerogen. The THM-GC–MS data from untreated leaves and bleached cuticles show that the fossil cuticle geopolymer essentially released aliphatic components upon thermal treatment, with a dominance of fatty acids (FAs) and n-alkanes/n-alkenes. The FAs are essentially resistant to bleaching and remain after solvent extraction. They occur mainly as short chain compounds ranging from C₆ to C₁₆ and with maximum abundance at C₈–C₉. The n-alkanes/n-alkenes from kerogen and the non-hydrolysable residue occur mainly as short chain compounds in the range C₁₀–C₁₆, with the highest abundance at C₉–C₁₂. The THM-GC–MS pyrograms of the fossil cuticles differ from those of cutan from fresh living plants. They support the preservation model via polymerization of monomers derived from cutin or from unsaturated cell FAs.     

Conversion of sedimentary fatty acids from extractable (unbound + bound) to tightly bound form during mild heating

Prolonged heating (1–248 days) of a recent sediment was conducted under mild conditions (65 and 83°C) to understand the thermal behavior of extractable (unbound and bound) fatty acids (C_12C32). In the course of the heating, the concentrations of saturated and monounsaturated fatty acids first decreased, and then increased. This indicates that extractable fatty acids can be converted to a tightly bound form upon heating, before fatty acids are extensively released from sediment matrices. Changes in molecular distributions of extractable fatty acids upon heating were also observed. The higher molecular weight fatty acids (?C₂₀) are more likely to become tightly bound than are lower molecular weight (<C₂₀). Monounsaturated fatty acids (C_16:1 and C_18:1) are more easily converted to the tightly bound form than polyunsaturated fatty acids (C_18:2 and C_18:3). These differences probably reflect their mode of occurrence in sediments, which are closely related to their origin.     

Bitumen from Coalport tar tunnel

The Coalport (Shropshire, U.K.) Tar Tunnel bitumen has been known since 1787 and the first geochemical data are reported here. The bitumen was analyzed for molecular markers useful for correlational studies. Gas chromatographic analysis of aliphatic and aromatic hydrocarbons failed to detect any specific major components normally used for genetic correlational and maturational studies. A search for minor and trace components by gas chromatographic-mass fragmentographic analysis showed the presence of triterpenoid hydrocarbons primarily of the 17α (H)-hopane series (C₂₇ to C₃₅, ex. C₂₈) and a C₂₆ to C₃₁ series of ring A/B demethylated hopanes. Two homologous sterane series (C₂₇ to C₂₉) of the 5α, 14β, 17β (H)-sterane and 13β, 17α (H)-diasterane type were also detected. Pophyrins of the DPEP and etio series (C₂₇ to C₄₁, DPEP/etio > 1) were also found. Characterization of their alkyl substitution pattern demonstrated C₁, C₂ and C₃ substituents on the pyrole moieties of the parent petroporphyrins.The molecular markers detected in this bitumen indicate its biogenic origin and show evidence of diagenetic and geothermal maturation processes. The overall geochemical characteristics of the Coalport Tar Tunnel bitumen suggest that it corresponds to a well matured crude oil, which was heavily altered by in-reservoir biodegradation or close to surface exposure.     

Lipid geochemistry in a sediment core from Ruoergai Marsh deposit (Eastern Qinghai-Tibet plateau, China)

Peats in a sediment core from Ruoergai bog, which has a cold and moist plateau climate with major source input from herbaceous plants, have been studied by GC–MS in order to understand the composition and diagenetic processes of lipids in this depositional environment. Long chain components (C₂₁–C₃₅) predominate in the n-alkanes, n-alk-1-enes, n-fatty acids, n-alkan-2-ones and n-alkanols with a maximum of C₃₁, C_27, C₂₂ or C_24, C₂₃ or C₂₅ and C₂₂, respectively. A herbaceous origin for these long chain compounds is suggested, and this is supported by their stable carbon isotopic compositions. Diterpenoid hydrocarbons with abietane, pimarane and kaurane skeletons, some of which have not been reported often in modern sediments, are prominent and are derived from higher plants. Several triterpenoid ketones and alcohols with oleanane or lupane skeletons, and a series of des-A-triterpenoid hydrocarbons which have not been reported often in modern sediments are also present, and are assigned to a higher plant source. Hopanoids, including their alkanes, alkenes, ketones, alcohols and esters, are abundant and of bacterial origin. Steroid ketones and alkanols are dominated by C₂₉ homologues. C₂₈ and C₂₉ steroids are derived mainly from higher plants, whereas the C₂₇ component is assigned to a microbial source. The presence of short-chain n-alkanes with no odd-even carbon predominance, bacterially derived fatty acids (C₁₄, C₁₅, iso- and unsaturated acids), n-alkan-2-ones, des-A-triterpenoid hydrocarbons, hopanoids and some steroid ketones indicate that intense microbial reworking of the organic matter has taken place in this depositional environment. The chemical and biochemical conversions of some cyclic alkenes to alkanes, such as tricyclic diterpenoids, tetracyclic terpenoids and steroid ketones, are also evident with depth. The dominance of C₂₀ components in the diterpenoid hydrocarbons may reflect an oxidizing or reducing depositional condition.     

