Molecular indicators (biomarkers) of past life

Abstract

Biomarkers in geological samples on Earth are products derived from biochemical precursors (i.e., natural products) by reductive and oxidative alteration processes (e.g., cholestanes from cholesterol). Generally, lipids, pigments, and some biomembranes are preserved best over longer geological times, and labile compounds such as amino acids, sugars, etc. are useful biomarkers for recent times. Thus, the detailed characterization of biomarker composition permits the assessment of the major contributing species of extinct and/or extant life. Nonbiomarkers and abiogenic organic compounds are also discussed. In the case of the early Earth, work has progressed to elucidate biomarker structures and carbon isotopic signals preserved in ancient sedimentary rocks. In addition, the combination of bacterial biochemistry with the organic geochemistry of contemporary and ancient hydrothermal ecosystems permits the modeling of the nature, behavior, and preservation potential of primitive microbial communities. This approach entails combined molecular and isotopic analyses to characterize lipids and biopolymers produced by cultured bacteria (representative of ancient strains) and to test a variety of culture conditions that affect their biosynthesis processes. In regards to Mars, the biomarkers from lipids and biopolymers would be expected to be preserved best if life flourished there during its early history (3.5-4 ϫ 10 9 years ago). Both oxidized and reduced products would be expected. This is based on the inference that hydrothermal activity occurred during that time, with the concomitant preservation of biochemically-derived carbonaceous matter. Known biomarkers (i.e., as elucidated for early terrestrial samples and for primitive terrestrial microbiota) as well as novel, potentially unknown compounds, should be characterized. Anat

Preservation of Microbial Lipids in Geothermal Sinters

“…Their structures have been w ell p re served th ro u g h o u t geological tim e, such th at they have been extensively utilized as indictors of p ast biological activity on E arth (e.g., Sum m ons et a l, 1996;Freeman, 2001;H ayes, 2001;Simoneit, 2002) an d in som e cases u sed to characterize past m icrobial com m unities (e.g., Thiel et a l, 2001; Peckm ann an d Thiel, 2004;Brocks et at., 2005;Birgei et at., 2006). Recently, it w as show n th at lipid biom arkers ap p ear to b e w ell preserved in geotherm al sinters, w ith rap id silicification aiding geo chemical preservation (Pancost et a l, 2005(Pancost et a l, , 2006Talbot et a l, 2005;G ibson et a l, 2008;K aur et a l, 2008), an d it w as p ro po sed th at such com pounds, once encased in the silica m a trix, could persist for extended periods of time.…”

In Vitro Selection of Functional Oligonucleotides and the Origins of Biochemical Activity

“…The historical record does not provide many details about how early life forms worked; it only hints at what their compositions might have been (Simoneit, 2002). Deconstructing and minimizing existing organisms such as Mycoplasma (Smith et al, 2003;Check, 2002) will only tell us about cells containing DNA, RNA, and protein that are many times more complicated than the first were likely to have been.…”

A review of current applications of mass spectrometry for biomarker/molecular tracer elucidations

“…Oxidized and reduced products would both be expected. The most versatile and specific methods available now for biomarker characterization are based on mass spectrometry (Simoneit, 2002b).…”