Degradation of alkenones by aerobic heterotrophic bacteria: Selective or not?

Rontani, Jean‐François; Harji, Ranjita; Guasco, Sophie; Prahl, Fredrick G.; Volkman, John K.; Bhosle, N.B.; Bonin, Patricia

doi:10.1016/j.orggeochem.2007.10.003

Cited by 54 publications

(51 citation statements)

References 56 publications

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“…The amount of 16:3-phytol amounted to 360 nmol g Ϫ1 FW in senescing leaves, suggesting that a predominant fraction of phytyl released from chlorophyll is channeled into fatty acid phytyl ester synthesis. Previously, phytyl esters were found in bacteria, dinoflagellates, chlorophytes, mosses, grasses, pea, and some Amazonian plant species (28,(37)(38)(39)(40)(41). Furthermore, phytyl esters were detected in the chilling sensitive 1 mutant (chs1) of Arabidopsis after exposure to 14°C (17).…”

Section: Discussionmentioning

confidence: 99%

A Salvage Pathway for Phytol Metabolism in Arabidopsis

Ischebeck¹,

Zbierzak

Kanwischer

et al. 2006

Journal of Biological Chemistry

174

204

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Chlorophyll is the most abundant photosynthetic pigment in higher plants. During senescence, chlorophyll is hydrolyzed, resulting in the release of free phytol and chlorophyllide. Although the degradation of chlorophyllide has been studied in depth, the metabolic fate of phytol in plants is less clear. Here, we provide evidence that phytol can be incorporated into chlorophyll, tocopherol, and lipid esters by Arabidopsis seedlings. Phytol is phosphorylated to phytyl-phosphate and phytyl-diphosphate by two successive kinase activities associated with chloroplast envelope membranes of Arabidopsis. Although phytol kinase is CTP-dependent, the second kinase reaction, phytyl-phosphate kinase, shows broader specificity for CTP, GTP, UTP, and ATP. Therefore, in addition to de novo synthesis from geranylgeranyl-diphosphate, phosphorylation of free phytol represents an alternative route for phytyl-diphosphate production as the precursor for chloroplast prenyl lipid synthesis. Lipid esters are produced after feeding phytol to Arabidopsis seedlings, and they also accumulate in large amounts in leaves during senescence. The predominant phytyl ester that accumulates during senescence is hexadecatrienoic acid phytyl ester. Fatty acid phytyl ester synthesis by protein extracts of Arabidopsis is stimulated in the presence of phytol-and acyl-CoA esters. Thus, Arabidopsis contains a distinct enzymatic machinery for redirecting free phytol released from chlorophyll degradation into chloroplast lipid metabolism.Isoprenoids represent one of the most diverse classes of naturally occurring compounds. In plants, photosynthetic pigments (i.e. carotenoids and chlorophyll) are derived from isoprenoid biosynthesis. Furthermore, electron carriers of photosynthesis (plastoquinone, phylloquinone), respiration (ubiquinone), and antioxidants (tocopherol) contain isoprenyl side chains (1). Two pathways for isoprenoid synthesis exist in higher plants, the mevalonate pathway localized to the cytosol and the methylerythritol-phosphate pathway found in plastids (2, 3). Plastid isoprenoid metabolism largely depends on the methylerythritol-phosphate pathway. However, some exchange of isoprenoid units between the plastid and the cytosol seems to occur (4). Geranylgeranyl-diphosphate plays an important role in plastid isoprenoid metabolism, because it is the precursor for the synthesis of carotenoids, tocotrienols, chlorophyll, and phytyl-diphosphate (phytyl-PP).3 The existence of two pathways for chlorophyll synthesis was suggested. The first is the direct transfer of a phytyl group onto chlorophyllide from phytyl-PP at the envelope membrane, and the second is the geranylgeranylation of chlorophyllide at the thylakoid membranes (5). Keller et al. (6) identified an Arabidopsis cDNA encoding geranylgeranyl reductase. This enzyme was proposed to convert geranylgeranyl-diphosphate into phytyl-PP and, in addition, to reduce the geranylgeranylated form of chlorophyll to (phytyl-)chlorophyll. A large fraction of phytyl-PP is channeled into chlorophyll synthe...

