AM-19226 is a pathogenic O39 serogroup Vibrio cholerae strain that lacks the typical virulence factors for colonization (toxin-coregulated pilus [TCP]) and toxin production (cholera toxin [CT]) and instead encodes a type III secretion system (T3SS). The mechanism of pathogenesis is unknown, and few effector proteins have been identified. We therefore undertook a survey of the open reading frames (ORFs) within the ϳ49.7-kb T3SS genomic island to identify potential effector proteins. We identified 15 ORFs for their ability to inhibit growth when expressed in yeast and then used a ␤-lactamase (TEM1) fusion reporter system to demonstrate that 11 proteins were bona fide effectors translocated into HeLa cells in vitro in a T3SS-dependent manner. One effector, which we named VopX (A33_1663), is conserved only in V. cholerae and Vibrio parahaemolyticus T3SS-positive strains and has not been previously studied. A vopX deletion reduces the ability of strain AM-19226 to colonize in vivo, and the bile-induced expression of a vopX-lacZ transcriptional fusion in vitro is regulated by the T3SS-encoded transcriptional regulators VttR A and VttR B . An RLM1 yeast deletion strain rescued the growth inhibition induced by VopX expression, suggesting that VopX interacts with components of the cell wall integrity mitogen-activated protein kinase (MAPK) pathway. The collective results show that the V. cholerae T3SS encodes multiple effector proteins, one of which likely has novel activities that contribute to disease via interference with eukaryotic signaling pathways.Vibrio cholerae is the etiologic agent of the severe and potentially lethal diarrheal disease called cholera (31, 49). Although over 200 different serogroups of V. cholerae have been identified, only O1 and O139 serogroup strains cause epidemic and pandemic disease (5, 6, 16). In pathogenic O1 and O139 serogroup isolates, the virulence factors for colonization (toxincoregulated pilus [TCP]) and toxin production (cholera toxin [CT]) are essential, and their expression is controlled by a transcriptional cascade regulated primarily by the transmembrane protein ToxR (36). Strains belonging to other serogroups can also cause disease and are collectively referred to as non-O1/non-O139 serogroup strains. Although they are typically associated with sporadic diarrheal disease, reports of increased incidence of non-O1/non-O139-associated disease suggest that these strains warrant increased attention and may be an emerging threat (17, 47). However, the pathogenic mechanisms of non-O1/non-O139 strains are not as well studied as those of O1 and O139 strains. Recent reports suggest that a type III secretion system (T3SS) is present in a subset of non-O1/non-O139 isolates and represents an important virulence mechanism for some V. cholerae strains (4,8,12,56).T3SSs are commonly found in pathogenic, Gram-negative bacteria, such as Yersinia, Salmonella, Shigella, enteropathogenic/enterohemorrhagic Escherichia coli (EPEC/EHEC), and Pseudomonas. However, T3SS conservation among species is ...

During malaria blood-stage infections, parasites interact with the RBC surface to enable invasion followed by intracellular proliferation. Critical factors involved in invasion have been identified using biochemical and genetic approaches including specific knockdowns of genes of interest from primary CD34 hematopoietic stem cells (cRBCs). Here we report the development of a robust in vitro culture system to produce RBCs that allow the generation of gene knockouts via CRISPR/Cas9 using the immortal JK-1 erythroleukemia line. JK-1 cells spontaneously differentiate, generating cells at different stages of erythropoiesis, including terminally differentiated nucleated RBCs that we term "jkRBCs." A screen of small-molecule epigenetic regulators identified several bromodomain-specific inhibitors that promote differentiation and enable production of synchronous populations of jkRBCs. Global surface proteomic profiling revealed that jkRBCs express all known host receptors in a similar fashion to cRBCs and that multiple strains invade jkRBCs at comparable levels to cRBCs and RBCs. Using CRISPR/Cas9, we deleted two host factors, basigin (BSG) and CD44, for which no natural nulls exist. BSG interacts with the parasite ligand Rh5, a prominent vaccine candidate. A BSG knockout was completely refractory to parasite invasion in a strain-transcendent manner, confirming the essential role for BSG during invasion. CD44 was recently identified in an RNAi screen of blood group genes as a host factor for invasion, and we show that knockout results in strain-transcendent reduction in invasion. Furthermore, we demonstrate a functional interaction between these two determinants in mediating erythrocyte invasion.

