Biographical Sketch

BS degree in chemistry, August 1977, 
Beloit C
Advisor: William H. Brown, PhD

PhD degree in molecular biology, May 1984
The Pennsylvania State University.
Advisor: Ronald D. Porter, PhD

Postdoctoral Research Fellow, 1984-88, 
Department of Molecular Biology, 
Scripps Clinic and Research Foundation. 
Advisor: Magdalene So, PhD 

Contact information

Department of Microbiology-Immunology
Northwestern University's Feinberg School of Medicine, S213
303 East Chicago Avenue
Chicago , IL 60611

Phone: (312) 503-9788
FAX: (312) 503-1339

Laboratory Members:
Research Faculty: Elizabeth Stohl 
Ph.D. in Cellular and 
Molecular Biology, 1998, 
University of Wisconsin.  
Advisor: Jo Handelsman 
Post-doctoral Fellows: Allen Helm
Ph.D. in Microbiology, 2003,
University of Illinois.
Advisor: Stanley Maloy

Mark Anderson

Ph.D. in Microbiology, 2007

University of Minnesota

Advisor: Sandra K. Armstrong



Adrienne Chen

Ph.D. in Virology, 2007

Harvard University

Advisor: Dr. Frederick Wang

Graduate Students: Melissa Rohrer
B.A. in Biology, 1999,
Carleton College
Paul Schook 
B.A. in Biology, 2004,
Lawrence University
Laty Cahoon 
B.S. in Microbiology, 2003,
Paul Duffin 
B.A. in Biological Chemistry, 2005, Grinnell College



Brian LeCuyer 
B.S. in Biology, 1997, 
University of Illinois 

Research Overview

Our laboratory studies the pathogenesis of Neisseria gonorrhoeae, the causative agent of the sexually transmitted disease gonorrhea. This gram-negative bacterium is an obligate human pathogen that has existed within human populations throughout recorded history. We are using a variety of molecular biological, genetic, cell biological and biochemical techniques to investigate the molecular mechanisms controlling gonococcal infection, define mechanisms and pathways of DNA recombination, replication and repair in this human specific pathogen, study the interactions between gonococci and human cells, tissues and the innate immune system, and determine how the pilus functions to help mediate genetic transfer and pathogenesis. Our goal is to discover new mechanisms important for the continued existence of this microbe in the human population to further our understanding of how infectious agents have evolved to specifically infect humans.

Research Abstract

Antigenic Variation
Our longest running area of interest concerns gonococcal pilus antigenic variation. No documented natural immunity to gonococcal infection exists. This is partly due to the enormous potential N. gonorrhoeae has for antigenic variation of surface proteins. N. gonorrhoeae can express numerous antigenically distinct pilin proteins--the major subunit of the Type IV pilus. This occurs when variant silent pilin sequences, which are found in distinct loci throughout the chromosome, recombine into the singular expression locus. The primary mechanism used by the bacterium to catalyze antigenic variation is gene conversion, or nonreciprocal DNA recombination. How high frequency gene conversion can be mediated between gene copies in several locations on the bacterial chromosome is not well understood. However, we have identified gene products and DNA sequences required for pilin antigenic variation and have developed novel molecular models that explain the molecular characteristics of pilin antigenic variation. We are continuing to discover how these genomic translocations are mediated to test and refine the predictions of these models.

Pilus function
It is well established that the gonococcal Type IV pilus is required for virulence, as it mediates attachment to host cells and tissues, provides force for the specialized movement called twitching motility, and is required for the main means of genetic exchange, DNA transformation. We have shown that the pilus assembly apparatus may act to import DNA into the bacterial cell for genetic transformation and in a mutant background is involved in antibiotic entry into the cell and nutrient transport. We are presently focusing on understanding how the outer membrane secretin protein orchestrates the pilus-dependent processes of adherence, twitching motility, and DNA transformation. We are also investigating how other portions of the pilus cooperate to allow these functions.

Molecular Genetics
Gonococci are gram negative bacteria that have evolved for thousands of years within the human genital tract. This specific environment may provide for unique selection on this species. These cells never are exposed to UV light but are often exposed to reactive oxygen species during infection. We have characterized the peroxide response regulon of N. gonorrhoeae and have interrogated the DNA reapir processes of the organism. Additionally, we have discovered that gonococci are polyploid organisms with more than one complete copy of the chromosome at all stages of growth. Our working model is that gonococci are homozygous diploid and cannot be made to be heterozygous. It is likely the polyploidy is required to allow pilus antigenic variation but this hypothesis remains to be tested. We are investigating how chromosomal replication is initiated and regulated, and how multiple chromosomes are segregated during cell division.

Host cell interactions
Gonococci interact with the genital epithelium and neutrophils during the course of a normal infection. We are examining how pili help mediate the interaction with epithelial cells and whether epithelial cells alter the process of pilin antigenic variation. Neutrophils are sophisticated bacterial killing machines, but gonococci have evolved to live and flourish in their midst. We are examining how gonococci resist oxidative and non-oxidative killing mechanisms that are central to the antibacterial response of neutrophils. We are also exploring whether gonococci modulate neutrophil function.


