PRIMARY FACULTY

Anthony Maurelli, Ph.D.
Professor
Microbiology & Immunology

4301 Jones Bridge Road
Bethesda MD 20814
Office: 301-295-3415
Fax: 301-295-1996
amaurelli@usuhs.mil

Molecular Genetic Analysis of the Pathogenic Mechanisms of Shigella and Chlamydia

The major research interest of this laboratory is the molecular genetics of bacterial pathogenesis. Specifically, we study two intracellular pathogens: Shigella flexneri, a facultative intracellular pathogen and Chlamydia trachomatis, an obligate intracellular pathogen. Shigella are the causative agents of bacillary dysentery, a disease of major importance in many parts of the developing world. Organisms of the genus Chlamydia cause a variety of diseases including pneumonia, blinding eye infections, and sexually transmitted diseases. Our current studies on Shigella flexneri focus on four areas: anti-apoptosis and intracellular survival; intracellular metabolism; and cell signaling via secretion of the Osp effector proteins. We recently characterized the ability of Shigella to block induction of apoptosis in epithelial cells that the bacteria invade and we are defining the bacterial genes involved in anti-apoptosis and identifying the elements of the host apoptosis/survival pathway with which these bacterial proteins interact. The second area of post invasion pathogenesis is focused on metabolic virulence genes, i.e. genes that are specifically required for pathogen growth within the cytoplasm of mammalian cells. We are interested in determining how Shigella grows intracellularly, what nutrients present in the host cytosol are the preferred substrates and what pathways the bacterium uses to metabolize these nutrients. The third area of post invasion pathogenesis is to understand how Shigella modulates the host inflammatory response to bacterial invasion. We recently identified a secreted effector protein, OspF, as a mediator of this response and are studying several other secreted effectors of Shigella that contribute to the bacterium's ability to both induce and dampen the inflammatory response. The fourth area of research is the study of how Shigella evolved from a non-pathogenic ancestor it shared with Escherichia coli to become a pathogen. These studies begin with the concept of pathoadaptation through loss of gene function. As the newly evolved pathogen adapted to its new niche, Shigella lost genes that are incompatible with virulence via deletion ("black holes"), insertion or point mutations. When these genes are re-introduced into Shigella, virulence becomes attenuated. The identification and study of these "anti-virulence" genes provides new avenues for understanding pathogenesis and opens up possibilities for the development of new treatments for dysentery as well as safer vaccine strains.
 
A major barrier to understanding how Chlamydia can cause such a broad range of diseases is the absence of genetic tools for studying the organism. An important focus of our efforts over the past 10 years has been to develop these tools so that the power of molecular genetics can be applied to understanding Chlamydia pathogenesis. We have recently demonstrated allelic exchange in C. psittaci and isolated stable recombinants. This step is a critical first step and we continue to be committed to developing genetic tools for Chlamydia. In addition, we are using a variety of biochemical and molecular approaches to increase our understanding of Chlamydia biology. One project is to define the steps in peptidoglycan synthesis in Chlamydia and determine the role that peptidoglycan plays in the developmental cycle of the organism. Another project is focused on elucidating the pathways of synthesis or acquisition of essential metabolic intermediates and /or cofactors for which Chlamydia does not appear to have the genes for synthesis. For example, genome annotation of Chlamydia includes homologs for all seven genes of the shikimate pathway and predicts that Chlamydia synthesize shikimate and chorismate. Surprisingly, the annotation lacks genes for enzymes that would funnel chorismate into other pathways for synthesis of folate, phenylalanine, tyrosine, tryptophan, and ubiquinone. We are currently attempting to demonstrate that Chlamydia makes chorismate and then will determine how the bacterium inserts this compound into the pathways for which it is a precursor. Similarly, Chlamydia has enzymes that require S-adenosyl methionine (SAM) as a methyl donor but it lacks the metK gene which encodes the enzyme for synthesis of SAM. We have proposed that Chlamydia obtain SAM from the host cytosol via a specific SAM transporter and we have identified a gene from a C. trachomatis library that appears to have SAM transport activity when expressed in E. coli. Finally, we are examining the synthesis/acquisition of lipoic acid by Chlamydia. Lipoic acid is a covalently bound disulfide-containing cofactor required for function of key metabolic pathways in most organisms. These projects may reveal novel pathways that are essential for Chlamydia growth and can therefore provide new targets for drug development. Our long-term goals are to use the genetic tools that we are developing to create defined mutants of Chlamydia to study intracellular metabolism and to understand regulation of the Chlamydia developmental cycle.


Selected Publications

Binet R. and A.T. Maurelli. 2009. Transformation and isolation of allelic exchange mutants of Chlamydia psittaci using recombinant DNA introduced by electroporation. Proc Natl Acad Sci U S A. 106(1):292-7

Zurawski DV, K.L. Mumy, C.S. Faherty, B.A. McCormick, A.T. Maurelli. 2009. Shigella flexneri type III secretion system effectors OspB and OspF target the nucleus to downregulate the host inflammatory response via interactions with retinoblastoma protein. Mol Microbiol. 71(2):350-68.

Faherty C.S. and A.T. Maurelli. 2008. Staying alive: bacterial inhibition of apoptosis during infection. Trends in Microbiology 16(4):173-80. Review.

Zurawski D.V., K.L. Mumy, L. Badea, J.A. Prentice, E.L. Hartland, B.A. McCormick BA, A.T. Maurelli. 2008. NleE/OspZ family of effector proteins is required for PMN transepithelial migration, a characteristic shared by enteropathogenic Escherichia coli and Shigella flexneri infections. Infect Immun. 76(1):369-79.

Binet R. and A.T. Maurelli. 2007. Frequency of Development and Associated Physiological Cost of Azithromycin Resistance in Chlamydia psittaci 6BC and C. trachomatis L2. Antimicrob. Agents Chemother. 51(12):4267-75.

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