Exploring the distribution and physiological roles of bacterial membrane lipids in the marine environment

Abstract

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.