Growth of Biomarkers in Silica Deposits

Silica 1

Biosignatures are the physical or chemical remnants of dead organisms preserved in rocks. Physical evidence such as bones and shells are relatively common and diagnostic of specific species of large organisms. Conversely, microscopic organisms rarely leave physical evidence for scientists to study. Modern silica sinters provide one example where physical evidence of microorganisms can be preserved. Unfortunately, in older sinters other processes can obscure this fossil information and the physical evidence of their existence is usually lost.

Silica 2

However, microbes are composed of numerous types of biomolecules and one group of molecules, called lipids, can resist silicification, thus, although physical evidence can be lost, these diagnostic chemical biomarkers can be preserved. Preserved lipids represent a chemical biosignature of microscopic life and could be used to identify the types of microbes that were present in old sinter samples.

The use of chemical biosignatures in silica sinters may be able to tell us about the physical and chemical conditions operating when the sinters were formed. Even old, inactive sinters could still preserve microbial lipids that can be diagnostic of the ancient microbial population.
In collaboration with the Organic Geochemistry Unit, University of Bristol, GNS Science is studying lipids preserved in silica sinters throughout the Taupo Volcanic Zone. At present, the types of molecular biomarkers produced by different microbes are poorly understood, and physico- chemical controls on expression, incorporation and preservation of biomarkers in sinter deposits are largely unconstrained.

silica 3 graph

Our research uses field and laboratory studies to integrate knowledge of the physico-chemical environment of deposition, microbial diversity (from phylogenetic studies), and analysis of organic biomarkers to determine the relationship between microbial community and trapped biomarkers. This will be the first study of its kind in which geochemical knowledge will be combined with phylogenetic information and biomarker analyses to provide a more complete history of microbial biodiversity.

References
1. Pancost RD, Pressley S, Coleman JM, Benning LG, Mountain BW (2005) Lipid biomolecules in silica sinters: indicators of microbial biodiversity. Environmental Microbiology 7, 66-77.
2. Pancost RD, Pressley S, Coleman JM, Talbot HM, Kelly SP, Farrimond P, Schouten S, Benning L, Mountain BW (2006) Composition and implications of diverse lipids in New Zealand Geothermal sinters. Geobiology 4, 71-92.