Graduation Date

Spring 5-10-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Programs

Genetics, Cell Biology & Anatomy

First Advisor

Stacey D. Gilk

Abstract

Coxiella burnetii is a highly infectious and environmentally persistent bacterium that causes the disease Q Fever. Its intracellular home, the Coxiella-Containing Vacuole (CVV), is formed from fusion of host-derived vesicles and is rich in sterols - yet cholesterol accumulation in the CCV is bacteriolytic. Our lab’s goal is to understand how Coxiella manages intracellular cholesterol levels and survives within the host. One way Coxiella may modulate CCV cholesterol is through membrane contact sites (MCS), areas where molecular complexes bridge two organelles and exchange lipids. This thesis explores how Coxiella uses both a mammalian lipid transfer protein and bacterially-encoded effector proteins to control MCS with the endoplasmic reticulum (ER). The mammalian protein, ORP1L, localizes to the CCV and mediates CCV-ER MCS. ORP1L localization depends on the Coxiella Type 4B Secretion System (T4BSS), which secretes bacterial effector proteins into the host cytosol to manipulate pathways and increase bacterial survival. I showed that Coxiella uses ORP1 to lower CCV cholesterol and increase bacterial growth in macrophages. Additionally, our lab identified nine Coxiella T4BSS effector proteins with putative FFAT motifs, special protein sequences that indicate potential interaction with VAPs, a family of ER proteins known to form MCS. I found that one of these proteins, CBU1751, interacts with VAPA and VAPB through a two-hybrid assay but not by co-immunoprecipitation. Future work will clarify the mechanism by which ORP1 lowers CCV cholesterol and interrogate whether CBU1751 interacts with VAPs to form plasma membrane-ER MCS.

Comments

2025 Copyright, the authors

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