Recent Publications: 
(Click on icons at left to link to either the full-text PDF or abstract NLM)

*Complete list of Dr. Seifert's publications on Pubmed website

Kline, KA#, Criss, AK#. Wallace, A. &Seifert, HS (2007) Transposon mutagenesis identifies sites upstream of the Neisseria gonorrhoeae pilE gene that modulate pilin antigenic variation. J. Bacteriol. 189: 3462-3470 (#Co-first authors).
Helm, RA, Barnhart, MB, & Seifert HS. (2007) pilQ missense mutations have diverse effects on PilQ multimer formation, piliation, and pilus function in Neisseria gonorrhoeae. J. Bacteriol.189: 3198-3207.
Stohl, E & Seifert HS (2006) Neisseria gonorrhoeae DNA recombination and repair enzymes protect against oxidative damage caused by hydrogen peroxide. J. Bacteriol. 188: 7645-7651.
Criss, AK & Seifert, HS (2006) Gonococci exit apically and basally from polarized epithelial cells and exhibit dynamic changes in type IV piliation. Cell Micro. 8:1430-1443.
Sechman, EV, Kline KA & Seifert, HS (2006) Loss of both Holliday Junction branch migration pathways of Neisseria gonorrhoeae is synthetically lethal in the presence of pilin antigenic variation. Mol Micro. 61:185-193.
Tobiason, D & Seifert, HS (2006) The diplococcus, Neisseria gonorrhoeae, is polyploid. PLoS Biology 4:1069-1078. [Research Highlight: in Nature 441:1030-31, 2006] .
Lusetti, SL, Hobbs, MD, Stohl, EA, Chitteni-Pattu, S, Inman, RB, Seifert, HS, & Cox, MM (2006) The RecF protein antagonizes RecX function via direct interaction. Mol. Cell. 21:41-50.
Stohl, EA, Criss , AK . & Seifert, HS (2005) The transcriptome response of Neisseria gonorrhoeae to hydrogen peroxide reveals genes with previously uncharacterized roles in oxidative damage protection. Mol Microbiol. 58:520-533.
Criss, AK, Kline, KA & Seifert, HS (2005) The frequency and rate of pilin antigenic variation in Neisseria gonorrhoeae. Mol Microbiol. 58:510-519.
Zhao, S#, Tobiason, DM#, Hu M, Seifert, HS, & Nicholas, RA (2005) The penC mutation conferring antibiotic resistance in Neisseria gonorrhoeae arises from a mutation in the PilQ secretin that interferes with multimer assembly and prevents antibiotic influx. Mol. Microbiol. 57:1238-1251. (#co-first authors).
Sechman, EV, Rohrer, MS. & Seifert, HS (2005) A genetic screen identifies genes and sites involved in pilin antigenic variation in Neisseria gonorrhoeae. Mol. Microbiol. 57: 468-483.

Rohrer, M, Lazio, MP & Seifert, HS (2005) A real-time, semi-quantitative RT-PCR assay demonstrates that the pilE sequence dictates the frequency and characteristics of pilin antigenic variation in Neisseria gonorrhoeae. Nucleic Acids Res. 33:3363-3371.

Kline, KA & Seifert, HS (2005) Role of the Rep Helicase gene in Homologous Recombination in Neisseria gonorrhoeae. J. Bacteriol. 187:2903-2907.

Skaar, EP, LeCuyer, B, Lenich, AG., Lazio, MP, Perkins-Balding, D., Seifert, HS & Karls, AC (2005) Analysis of the Piv Recombinase-Related Gene Family of Neisseria gonorrhoeae. J. Bacterial. 187: 1276-1286.

Lusetti, SL, Drees, JC, Stohl, ES, Seifert, HS & Cox, MM (2004) The DinI and RecX proteins are competing modulators of RecA function. J. Biol. Chem. 279:55073-55079.
Chen, C-J, Tobiason, DM, Thomas, CE, Shafer, WW, Seifert, HS, & Sparling, PF (2004) A mutant form of the Neisseria gonorrhoeae pilus secretin protein PilQ allows increased entry of heme and antimicrobial compounds. J. Bacteriol. 186:730-739.
Long, CD, Tobiason, DM, Lazio, MP, Kline, KA & Seifert, HS (2003) Low-Level Pilin Expression Allows for Substantial DNA Transformation Competence in Neisseria gonorrhoeae. Infect. Immun. 71:6279-6291.
Maier B, Potter L, So M, Long, CD, Seifert HS, Sheetz MP. Single pilus motor forces exceed 100 pN. Proc Natl Acad Sci USA . 99:16012-16017.
Stohl EA, Brockman JP, Burkle KL, Morimatsu K, Kowalczykowski SC, & Seifert HS (2003) Escherichia coli RecX inhibits RecA recombinase and coprotease activities in vitro and in vivo. J Biol Chem. 278:2278-85.
Skaar EP, Tobiason DM, Quick J, Judd RC, Weissbach H, Etienne F, Brot N, & Seifert HS (2002) The outer membrane localization of the Neisseria gonorrhoeae MsrA/B is involved in survival against reactive oxygen species. Proc Natl Acad Sci USA 99:10108-10113.

[home] [about the department] [faculty and labs] [contacting us]
graduate programs] [funding]  [building locations] [chicago campus map]
northwestern university] [nu feinberg school of medicine] [disclaimer]

2013 Northwestern University Feinberg School of Medicine Department of Microbiology-Immunology.

All rights reserved. Last updated: February 2013.