Magda Beier-Sexton

University of Maryland, Baltimore | UMB · Department of Microbiology and Immunology

Rickettsia species are Gram-negative obligate intracellular bacteria that infect a wide range of eukaryotes and vertebrates. In particular, human body louse-borne Rickettsia prowazekii and flea-borne Rickettsia typhi have historically plagued humankind and continue to reemerge globally. The unavailability of vaccines and limited effectiveness of an...

Reductive genome evolution has purged many metabolic pathways from obligate intracellular Rickettsia (Alphaproteobacteria; Rickettsiaceae). While some aspects of host-dependent rickettsial metabolism have been characterized, the array of host-acquired metabolites and their cognate transporters remains unknown. This dearth of information has thwarte...

Rickettsia species are obligate intracellular bacteria with both conserved and lineage-specific strategies for invading and surviving within eukaryotic cells. One variable component ofRickettsiabiology involves arthropod vectors: for instance, typhus group rickettsiae are principally vectored by insects (i.e., lice and fleas), whereas spotted fever...

Rickettsiae are obligate intracellular pathogens that induce their uptake into non-phagocytic cells; however, the events instigating this process are incompletely understood. Importantly, diverse Rickettsia species are predicted to utilize divergent mechanisms to colonize host cells, as nearly all adhesins and effectors involved in host cell entry...

Many prokaryotes utilize type IV secretion systems (T4SSs) to translocate substrates (e.g., nucleoprotein, DNA, protein) across the cell envelope, and/or to elaborate surface structures (i.e., pili or adhesins). Among eight distinct T4SS classes, P-T4SSs are typified by the Agrobacterium tumefaciens vir T4SS, which is comprised of 12 scaffold compo...

Bacterial Sec7-domain-containing proteins (RalF) are known only from species of Legionella and Rickettsia, which have facultative and obligate intracellular lifestyles, respectively. L. pneumophila RalF, a type IV secretion system (T4SS) effector, is a guanine nucleotide exchange factor (GEF) of ADP-ribosylation factors (Arfs), activating and recru...

Bacteria of the order Rickettsiales (Alphaproteobacteria) are gram-negative, small, rod-shaped, and coccoid, with all described species existing as obligate intracellular parasites of a wide range of eukaryotic organisms (Gillespie et al. 2012b). Before the DNA revolution, bacteria were assigned to Rickettsiales based primarily on chemical composit...

Phylogeny estimation of Rickettsia Pat1 and Pat1-like patatin phospholipases (cd07199). The conserved domain cd07199 includes PNPLA8, PNPLA9, and Pat17 patatin-like phospholipases. See text for alignment and tree-building methods. Tree is final optimization likelihood: (−61591.367104) using WAG substitution model with GAMMA and proportion of invari...

NCBI and PATRIC accession numbers for Rickettsia Pat1 and Pat2 sequences. (PDF)

Purified recombinant proteins for phospholipase A2 assay. Imperial Protein Stained (Pierce) 4 to 12% Tris-glycine precast gel (Invitrogen) using 1×Tris-glycine-SDS running buffer (BioRad). Purified recombinant proteins (including C-terminal myc epitope and 6×His tag) expressed in E. coli TOP10 cells shown: Lane 1, Pat2 (70.2 kD from pTrc-522HS); La...

The long-standing proposal that phospholipase A2 (PLA2) enzymes are involved in rickettsial infection of host cells has been given support by the recent characterization of a patatin phospholipase (Pat2) with PLA2 activity from the pathogens Rickettsia prowazekii and R. typhi. However, pat2 is not encoded in all Rickettsia genomes; yet another unch...

Rickettsia typhi, the causative agent of murine (endemic) typhus, is an obligate intracellular pathogen with a life cycle involving both vertebrate and invertebrate hosts. In this study, we characterized a gene (RT0218) encoding a C-terminal ankyrin repeat domain-containing protein, named Rickettsia ankyrin repeat protein 1 (RARP-1), and identified...

A defining facet of tick-Rickettsia symbioses is the molecular strategy employed by each partner to ensure its own survival. Ticks must control rickettsial colonization to avoid immediate death. In the current study, we show that rickettsial abundance in the tick midgut increases once the expression of a Kunitz-type serine protease inhibitor from t...

In contrast to 15 or more validated and/or proposed tick-borne spotted fever group species, only three named medically important rickettsial species are associated with insects. These insect-borne rickettsiae are comprised of two highly pathogenic species, Rickettsia prowazekii (the agent of epidemic typhus) and R. typhi (the agent of murine typhus...

Vero cells are derived from the kidney of an African green monkey, and are one of the more commonly used mammalian continuous cell lines in microbiology and molecular and cell biology research. This unit includes protocols for the growth and maintenance of Vero cell lines in a research laboratory setting.

This unit includes protocols for the laboratory maintenance of the obligate intracellular bacterium Rickettsia rickettsii, including propagation in mammalian cell cultures, as well as isolation, counting, and storage procedures. Regulations for working with R. rickettsii in biosafety level 3 containment are also discussed.

Comparative genomic analysis of five pathogenetic bacteria harboring plasmids with associated virulence factors. (0.07 MB DOC)

Background: The genome sequence of Rickettsia felis revealed a number of rickettsial genetic anomalies that likely contribute not only to a large genome size relative to other rickettsiae, but also to phenotypic oddities that have confounded the categorization of R. felis as either typhus group (TG) or spotted fever group (SFG) rickettsiae. Most i...

Lipoprotein processing by the type II signal peptidase (SPase II) is known to be critical for intracellular growth and virulence for many bacteria, but its role in rickettsiae is unknown. Here, we describe the analysis of lspA, encoding a putative SPase II, an essential component of lipoprotein processing in gram-negative bacteria, from Rickettsia...

To understand further the molecular basis of rickettsial host cell invasion, Rickettsia prowazekii invasion gene homolog (invA) has been characterized. Our previous experiments have shown that InvA is an Ap5A pyrophosphatase, a member of the Nudix hydrolase family, which is up-regulated during the internalization, early growth phase, and exit steps...

The groESL operon from an obligate, intracellular, Gram-negative bacterium Rickettsia typhi, the etiologic agent of murine typhus, was cloned and sequenced. The sequence analysis of 2229 bp of the groESL operon reveals two open reading frames of 288 nucleotides (groES) and 1653 nucleotides (groEL) separated by 20 nucleotides. The deduced amino acid...

Application of molecular diagnostic technology in the past 10 years has resulted in the discovery of several new species of pathogenic rickettsiae, including Rickettsia felis. As more sequence information for rickettsial genes has become available, the data have been used to reclassify rickettsial species and to develop new diagnostic tools for ana...

The existence of intracellular rickettsiae requires entry, survival, and replication in the eukaryotic host cells and exit to initiate new infection. While endothelial cells are the preferred target cells for most pathogenic rickettsiae, infection of monocytes/macrophages may also contribute to the establishment of rickettsial infection and resulti...

Rickettsia typhi, the causative agent of murine typhus, grows directly within the host cell cytoplasm, accumulating a large number of progeny, and eventually lyses the cells. Typhus group rickettsiae (R. typhi and R. prowazekii) adhere to and lyse human and sheep erythrocytes. However, the molecular mechanism underlying erythrocyte lysis by R. typh...