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Section: Discussionmentioning

confidence: 99%

A Salvage Pathway for Phytol Metabolism in Arabidopsis

Ischebeck¹,

Zbierzak

Kanwischer

et al. 2006

Journal of Biological Chemistry

174

204

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“…Thus, although alkenone can be used to estimate production for both the calcified and non-calcified life stages, the cellular content cannot be assumed to be the same in the two stages. [16] Culture experiments have shown that some bacteria preferentially degrade tri-and tetra-unsaturated alkenones over di-unsaturated alkenone, resulting in an apparent increase in temperature estimates based on the alkenone unsaturation index [Rontani et al, 2005[Rontani et al, , 2008Zabeti et al, 2010]. If significant preferential degradation of alkenones occurred in the sediments studied here, the relative abundance of C 37:4 alkenone would be expected to decrease with increasing sediment age and U K ′ 37 values would be expected to increase.…”

Section: E Huxleyi Blooms and Alkenone As A Biomarker Of Productionmentioning

confidence: 97%

Enhancement of coccolithophorid blooms in the Bering Sea by recent environmental changes

Harada

Sato

Oguri

et al. 2012

Global Biogeochemical Cycles

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[1] Since 1997, ocean color satellite images have revealed large-scale blooms of the coccolithophorid Emiliania huxleyi in the eastern Bering Sea. The blooms are often sustained over several months and have caused ecosystem changes in the Arctic Ocean, as well as in the Bering Sea. We examined continental shelf sediment profiles of alkenone, a biomarker for E. huxleyi, covering the past $70 years. The alkenone records suggest that large E. huxleyi blooms are a novel feature in the Bering Sea as they have occurred only since the late 1970s. Recent changes in alkenone content were closely related to the 1976-77 climatic regime shift in the North Pacific, implying that warming and freshening of Bering Sea waters promoted E. huxleyi blooms. The production rate of diatoms (total valves in sediment samples), the dominant primary producers in the Bering Sea, also increased during the past several decades. However, the ratio of alkenone content to total diatom valves in the sediments increased as E. huxleyi production increased, suggesting that the increase in the E. huxleyi production rate frequently exceeded the increase in the diatom production rate. Overall, our results indicate a possible subarctic region ecosystem shift driven by climate change.

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“…Selective bacterial degradation of alkenones can occur and the bacterial metabolic pathway includes isotopic fractionation during the degradation of alkenones to alkenols (Gong and Hollander, 1999;Rontani et al, 2005;Rontani et al, 2008;Sun et al, 2004). However, if bacterial activity occurred, it is not expected to influence the radiocarbon content of the alkenones, since radiocarbon data reported according to Stuiver and Polach (1977) are corrected for isotopic fractionation during sample formation, decay as well as processing.…”

Section: Degradation Of Alkenones During Storagementioning

confidence: 99%

Timescales of lateral sediment transport in the Panama Basin as revealed by radiocarbon ages of alkenones, total organic carbon and foraminifera

Kusch

Eglinton

Mix

et al. 2010

Earth and Planetary Science Letters

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Paired radiocarbon measurements on haptophyte biomarkers (alkenones) and on cooccurring tests of planktic foraminifera (Neogloboquadrina dutertrei and Globogerinoides sacculifer) from late glacial to Holocene sediments at core locations ME0005-24JC, Y69-71P, and MC16 from the south-western and central Panama Basin indicate no significant addition of pre-aged alkenones by lateral advection. The strong temporal correspondence between alkenones, foraminifera and total organic carbon (TOC) also implies negligible contributions of aged terrigenous material. Considering controversial evidence for sediment redistribution in previous studies of these sites, our data imply that the laterally supplied material cannot stem from remobilization of substantially aged sediments.

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Degradation of alkenones by aerobic heterotrophic bacteria: Selective or not?

Cited by 54 publications

References 56 publications

A Salvage Pathway for Phytol Metabolism in Arabidopsis

A Salvage Pathway for Phytol Metabolism in Arabidopsis

Enhancement of coccolithophorid blooms in the Bering Sea by recent environmental changes

Timescales of lateral sediment transport in the Panama Basin as revealed by radiocarbon ages of alkenones, total organic carbon and foraminifera

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