• Classes of molecules often have a characteristic fragment ion that can be used to search for those molecules in a total ion current.

  • [4] Use as a lipid biomarker Tetrahymanol has been found in many marine ciliates at relatively high concentrations, suggesting it may be a useful biomarker in the Earth’s
    rock record.

  • Eukaryotes use oxidosqualene cyclase and several other enzymes to create the tetracyclic skeleton found in steroids, a process that requires molecular oxygen.

  • It has been suggested that these organisms may be synthesizing gammacerane in response to other shifting parameters during water column stratification, as most of the bacteria
    that contain the ths gene thrive in dynamic environments.

  • [6] Bacteria use a similar enzyme (shc) to create the pentacyclic hopanoid precursor, diploptene; however, this biosynthesis does not require oxygen.

  • The triterpenoids are a class of molecules found in both bacteria and eukaryotes, which largely make hopanols and sterols, respectively.

  • All three of these molecular classes have structures that lend themselves to membrane rigidity and other, still unknown, physiological functions.

  • [4] Also, alphaproteobacteria present a potentially large source of the lipid in the rock record.

  • It was recently discovered that tetrahymanol-producing bacteria form diploptene using shc then elongate the final cyclopentane into a fifth ring using tetrahymanol synthase

  • The structures of these three classes of molecules are shown below.

  • After growing modern microbes that synthesize tetrahymanol, many of the biomolecules are too polar to separate on GC, so LC is used to characterize the abundance of different

  • MS/MS experiments allow the total ion current to be filtered by both the molecular ion and the characteristic fragment ion of a given molecule.

  • [4] It is unknown whether bacteria modify diploptene into other hopene molecules before creating tetrahymanol.

  • Each molecule has a diagnostic fragmentation pattern in a given ion source.

  • Mass spectrometry characterizes the mass of a given molecule by first fragmenting and ionizing the molecule into smaller carbocations known as daughter ions.

  • [5] After performing an extraction of the rocks with organic solvents, Summons characterized the abundance of various lipid biomarkers using GC-MS/MS, as described above.

  • Ciliates living in these conditions must adapt to produce lipids that do not require molecular oxygen for their biosynthesis.


Works Cited

[‘ Mallory FB, Gordon JT, Conner RL (June 1963). “The Isolation of a Pentacyclic Triterpenoid Alcohol from a Protozoan”. Journal of the American Chemical Society. 85 (9): 1362–1363. doi:10.1021/ja00892a042.
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