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Lipid biomarkers in ooids from different locations and ages: evidence for a common bacterial flora

Summons, R. E. and Bird, L. R. and Gillespie, A. L. and Pruss, S. B. and Roberts, M. and Sessions, A. L. (2013) Lipid biomarkers in ooids from different locations and ages: evidence for a common bacterial flora. Geobiology, 11 (5). pp. 420-436. ISSN 1472-4677.

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Ooids are one of the common constituents of ancient carbonate rocks, yet the role that microbial communities may or may not play in their formation remains unresolved. To search for evidence of microbial activity in modern and Holocene ooids, samples collected from intertidal waters, beaches and outcrops in the Bahamas and in Shark Bay in Western Australia were examined for their contents of lipid biomarkers. Modern samples from Cat and Andros islands in the Bahamas and from Carbla Beach in Hamelin Pool, Western Australia, showed abundant and notably similar distributions of hydrocarbons, fatty acids (FAs) and alcohols. A large fraction of these lipids were bound into the carbonate matrix and only released on acid dissolution, which suggests that these lipids were being incorporated continuously during ooid growth. The distributions of hydrocarbons, and their disparate carbon isotopic signatures, were consistent with mixed input from cyanobacteria together with small and variable amounts of vascular plant leaf wax [C_(27)–C_(35); δ^(13)C −25 to −32‰Vienna Pee Dee Belemnite (VPDB)]. The FAs comprised a complex mixture of C_(12)–C_(18) normal and branched short-chain compounds with the predominant straight-chain components attributable to bacteria and/or cyanobacteria. Branched FA, especially 10-MeC_(16) and 10-MeC_(17), together with the prevalence of elemental sulfur in the extracts, indicate an origin from sulfate-reducing bacteria. The iso- and anteiso-FA were quite variable in their ^(13)C contents suggesting that they come from organisms with diverse physiologies. Hydrogen isotopic compositions provide further insight into this issue. FAs in each sample show disparate δD values consistent with inputs from autotrophs and heterotrophs. The most enigmatic lipid assemblage is an homologous series of long-chain (C_(24)–C_(32)) FA with pronounced even carbon number preference. Typically, such long-chain FA are thought to come from land plant leaf wax, but in this case, their ^(13)C-enriched isotopic signatures compared to co-occurring n-alkanes (e.g., Hamelin Pool TLE FA C_(24)–C_(32); δ^(13)C −20 to −24.2‰ VPDB; TLE n-alkanes δ^(13)C −24.1 to −26.2 −‰VPDB) indicate a microbial origin, possibly sulfate-reducing bacteria. Lastly, we identified homohopanoic acid and bishomohopanol as the primary degradation products of bacterial hopanoids. The distributions of lipids isolated from Holocene oolites from the Rice Bay Formation of Cat Island, Bahamas were very similar to the beach ooids described above and, in total, these modern and fossil biomarker data lead us to hypothesize that ooids are colonized by a defined microbial community and that these microbes possibly mediate calcification.

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URLURL TypeDescription DOIArticle
Summons, R. E.0000-0002-7144-8537
Bird, L. R.0000-0002-6034-9533
Sessions, A. L.0000-0001-6120-2763
Additional Information:© 2013 John Wiley & Sons Ltd. Received 5 January 2013; accepted 24 May 2013. Article first published online: 21 Jun. 2013. We thank Sara Lincoln and Carolyn Colonero for advice and assistance in the laboratory. David Fike generously provided the ooids from Joulter’s Cays. Work at MIT was supported by grants from the NASA Astrobiology Institute (NNA08CN84A), the NSF Program on Emerging Trends in Biogeochemical Cycles (OCE-0849940) and the NSF Chemical Oceanography Program (OCE-0926372). Funding for sample collection from Cat Island, The Bahamas, was made possible by a Smith College Committee on Faculty Development grant (to SBP). The authors thank two anonymous reviewers for their critical comments on the initial submission.
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Issue or Number:5
Record Number:CaltechAUTHORS:20130909-081720156
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Official Citation:Summons, R. E., Bird, L. R., Gillespie, A. L., Pruss, S. B., Roberts, M. and Sessions, A. L. (2013), Lipid biomarkers in ooids from different locations and ages: evidence for a common bacterial flora. Geobiology, 11: 420–436. doi: 10.1111/gbi.12047
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41158
Deposited By: Tony Diaz
Deposited On:16 Sep 2013 21:30
Last Modified:09 Mar 2020 13:19

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