CSIRO Marine and Atmospheric Research
Past Seminars

Tuesday 4 November 2003, 11.30am (Tas time)

CSIRO Auditorium, Hobart

Marco J. L. Coolen
Royal Netherlands Institute for Sea Research,
Department of Geobiological and Environmental Chemistry

Lipid and fossil rDNA stratigraphy reveals impact of environmental changes on the ancient microbial community of meromictic, euxinic Ace Lake (Antarctica)

Antarctic Ace Lake was originally a melt-water freshwater lake that became saline due to connection to the sea resulting from the Holocene deglaciation and subsequent became isolated due to isostatic rebound of the Antarctic continent. After its isolation, melt water was introduced causing stratification of the water column and the formation of bottom water anoxia. We expected that these climate-induced variations in the chemical and physical characteristics of the water column would have had a great impact on the diversity and abundance of species, which thrived in the ancient water column of Ace Lake. Fossilized organic components provide an archive of ancient aquatic microbial communities and, hence, can be used to reconstruct variations in climate and its impacts on biodiversity. However, the interpretation of these data is complicated by the often limited specificity of traditional biomarkers, such as lipids and pigments. The ultimate biomarkers are ribosomal RNA genes, which sequences provide information at the species level by phylogenetic comparison. It was generally believed, however, that labile biomacromolecules such as DNA become rapidly degraded within sediments. However, during recent years, it has been shown that delicate biomacromolecules like DNA can survive in the fossil record if preservation conditions are optimal. Optimal conditions for the preservation of DNA such anoxic, sulfidic conditions and low in situ temperatures prevail in Ace Lake.

In this seminar, the fate of DNA within the sedimentary record will be discussed. A detailed, combined lipid and rDNA stratigraphy was used to reconstruct the prokaryotes involved in anoxygenic photosynthesis and the cycling of methane during the development of Ace Lake. Furthermore, the quantitative comparison of alkenones and alkenoates, specific biomarkers of marine and brackish haptophyte algae, and the various fossil phylotypes of haptophytes enabled for the first time the identification of sources and their biomarkers at the species level. These results were compared with lipid and rDNA analysis from particulate organic matter collected from vertical positions of the extant water column of Ace Lake.

Authors:

Marco J. L. Coolen1, Gerard Muyzer1,2, Stefan Schouten1, John K. Volkman3, Jaap S. Sinninghe Damsté1

1 Royal Netherlands Institute for Sea Research, Department of Geobiological and Environmental Chemistry, P.O. Box 59, 1790 AB Den Burg, The Netherlands.
2 Present address: Kluyver Laboratory for Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands.
3 Antarctic CRC and CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania 7001, Australia.

References:

Rankin, L. M., J. A. E. Gibson, P. D. Franzmann, and H. R. Burton. 1996. The chemical stratification and microbial comunities of Ace Lake, Antarctica: A review of the characteristics of a marine-derived meromictic lake. Polarforschung 66:33-52.

Coolen, M. J. L., and J. Overmann. 1998. Analysis of subfossil remains of purple sulfur bacteria in a lake sediment. Appl. Environm. Microbiol. 64:4513-4521.

Coolen, M. J. L. 2001. 217,000 year-old DNA sequences indicate different origins of green sulfur bacteria in Mediterranean sapropels Ph.D. thesis, University of Oldenburg, Germany, pp. 114-126.

Willerslev, E. et al. 2003. Diverse plant and animal genetic records from Holocene and Pleistocene sediments. Science 300:791-795.

Volkman, J.K., Eglinton, G., Corner, E.D.S., and T.E.V. Forsberg. 1980. Long-chain alkenes and alkenones in the marine coccolithophorid Emiliania Huxleyi. Phytochem. 19:2619-2622.

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