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

Sáenz, J. P. (2010) PhD thesis, MIT/WHOI Joint Program in Chemical Oceanography.

Summary

This PhD thesis explores the application of two classes of bacterial membrane lipids — ladderanes and Hopanoids — as biomarkers for marine biogeochemical processes. We demonstrated the presence and distribution of anammox bacteria in a subterranean estuary through detection of ladderane lipids. A survey of Hopanoids in marine environments and cultured marine cyanobacteria showed that these lipids are ubiquitous in the oceans and that their presence in ancient marine sediments provides information about past biogeochemical processes. Results showing that hopanoids resist extraction by non-ionic detergent led to the proposal that they play a role in lipid ordering and the formation of putative lipid rafts in hopanoid-producing bacteria.

Key Findings

• Ladderane lipids confirmed the presence and distribution of anammox bacteria in a subterranean estuary, establishing these lipids as reliable biomarkers for anaerobic ammonium oxidation in coastal environments
• Hopanoids are ubiquitous in the oceans, detected across marine environments and cultured marine cyanobacteria including [[crocosphaera-watsonii|Crocosphaera watsonii]]
• Hopanoids resist extraction by non-ionic detergent (Triton X-100), analogous to the detergent-resistant membrane (DRM) behavior of cholesterol — providing the first evidence for a hopanoid-sterol functional analogy in membrane organization
• The hopanoid distribution in ancient marine sediments can trace biogeochemical processes in past environments

Significance

This thesis laid the groundwork for the Hopanoid-Sterol Analogy, connecting observations of hopanoid detergent resistance to a potential role in lipid ordering and domain formation. It represents the foundational work from which subsequent studies on Diplopterol membrane ordering and Bacteriohopanepolyols distribution emerged.