SUMMARY Orientia tsutsugamushi is a genetically intractable obligate intracellular bacterium that causes scrub typhus, a globally emerging infection with a high fatality rate. Disease progression depends on bacterial-driven modulation of host antimicrobial responses that affords O. tsutsugamushi the ability to survive in leukocytes and endothelial cells. The bacterial mechanisms responsible are largely unknown, highlighting a gap in our knowledge of host- pathogen interactions that influence scrub typhus outcome. A family of eukaryotic-like effectors called Anks are key O. tsutsugamushi virulence factors. Most consist of an N-terminal ankyrin repeat (AR) domain that mediates protein-protein interactions with host targets and a C-terminal F-box that recruits the host SCF E3 ubiquitin ligase complex to ubiquitinate the AR-bound proteins. The interacting partners and cellular processes that the Anks modulate are mostly unknown. We discovered that O. tsutsugamushi Ank13 is a nucleomodulin. Gene expression profiles in cells ectopically expressing Ank13 recapitulate many of those observed for O. tsutsugamushi infected host cells, indicating that Ank13 contributes to the pathogen’s ability to modulate cellular processes at the transcriptional level. Both infected and Ank13-expressing cells exhibit down-regulation of genes involved in immune responses and other processes regulated by the Notch signaling pathway. A yeast two- hybrid screen coupled with co-immunoprecipitation identified host MIB1 as an Ank13 binding partner. MIB1 is a positive regulator of canonical Notch signaling. MIB1 levels are reduced in O. tsutsugamushi infected cells, and this is phenocopied in cells ectopically expressing Ank13 or an Ank13 mutant with a functionally inactivated F- box. These data suggest that Ank13 sequestration of MIB1 promotes its auto-ubiquitination and proteasomal degradation during infection. Notch ligand surface presentation on infected cells is altered and Notch-related gene ex