Date of Award

Fall 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological Science

First Advisor

Daoguo Zhou

Committee Chair

Daoguo Zhou

Committee Member 1

Robert Geahlen

Committee Member 2

Zhao-Qing Luo

Committee Member 3

Claudio Aguilar


Salmonella spp. are gram negative bacteria capable of infecting a number of eukaryotic hosts. In humans, Salmonella infection can range anywhere from acute gastroenteritis to typhoid fever which can oftentimes be fatal.Salmonella are facultative intracellular pathogens that have acquired the ability to enter non-phagocytic cells such as those lining the intestinal epithelium. Uptake into epithelial cells is mediated by the Salmonellapathogenicity island 1 (SPI1) encoded type III secretion system (T3SS), a needle-like complex composed of over 20 proteins that translocates effector proteins directly into the host cell cytosol. Salmonella possess a second type III secretion system encoded on Salmonella pathogenicity island 2 (SPI2) that secretes effector proteins involved in Salmonella containing vacuole (SCV) formation, maturation, and intracellular survival. ^ Entrance into epithelial cells is modulated by effector proteins SopE, SopE2 and SopB. SopE and SopE2 having 69% sequence identity are known to be guanine nucleotide exchange factors (GEFs). SopE is a GEF capable of activating both Rac1 and Cdc42 while SopE2 activates Cdc42 only. SopB is a known phosphatidylinositol phosphate phosphatase possessing both 4- and 5-phosphatase activities promoting membrane ruffling and invasion. The mechanisms through which SopB utilizes its phosphatase activities to mediate membrane ruffling and invasion are still unclear. Previous research has demonstrated that SopB is responsible for the production of PtdIns(3)P at the Salmonella induced ruffles, but the mechanism through which SopB acts is still not understood. This work will directly link the phosphatase activity of SopB, demonstrating the requirement of both the 4- phosphatase and 5-phosphatase activities, to ruffle formation and invasion. We found that the 5-phosphatase activity is responsible for generating PtdIns(3,4)P2 which recruits host SNX9, a protein involved in actin modulation to the plasma membrane. The 4-phosphatase activity of SopB is solely responsible for the hydrolysis of host PtdIns(3,4)P2 into PtdIns(3)P which accumulates around the ruffles and becomes incorporated into the forming SCV membrane. Either activity alone does not result in ruffling or invasion, but when acting in conjunction with one another, the 4-phosphatase and 5-phosphatase activities of SopB lead to SNX9- mediated ruffling and Salmonella invasion.