Isotopic fractionation associated with biosynthesis of fatty acids by a marine bacterium under oxic and anoxic conditions

Shewanella putrefaciens (Strain MR-4), a gram negative facultative marine bacterium, was grown to stationary phase under both aerobic and anaerobic conditions using lactate as the sole carbon source. Aerobically-produced cells were slightly enriched in ¹³C (+1.5‰) relative to the lactate carbon source, whereas those from anaerobic growth were depleted in ¹³C (−2.2‰). The distribution of fatty acids produced under aerobic conditions was similar to that resulting from anaerobic growth, being dominated by C_16:1 ω7 and C_16:0 fatty acids with a lesser amount of the C_18:1 ω7 component. Low concentrations of saturated even numbered normal fatty acids in the C₁₄ to C₁₈ range, and iso-C_15:0 were synthesized under both conditions. Fatty acids from anaerobic cultures (average δ¹³C=−37.8‰) were considerably depleted in ¹³C relative to their aerobically-synthesized counterparts (−28.8‰). The distinct differences in isotopic composition of both whole cells and individual fatty acid components result from differences in assimilation pathways. Under aerobic conditions, the primary route of assimilation involves the pyruvate dehydrogenase enzyme complex which produces acetyl-CoA, the precursor to lipid synthesis. In contrast, under anaerobic conditions formate, and not acetate, is the central intermediate in carbon assimilation with the precursors to fatty acid synthesis being produced via the serine pathway. Anaerobically-produced bacterial fatty acids were depleted by up to 12‰ relative to the carbon source. Therefore, detection of isotopically depleted fatty acids in sediments may be falsely attributed to a terrestrial origin, when in fact they are the result of bacterial resynthesis.     

HPLC separation of higher fullerenes in the synthetical “graphite smokes” soot

Higher fullerenes(C84,C90,C92,C94 and C96) were successfully isolated from the Soxhlet extract of the synthetical "Graphote Smokes" soot(GS sample) by using a big Cosmosil Buckysep(Phenomenex) column(250 mm × 10 mm) with a large injection.The fractions isolated have been determined by high performance liquid chro-matography(HPLC) and laser desorption mass spectrometry(LDMS).It is found that there are different fullerenes molecules in different fractions with retention time.The result indicates that fullerenes do exist in GS samples.Also,it excludes the suspicion to some extent that fullerene molecules might be generated by the laser desorption process in the LDMS.In addition,it also provides the experimental basis for the study of natural higher fullerenes and might be helpful to figure out the question if higher fullerenes do exist in the natural samples.     

Laboratory sulfurisation of the marine microalga Nannochloropsis salina

To understand more fully the mode of preservation of organic matter in marine sediments, laboratory sulfurisation of intact cells of the cultured microalga Nannochloropsis salina was performed using inorganic polysulfides in seawater at 50°C. Solvent extractable and non-extractable materials were analysed by GC–MS and Py–GC–MS, respectively, to study the incorporation of sulfur into the microalgal organic matter. No GC-amenable sulfur-containing compounds were found in the extracts apart from some minor thiophenes with a phytanyl carbon skeleton. The residue after extraction and hydrolysis contained abundant macromolecular sulfur-containing moieties as revealed by the presence of dominant C₂₈–C₃₂ thiols, thiophenes, thianes and thiolanes in the flash pyrolysates. These products are thought to be formed from moieties derived from sulfurisation of C₂₈–C₃₂ diols and alkenols, characteristic lipids of N. salina. C₁–C₂ alkylated thiophenes were also found in the pyrolysates and probably result from moieties formed upon sulfurisation of carbohydrates. The highly resistant biomacromolecule (algaenan) synthesised by N. salina remains unaffected by sulfurisation. The non-hydrolysable residue isolated from the sulfurised N. salina thus comprises algaenan and (poly)sulfide-bound long alkyl chains. The sulfurisation experiments show that both selective preservation of algaenans and lipid and carbohydrate “vulcanisation” can be involved in the preservation of algal organic matter in marine environments.     

