MME Project: Adaptive significance of marine ammonia-oxidizing archaeal membrane lipids
Marine ammonia-oxidizing archaea (AOA) are among the most ubiquitous and abundant organisms in the ocean and are now recognized to exert a major control over the oxidation state of nitrogen in marine environments. Marine AOA also make a significant contribution to carbon fixation through chemosynthetic pathways, the production of the greenhouse gases nitrous oxide and methane, and the provision of vitamin B12 to B12-dependent populations in oceanic systems. Marine AOA synthesize the glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipids with crenarchaeol, containing a unique cyclohexane ring as the characteristic component. The GDGT membrane lipids form the basis for one of the most commonly employed proxies, the TEX86 proxy, which is used for sea surface temperature reconstructions from the Jurassic to present. Despite widespread application of the TEX86 paleothermometer, mounting evidence suggests that we do not understand the fundamental controls on GDGT distributions in living AOA.
In this project I will investigate the major physiological and environmental controls and the adaptive significance of GDGT compositional plasticity in marine AOA. I will use the most recent technological advances in lipid analysis and high throughput sequencing to evaluate the variation in GDGT distributions among AOA ecotypes across large spatial scales in the ocean. In addition, by combining laboratory and field studies, I will test the influence of environmental and biotic variables on GDGT distributions in pure cultures and natural communities of marine AOA. Finally, I will determine the physical structures and mechanical properties of marine AOA membranes by isolating and characterizing the nanoscale lipid patches with different GDGT compositions and cyclization. Together these studies will determine the fundamental principles controlling the ecophysiology of AOA, advance understanding of their remarkable adaptive capacity in the marine environments, and refine our interpretation of TEX86 records.