(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-06)
Saenz, James P.
Lipids have a legacy in the geologic record extending back to the Archaean.
Since the phylogenetic diversity of life is reflected in the structural diversity
of biomolecules, lipid biomarkers that are shown to be diagnostic of certain
organisms that carry out specific biochemical processes or that are
demonstrated to have unique physiological roles can be used to trace the
biogeochemical influence of bacteria in modern and ancient environments. In
this thesis I explore the application of two classes of bacterial membrane
lipids as biomarkers for marine biogeochemical processes in marine
environments: ladderanes and hopanoids. Through the detection of ladderane
lipids – biomarkers for anaerobic ammonium oxidizing (anammox) bacteria –
I demonstrate the presence and distribution of anammox bacteria in a
subterranean estuary. Through a survey of hopanoids in marine
environments and cultured marine cyanobacteria I show that hopanoids are
ubiquitous in the oceans and that their presence in ancient marine sediments
could provide information about biogeochemical processes in past
environments. Based on novel results demonstrating that hopanoids are
resistant to extraction by non-ionic detergent, I propose that they may play a
role in lipid ordering and the formation of putative lipid rafts in hopanoid-producing
bacteria.