Malaria pathogenesis is caused by the replication of Plasmodium parasites within the red blood cells (RBCs) of the vertebrate host. This selective pressure has favored the evolution of protective polymorphisms in erythrocyte proteins, a subset of which serve as cognate receptors for parasite invasion ligands. Recently, the generation of RBCs from immortalized hematopoietic stem cells (HSCs) has offered a more tractable system for genetic manipulation and long‐term in vitro culture, enabling elucidation of the functional determinants of host susceptibility in vitro. Here we report the generation of an immortalized erythroid progenitor cell line (EJ cells) from as few as 100 000 peripheral blood mononuclear cells. It offers a robust method for the creation of customized model systems from small volumes of peripheral blood. The EJ cell differentiation mirrored erythropoiesis of primary HSCs, yielding orthochromatic erythroblasts and enucleated RBCs after eight days (ejRBCs). The ejRBCs supported invasion by both P. vivax and P. falciparum. To demonstrate the genetic tractability of this system, we used CRISPR/Cas9 to disrupt the Duffy Antigen/Receptor for Chemokines (DARC) gene, which encodes the canonical receptor of P. vivax in humans. Invasion of P. vivax into this DARC‐knockout cell line was strongly inhibited providing direct genetic evidence that P. vivax requires DARC for RBC invasion. Further, genetic complementation of DARC restored P. vivax invasion. Taken together, the peripheral blood immortalization method presented here offers the capacity to generate biologically representative model systems for studies of blood‐stage malaria invasion from the peripheral blood of donors harboring unique genetic backgrounds, or rare polymorphisms.

Vibrio cholerae is a genetically diverse species, and pathogenic strains can encode different virulence factors that mediate colonization and secretory diarrhea. Although the toxin-coregulated pilus (TCP) is the primary colonization factor in epidemic-causing V. cholerae strains, other strains do not encode the TCP and instead promote colonization via the activity of a type 3 secretion system (T3SS). Using the infant mouse model and T3SS-positive O39 serogroup strain AM-19226, we sought to determine which of 12 previously identified, T3SS-translocated proteins (Vops) are important for host colonization. We constructed inframe deletions in each of the 12 loci in strain AM-19226 and identified five Vop deletion strains, including ⌬VopM, which were severely attenuated for colonization. Interestingly, a subset of deletion strains was also incompetent for effector protein transport. Our collective data therefore suggest that several translocated proteins may also function as components of the structural apparatus or translocation machinery and indicate that while VopM is critical for establishing an infection, the combined activities of other effectors may also contribute to the ability of T3SS-positive strains to colonize host epithelial cell surfaces. The toxin-coregulated pilus (TCP) is the major colonization factor encoded by all pathogenic O1 and O139 serogroup Vibrio cholerae strains, which cause epidemic cholera. In contrast, most clinically isolated non-O1/non-O139 serogroup strains do not encode TCP and thus must employ other mechanisms to effectively colonize the human intestinal epithelium and cause sporadic, cholera-like disease (1-3). Genome sequence analysis of a clinically isolated O39 serogroup strain, named AM-19226, identified a pathogenicity island on the large chromosome that encodes the structural proteins for a type 3 secretion system (T3SS) (4). T3SSs function as principal virulence mechanisms in many Gram-negative bacterial pathogens (e.g., Escherichia, Salmonella, Pseudomonas, Shigella, and Yersinia spp.), and in vivo studies using different animal models confirmed that the V. cholerae T3SS is essential for causing disease (5-7). In addition, numerous groups have identified T3SS-positive V. cholerae strains in laboratory collections, from patients, and from endemic environments, suggesting that a subset of non-O1/non-O139 serogroup strains depends on T3SS activity for virulence (1,3,4,(8)(9)(10).The V. cholerae T3SS is most closely related to the Vibrio parahaemolyticus T3SS2. T3SS2 is associated with pandemic V. parahaemolyticus strains, whereas T3SS1 is present in all strains (11). Comparison of the T3SS genomic islands in V. cholerae strain AM-19226 and V. parahaemolyticus strain RIMD2210633 reveals synteny within a conserved, central "core" region, flanked by 5= and 3= regions of greater coding diversity between clades and species (4, 10, 12-14). The core region encodes proteins that form the T3SS structural apparatus and is transcriptionally organized into four main operons in V. cholera...

Plasmodium vivax has two invasion ligand/host receptor pathways (PvDBP/DARC and PvRBP2b/TfR1) that are promising targets for therapeutic intervention. We optimized invasion assays with isogenic cultured reticulocytes. Using a receptor blockade approach with multiple P. vivax isolates, we found that all strains utilized both DARC and TfR1, however with significant variation in receptor usage. This suggests that P. vivax, like P. falciparum, uses alternative invasion pathways with implications for pathogenesis and vaccine development.