Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments

Li, Chao; Sessions, Alex L.; Kinnaman, Franklin S.; Valentine, David L.

doi:10.1016/j.gca.2009.05.056

Cited by 81 publications

(72 citation statements)

References 76 publications

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“…Isoprenoid lipids are typically D depleted relative to n-alkyl lipids by 100‰ or more, a pattern now widely confirmed in both culture (13,16,19) and environmental samples (12,18). However, significant variability within single classes of lipids (e.g., fatty acids) cannot be explained because the chemical mechanisms of lipid biosynthesis are strongly conserved across most bacterial and eukaryotic phyla (22-25).…”

mentioning

confidence: 99%

“…Jones et al (17) measured fatty acids extracted from coastal marine particulate organic matter (POM) and found ␦D values ranging from Ϫ73 to Ϫ237‰. Measurements of lipids from marine sediments have extended this range from Ϫ32 to Ϫ348‰ for lipids with n-alkyl skeletons and Ϫ148 to Ϫ469‰ for those with isoprenoid skeletons (18). Because the lipids measured by both studies likely derive from marine organisms inhabiting seawater of essentially constant ␦D value (Ϸ0‰), such differences cannot be due to varying environmental water.…”

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confidence: 99%

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Large D/H variations in bacterial lipids reflect central metabolic pathways

Zhang¹,

Gillespie

Sessions

2009

Proc. Natl. Acad. Sci. U.S.A.

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Large hydrogen-isotopic (D/H) fractionations between lipids and growth water have been observed in most organisms studied to date. These fractionations are generally attributed to isotope effects in the biosynthesis of lipids, and are frequently assumed to be approximately constant for the purpose of reconstructing climatic variables. Here, we report D/H fractionations between lipids and water in 4 cultured members of the phylum Proteobacteria, and show that they can vary by up to 500‰ in a single organism. The variation cannot be attributed to lipid biosynthesis as there is no significant change in these pathways between cultures, nor can it be attributed to changing substrate D/H ratios. More importantly, lipid/water D/H fractionations vary systematically with metabolism: chemoautotrophic growth (approximately ؊200 to ؊400‰), photoautotrophic growth (؊150 to ؊250‰), heterotrophic growth on sugars (0 to ؊150‰), and heterotrophic growth on TCA-cycle precursors and intermediates (؊50 to ؉200‰) all yield different fractionations. We hypothesize that the D/H ratios of lipids are controlled largely by those of NADPH used for biosynthesis, rather than by isotope effects within the lipid biosynthetic pathway itself. Our results suggest that different central metabolic pathways yield NADPH-and indirectly lipids-with characteristic isotopic compositions. If so, lipid ␦D values could become an important biogeochemical tool for linking lipids to energy metabolism, and would yield information that is highly complementary to that provided by 13 C about pathways of carbon fixation.fatty acids ͉ fractionation ͉ metabolism ͉ hydrogen isotopes T he hydrogen-isotopic composition ( 2 H/ 1 H or D/H ratio, commonly expressed as a ␦D value) of lipids is being explored by scientists with diverse interests, including the origins of natural products (1, 2), biogeochemical cycles (3), petroleum systems (4), and paleoclimate (5-7). Because the D/H ratios of lipids are generally conserved over Ϸ10 6 -year time scales (8), they are a potentially useful tracer of biogeochemical pathways and processes in the environment. Most research to date has focused on higher plants, in which environmental water is the sole source of external hydrogen and consequently provides primary control over the D/H ratio of biosynthesized lipids (9). Although ␦D values for plant lipids and environmental water are generally well correlated, they are also substantially offset from each other. The biochemical basis for this lipid/water fractionation is not well understood. It is generally assumed to arise from a combination of isotope effects during photosynthesis and the biosynthesis of lipids (9-12), and is often treated as approximately constant to reconstruct isotopic compositions of environmental water as a paleoclimate proxy.There is, however, mounting evidence that the net D/H fractionation between lipids and water can vary by up to 150‰ in plants, even in the same organism (12-16). Modest fractionations associated with fatty acid elongation and desaturation ...

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confidence: 99%

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confidence: 99%

Large D/H variations in bacterial lipids reflect central metabolic pathways

Zhang¹,

Gillespie

Sessions

2009

Proc. Natl. Acad. Sci. U.S.A.

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202

268

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“…At left are the fatty acids from the cultivation studies of Zhang et al, distinguished by substrates that feed into the identified metabolic pathways. At right is a histogram summarizing the distribution of deuterium content for Ϸ1,000 analytes extracted from the anoxic marine sediments of the Santa Barbara Basin (11). Included in the histogram are several classes of compounds, including fatty acids, alcohols, alkanes, and isoprenoids, the latter of which tend to be depleted in deuterium.…”

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confidence: 99%

Isotopic remembrance of metabolism past

Valentine

2009

Proc. Natl. Acad. Sci. U.S.A.

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“…Potential variations of α PA from different contributors are either small or levelled out by integration over ecosystems. A surprising constancy in δD PA has also been observed in a sediment core from the Santa Barbara Basin (Li et al, 2009). There, the δD PA remained constant even in the presence of heterotrophic palmitic acid producers.…”

Section: Palmitic Acid δDmentioning

confidence: 72%

“…This could indicate that the constancy in α PA is not only limited to phototrophic organisms as observed here and by Huang et al (2004), but also extends to heterotrophic organisms. The constancy could be caused by the very similar biosynthetic pathway for palmitic acid in bacteria and eukaryotes (Li et al, 2009).…”

Section: Palmitic Acid δDmentioning

confidence: 99%

Testing the D / H ratio of alkenones and palmitic acid as salinity proxies in the Amazon Plume

Häggi

Chiessi²,

Schefuß

2015

Biogeosciences

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Abstract. The stable hydrogen isotope composition of lipid biomarkers, such as alkenones, is a promising new tool for the improvement of palaeosalinity reconstructions. Laboratory studies confirmed the correlation between lipid biomarker δD composition (δD Lipid ), water δD composition (δD H 2 O ) and salinity; yet there is limited insight into the applicability of this proxy in oceanic environments. To fill this gap, we test the use of the δD composition of alkenones (δD C 37 ) and palmitic acid (δD PA ) as salinity proxies using samples of surface suspended material along the distinct salinity gradient induced by the Amazon Plume. Our results indicate a positive correlation between salinity and δD H 2 O , while the relationship between δD H 2 O and δD Lipid is more complex: δD PA correlates strongly with δD H 2 O (r 2 = 0.81) and shows a salinity-dependent isotopic fractionation factor. δD C 37 only correlates with δD H 2 O in a small number (n = 8) of samples with alkenone concentrations > 10 ng L −1 , while there is no correlation if all samples are taken into account. These findings are mirrored by alkenone-based temperature reconstructions, which are inaccurate for samples with low alkenone concentrations. Deviations in δD C 37 and temperature are likely to be caused by limited haptophyte algae growth due to low salinity and light limitation imposed by the Amazon Plume. Our study confirms the applicability of δD Lipid as a salinity proxy in oceanic environments. But it raises a note of caution concerning regions where low alkenone production can be expected due to low salinity and light limitation, for instance, under strong riverine discharge.

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Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments

Cited by 81 publications

References 76 publications

Large D/H variations in bacterial lipids reflect central metabolic pathways

Large D/H variations in bacterial lipids reflect central metabolic pathways

Isotopic remembrance of metabolism past

Testing the D / H ratio of alkenones and palmitic acid as salinity proxies in the Amazon Plume

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