Stanford University

Due to COVID-19, all classes have moved to an online format and many events at Stanford have been canceled or moved to a virtual format. This calendar may not reflect all changes. Please confirm event status with the event contact before attending.


ESS Ph.D. Defense: Environmental relevance and physiological By Marisa Mayer

Friday, May 14, 2021 11:00 AM
More Info:
ESS Ph.D. Defense: Environmental relevance and physiological By Marisa Mayer


Faculty/Staff, Students, Alumni/Friends
Department of Earth System Science


This dissertation research seeks to utilize for laboratory and field techniques to uncover meaning behind the occurrence of 3-methylhopanoids in an anoxygenic phototroph. We are interested in how the addition of such a metabolically unique organism and the environmental context of such an uncommon poster child for an extreme environment will influence future studies and interpretations of both rock record and modern ecosystems. To answer new interpretations of 3-methylhopanoid rock record significance, we chose to study this new lineage of 3-methyhopanoid producers in laboratory cultures (CHAPTER 1), in situ from the environments that this strain was directly isolated from (CHAPTER 2), and in silico through the metagenomic data of other hot springs and an expanding list of environments in which the PNS call home (CHAPTER 3). This work indicates that PNS bacteria are potential sources of 3-methylhopanoids in both laboratory and direct environmental settings and thus should be considered along with methanotrophs, and the more rarely indicated acetic acid bacteria, when interpreting modern and ancient sedimentary biomarker records. The three chapters of this Dissertation that explore this topic are summarized below:


Bacterial lipids are well preserved in ancient rocks and certain ones have been used as indicators of specific bacterial metabolisms or environmental conditions existing at the time of rock deposition. Here we show that an anaerobic bacterium produces 3-methylbacteriohopanepolyols (3-MeBHPs), pentacyclic lipids previously detected only in aerobic bacteria and widely used as biomarkers for methane-oxidizing bacteria. Both Rhodopila globiformis, a phototrophic purple nonsulfur bacterium isolated from an acidic warm spring in Yellowstone, and a newly isolated Rhodopila species from a geochemically similar spring in Lassen Volcanic National Park (USA), synthesized 3-MeBHPs and a suite of related BHPs and contained the genes encoding the necessary biosynthetic enzymes. Our results show that 3-MeBHPs can be produced under anoxic conditions and challenges the use of 3-MeBHPs as biomarkers of oxic conditions in ancient rocks and as prima facie evidence that methanotrophic bacteria were active when the rocks were deposited.

2019 Webby Award Nominee

IconsList of icons used on the sitemaillinkedindouble carrot leftarrow leftdouble carrotplayerinstagramclosecarrotquotefacebooktwitterplusminussearchmenuarrowcloudclock