Table of Contents

• Dataset Description
  • Methods & Sampling
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset contains GenBank and GenBank Short Read Archive (SRA) sequence accession numbers for samples from microbialite mats at Hamelin Pool, Australia and Highborne Cay, Bahamas.

References:
Bernhard et al. 2013. Insights into foraminiferal influences on microfabrics of microbialites at Highborne Cay, Bahamas. PNAS 110(24); published ahead of print May 28, 2013. doi: 10.1073/pnas.1221721110.
Edgcomb et al. 2013. Active eukaryotes in microbialites from Highborne Cay, Bahamas and Hamelin Pool (Shark Bay), Australia. In press, ISME Journal.
Edgcomb et al. 2013. Molecular indicators of microbial diversity in oolitic sands of Highborne Cay, Bahamas. Geobiology 11: 234-251. doi: 10.1111/gbi.12029.

See the publications above (in the dataset description) for detailed methodology.

For accession numbers JX873274 - JX873955, refer to Bernhard et al. 2013 and Edgcomb et al. 2013, ISME Journal.
For accession number KC790540, refer to Bernhard et al. 2013.
For accession numbers JX872558 - JX873273, SRA061992 and SRA061825, refer to Edgcomb et al. 2013, ISME Journal.
For accession numbers JX255738 - JX255917 and JX504252 - JX504530, refer to Edgcomb et al. 2013, Geobiology.

Brief summary of methods:
Samples were collected from Highborne Cay, Bahamas in March 2010 and from Hamelin Pool, Australia in June 2011. Microbialite mat types at Highborne Cay were designated according to Reid et al. (2000) and Myshrall et al. (2010). Microbialites at Hamelin Pool were classified following Jahnert and Collins (2011) and Logan (1961). The water column in the vicinity of the microbialite mats was also sampled. Water column measurments included temperature, salinity, and ligh intensity. Microbialite samples were obtained using syringe cores (refer to publications for sizes and depths).

RNA was extracted from preserved samples, reverse transcribed, and PCR amplified. PCR products were purified and foraminiferal PCR products were cloned for Sanger sequencing. Sequences were clustered into operational taxonomic units (OTUs). JAguc (Nebel et al. 2011) was used to assign taxonomy of OTU representatives. Again, refer to publications above for detailed methodology, statistical analyses, and results.

Collaborative Research: Were Protists the Beginning of the End for Stromatolites?

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Microbial mats are conspicuous components of many benthic marine and aquatic settings. A subset of these microbial mats binds sediments to form potentially fossilizable structures, often called stromatolites or microbialites. While much is known about microbialite autotrophs, little is known about their heterotrophic eukaryotes. The lack of understanding is surprising given that stromatolites have an extensive geologic record spanning most of Earth's history. Stromatolites are layered sedimentary structures formed by a combination of microbial activities, abiotic carbonate precipitation, and sedimentary processes. Details of stromatolite formation and preservation are poorly understood, and a drastic decline in stromatolite occurrence and diversity in the late Precambrian has long been a conundrum. A popular hypothesis to explain this decline at ~1 billion years ago is that eukaryotic organisms evolved to become predators on stromatolites. To date, the most commonly proposed predatory culprit is an unidentified metazoan, although evidence of such an organism is lacking from the fossil record. Protists, most of which are not expected to leave an obvious fossil record, are additional possible stromatolitic predators, but they have been largely ignored in this context. The hypotheses of this project are: (1) Heterotrophic protist activity caused the textural change from stromatolites (layered sediment fabric) to thrombolites (clotted sediment fabric) and (2) Heterotrophic protists caused the decimation of Neoproterozoic stromatolites. Since it is impossible to recreate the Neoproterozoic, studies of modern analogs serve to indirectly test these hypotheses. The overall goal of this project is to describe the eukaryotic communities associated with modern stromatolites and thrombolites from the Bahamas and Australia, compare the communities from the two sites, and to relate the communities to stromatolitic / thrombolitic sediment fabric and biomarker signatures.

The overall goal will be achieved by addressing the following specific aims: (1) Identify, via morphologic and molecular approaches, the eukaryotic community of modern stromatolites and thrombolites; (2) Analyze modern and fossil stromatolites and thrombolites for their eukaryotic lipid biomarkers using solvent extraction, chromatographic and mass spectrometric methods; (3) Using the Fluorescently Labeled Embedded Core (FLEC) method, document the sub-millimeter distributions of the heterotrophic eukaryotic community inhabiting modern stromatolites and thrombolites in conjunction with fine-scale sediment fabric; (4) Using solvent extraction, chromatographic and mass spectrometric methods, analyze cultures of allogromiid foraminifers to survey for lipid biomarkers unique to them; (5) After incubation of modern stromatolites with heterotrophic protists, use FLEC methodology to determine how their activity affects sediment fabric and conduct preliminary comparisons of these modern fabrics to those of stromatolite fossils.

Intellectual Merit: The oldest fossil stromatolites are >3.4 billion years old and are the most visible manifestations of pervasive microbial life on the early Earth. The changes in stromatolite abundance and morphology document complex interplays between biological and geological processes. This project addresses multiple aspects of stromatolite genesis and pre-fossilization alteration but at its core, focuses on one of the greatest geological enigmas: the possible connection between stromatolite decline and the rise of complex life.