Uncovering novel cholesterol-protein interactions in cholesterol-producing and cholesterol-utilizing bacteria

/Abstract All living organisms, from the simplest microbes to complex humans, produce lipids. Lipids are a broad class of organic molecules that include, among others, fatty acids, cholesterol, and isoprenoids. Lipids play critical roles in membrane structure, cell signaling, and cell development and have been of interest to a broad range of scientists. Biochemists have elucidated the elegant biochemical reactions and pathways required to synthesize them, physiologist have uncovered various structural and functional roles of lipids, and geologist have shown that the recalcitrant nature of lipids makes them excellent molecular fossils that can inform our understanding of the ancient Earth’s ecosystems. In my research group, we have focused on understanding the biosynthesis of lipids in microbes with the primary goal of revealing novel lipid producers, new lipid structures, and distinct biosynthetic pathways. Through our work, we have made significant discoveries in lipid biosynthesis – from revealing that archaea utilize unique radical chemistry to modify their distinct isoprenoid membranes to discovering de novo synthesis of cholesterol in bacterial species. Over the next five years, we would like to build on the foundation of these insights to move beyond studying lipid biosynthesis to lipid function, regulation, and transport in these microbes with a particular focus on sterols in bacteria. Sterol lipids are essential and ubiquitous components of all eukaryotic cells. The most well-studied sterol is cholesterol, the primary sterol produced by vertebrates and a key lipid in human health. High levels of cholesterol are linked to increased risks of cardiovascular disease and impaired cholesterol trafficking has been implicated in a variety of defects including lysosomal storage diseases. Further, bacterial-cholesterol interactions within the human host have been proposed to affect human lipid metabolism, through the gut microbiome, and are critical for infection by a variety of intracellular bacterial pathogens. However, the molecular mechanisms involved in bacterial-cholesterol interactions, particularly in the context of human health, are not fully understood. Interestingly, while certain bacteria can metabolize human host cholesterol, these bacteria cannot produce cholesterol themselves. Indeed, no bacterium, whether host-associated or free-living, was thought to produce cholesterol de novo. My research group recently demonstrated the first instance of de novo cholesterol biosynthesis in bacteria, and we have identified potential molecular links in cholesterol-producing bacteria to cholesterol metabolism by human-associated gut bacteria. We now seek to explore the molecular mechanisms driving bacterial-cholesterol interactions in bacteria that produce cholesterol and bacteria that metabolize cholesterol - two distinct bacterial groups that could provide broad insight into unknown biological pathways impacted by cholesterol as well as potentially uncovering novel sterol regulatory and transport mechanisms. Ultimately, we aim to further explore cholesterol metabolism in more complex microbiome communities with the goal of developing strategies to reshape microbiomes for beneficial outcomes. Project Number: 1R35GM161274-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of General Medical Sciences (NIGMS) | Principal Investigator: Paula Welander | Institution: STANFORD UNIVERSITY, STANFORD, CA | Award Amount: $440,750 | Activity Code: R35 | Study Section: Maximizing Investigators' Research Award - F Study Section[MRAF] View on NIH RePORTER: https://reporter.nih.gov/project-details/11259046