Project 1. Study of M. tuberculosis under human host selection to identify virulence and barrier lipids Project Leader: D. Branch Moody Coinvestigators: Kyu Rhee, Jacob Mayfield Collaborating Investigators: Adriaan Minnaard (Core C), Jeremy Rock (Core D), Clare Smith (Core E) ABSTRACT Comparative genomics has served as a dominant paradigm for tracking the tuberculosis (TB) epidemic, understanding Mycobacterium tuberculosis (Mtb) virulence and developing new drugs and diagnostics. Mycobacterial metabolism, in contrast, has been viewed as invariant feature of all clinical Mtb strains. Through comparative metabolomic profiling of ~10,000 lipids among 84 patient-derived Mtb strains, we discovered that Mtb’s pathognomonic lipid envelope shows identifiable patterns of variance among strains circulating among human populations. To determine the impact of phenotypic diversity within the infecting bacterial population, we will map cell wall lipid variation among 140 Mtb strains among TB patients from Masiphulemele, South Africa. The resulting lipid map will describe variations in lipid composition among Mtb strains transmitting in community. From a biological perspective, Mtb’s lipid envelope forms the primary interface with the host and is therefore a direct and ongoing biochemical target of evolutionary selection. This project aims to reveal the previously undescribed chemical diversity and lipid products that have arisen as a consequence of host- and drug-derived clinical pressure. Using organism wide lipid profiling and genome wide sequencing, we have identified 42 lipid-gene pairs that dominate in Mtb strain variance, as well as 1150 lipid species overexpressed in virulent Mtb and 250 lipids selectively expressed at the host interface. Preliminary data support our ability to then link these lipids to specific bacterial genes, even when prior to knowledge of the metabolite’s structure or a gene’s function is lacking. CRISPR interference strategies will then establish causal linkages between genes of unknown function and newly discovered lipids. We will further test lipid deficient strains in collaborative cross mice to reveal specific roles of newly identified lipids in Mtb virulence. These discovery studies will identify biologically important lipids that determine key outcomes in virulence, the host interface and Mtb survival in vivo, supporting new approaches for tuberculosis diagnosis and treatment.