Functional characterization of two Anaplasma phagocytophilum genes required for infection of mammalian host and tick vectors, respectively

Anaplasma phagocytophilum is a tick-borne pathogen and the causative agent of Human Granulocytic Anaplasmosis (HGA). A. phagocytophilum is not transovarially transmitted from the mother to the progeny of infected ticks and therefore needs to survive in both a mammalian and the arthropod vector in order to complete its life cycle. To adapt to different environments, A. phagocytophilum relies on differential gene expression as well as the post-translational modification of proteins. However, little is known about what A. phagocytophilum genes and enzymes are required for the infection of human or tick cells. I used random mutagenesis to generate knock-out strains of Ap for functional genomics studies. One of the mutated strains presented an insertion within the coding region of an O-methyltranferase (OMT) family 3, which affects the ability of A. phagocytophilum to infect tick cells. Studies in the function of this enzyme suggest that it is involved in the methylation of an outer membrane protein (Major Surface Protein 4), which appears to be involved in bacterial binding and entry. The second mutant presents an insertion within the coding region of a hypothetical protein in the locus APH_0906 and is unable to infect HL-60 cells and is impaired in its ability to grow in endothelial cells. Localization analysis of the protein showed that the protein is secreted into the cytoplasm and then translocated into the nucleus of host cells. Bioinformatic analyses demonstrated differences in Nuclear Localization Signals (NLSs) as well as binding residues within the protein homolog of human and non-human strains. Herein, I present the results from the functional analyses of both gene products.