Abstract
Anaplasma phagocytophilum is an emerging zoonotic pathogen transmitted by Ixodes scapularis that causes human granulocytic anaplasmosis. Here, a high throughput quantitative proteomics approach was used to characterize A. phagocytophilum proteome during rickettsial multiplication and identify proteins involved in infection of the tick vector, I. scapularis. The first step in this research was focused on tick cells infected with A. phagocytophilum and sampled at two time points containing 10–15% and 65–71% infected cells, respectively to identify key bacterial proteins over-represented in high percentage infected cells. The second step was focused on adult female tick guts and salivary glands infected with A. phagocytophilum to compare in vitro results with those occurring during bacterial infection in vivo. The results showed differences in the proteome of A. phagocytophilum in infected ticks with higher impact on protein synthesis and processing than on bacterial replication in tick salivary glands. These results correlated well with the developmental cycle of A. phagocytophilum, in which cells convert from an intracellular reticulated, replicative form to the nondividing infectious dense-core form. The analysis of A. phagocytophilum differentially represented proteins identified stress response (GroEL, HSP70) and surface (MSP4) proteins that were over-represented in high percentage infected tick cells and salivary glands when compared to low percentage infected cells and guts, respectively. The results demonstrated that MSP4, GroEL and HSP70 interact and bind to tick cells, thus playing a role in rickettsia-tick interactions. The most important finding of these studies is the increase in the level of certain bacterial stress response and surface proteins in A. phagocytophilum-infected tick cells and salivary glands with functional implication in tick-pathogen interactions. These results gave a new dimension to the role of these stress response and surface proteins during A. phagocytophilum infection in ticks. Characterization of Anaplasma proteome contributes information on host-pathogen interactions and provides targets for development of novel control strategies for pathogen infection and transmission.
Highlights
Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae) is a tick-borne pathogen that is the etiologic agent of human, canine and equine granulocytic anaplasmosis and tick-borne fever of ruminants [1,2,3]
We characterized A. phagocytophilum proteome during rickettsial multiplication in I. scapularis cultured tick cells, guts and salivary glands and demonstrated that this bacterium uses certain stress response and surface proteins to favor pathogen infection and multiplication
The results showed that major surface protein 4 (MSP4), HSP70 and GroEL were recognized at higher levels in infected than in uninfected tick cells while for superoxide dismutase (SOD) differences were not statistically significant between samples, corroborating that MSP4, HSP70 and GroEL proteins were produced at higher levels in high percentage infected tick cells (Fig 3D)
Summary
Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae) is a tick-borne pathogen that is the etiologic agent of human, canine and equine granulocytic anaplasmosis and tick-borne fever of ruminants [1,2,3]. Despite this organism being an emerging zoonotic pathogen in many regions of the world, vaccines are not available for prevention of transmission and infection of humans and animals [4]. Proteomics characterization of Anaplasma spp. provides information on host-pathogen interactions and suggests possible targets for the control of pathogen infection and transmission [17,18,19,20,21,22,23,24,25,26]
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