The petroporphyrins of a Cretaceous oil

The petroporphyrins of a Cretaceous crude oil, La Paz, from western Venezuela are shown to be a mixture of etio and DPEP homologues (C₂₇-C₃₉) maximising at C₃₀ and C₃₁, respectively. Minor amounts of rhodoporphyrins (C₃₀-C₃₉) are also present. Thin-layer chromatography afforded fractions which have been shown by mass spectrometry to contain up to 80% of a single-molecular-weight species. Oxidative degradation of La Paz petroporphyrins to maleimides and mass-spectrometric study of t.l.c. fractions indicate that some of these porphyrins are to a great extent incompletely substituted. Dealkylation reactions have presumably played an important role in their geologic history. Furthermore, the relative simplicity of the alkyl substitution pattern of the La Paz petroporphyrins suggests that transalkylation reactions have not taken place to any significant extent.The fraction of petroporphyrins isolated from the asphaltenes contains a higher proportion of the DPEP homologues than do the total petroporphyrins isolated from the original crude oil.     

Recent vegetation history from a swampy environment to a pond based on macromolecular organic matter (lignin and fatty acids) and pollen sedimentary records

Evidence of environmental and vegetation changes in the catchment area of a small pond created artificially during the Middle Ages from a swampy area was provided by coupling palynology data and a detailed study of macromolecular organic matter (OM). Tetramethylammonium hydroxide (TMAH) thermochemolysis after solvent extraction was used to characterize macromolecular OM and particularly lignin and fatty acids (FAs). Molecular ratios such as TAR_(FA), C_16:1/C_16:0 and C_18:1/C_18:0 were calculated to characterize the FAs incorporated into the macromolecular OM. Moreover, syringyl vs. vanillyl phenols (S/V) and cinnamyl vs. vanillyl phenols (C/V) molecular ratios were investigated to fingerprint the lignin sources. These different markers suggested that the swampy area was dominated by a non-woody angiosperm input and gave rise to pond status over a period of several centuries. Indeed, TAR_(FA) correlated with the aquatic contribution, which became predominant after creation of the pond. The use of ratios of total acid phenols to the total aldehyde phenols of syringyl or vanillyl units (Ad/Al_(s), Ad/Al_(v)), which are related to the degree of oxidation of lignin, revealed the irregular operation of oxidative conditions.     

Organic geochemistry of the Dongsheng sedimentary uranium ore deposits,China

Organic matter (OM) associated with the Dongsheng sedimentary U ore hosting sandstone/siltstone was characterized by Rock-Eval, gas chromatography–mass spectrometry and stable C isotope analysis and compared to other OM in the sandstone/siltstone interbedded organic matter-rich strata. The OM in all of the analyzed samples is Type III with Ro less than 0.6%, indicating that the OM associated with these U ore deposits can be classified as a poor hydrocarbon source potential for oil and gas. n-Alkanes in the organic-rich strata are characterized by a higher relative abundance of high-molecular-weight (HMW) homologues and are dominated by C₂₅, C₂₇ or C₂₉ with distinct odd-to-even C number predominances from C₂₃ to C₂₉. In contrast, in the sandstone/siltstone samples, the n-alkanes have a higher relative abundance of medium-molecular-weight homologues and are dominated by C₂₂ with no or only slight odd-to-even C number predominances from C₂₃ to C₂₉. Methyl alkanoates in the sandstone/siltstone extracts range from C₁₄ to C₃₀, maximizing at C₁₆, with a strong even C number predominance, but in the organic-rich layers the HMW homologues are higher, maximizing at C₂₄, C₂₆ or C₂₈, also with an even predominance above C₂₂. n-Alkanes in the sandstone/siltstone sequence are significantly depleted in ¹³C relative to n-alkanes in most of the organic-rich strata. Diasterenes, ββ-hopanes and hopenes are present in nearly all the organic-rich sediments but in the sandstone/siltstone samples they occur as the geologically mature isomers. All the results indicate that the OM in the Dongsheng U ore body is derived from different kinds of source materials. The organic compounds in the organic-rich strata are mainly terrestrial, whereas, in the sand/siltstones, they are derived mainly from aquatic biota. Similar distribution patterns and consistent δ¹³C variations between n-alkanes and methyl alkanoates in corresponding samples suggest they are derived from the same precursors. The OM in the organic-rich strata does not appear to have a direct role in the precipitation of the U ore in the sandstone, but an indirect role cannot be excluded. The OM in the U hosting sandstone shows a relatively low hydrogen index, presumably due to oxidation or radiolytic damage.