BS degree in chemistry, August
Advisor: William H. Brown, PhD
PhD degree in
molecular biology, May 1984
The Pennsylvania State University.
Advisor: Ronald D. Porter, PhD
Postdoctoral Research Fellow,
Department of Molecular Biology,
Scripps Clinic and Research Foundation.
Advisor: Magdalene So, PhD
Northwestern University's Feinberg School of Medicine, S213
303 East Chicago Avenue
Phone: (312) 503-9788
FAX: (312) 503-1339
Ph.D. in Cellular and
Molecular Biology, 1998,
University of Wisconsin.
Advisor: Jo Handelsman
Ph.D. in Microbiology, 2003,
University of Illinois.
Advisor: Stanley Maloy
Ph.D. in Microbiology, 2007
University of Minnesota
Advisor: Sandra K. Armstrong
Ph.D. in Virology, 2007
Advisor: Dr. Frederick Wang
B.A. in Biology, 1999,
B.A. in Biology, 2004,
B.S. in Microbiology, 2003,
Biological Chemistry, 2005, Grinnell College
B.S. in Biology, 1997,
University of Illinois
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
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.
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.
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.
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
(Click on icons at
left to link to either the full-text PDF or abstract NLM)
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.
Helm, RA, Barnhart, MB, &
missense mutations have diverse effects on PilQ multimer formation,
piliation, and pilus function in
Stohl, E & Seifert
DNA recombination and repair enzymes protect against oxidative damage
caused by hydrogen peroxide.
& Seifert, HS (2006)
Gonococci exit apically and basally from
polarized epithelial cells and exhibit dynamic changes in type IV
piliation. Cell Micro.
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
D & Seifert, HS
(2006) The diplococcus, Neisseria
gonorrhoeae, is polyploid. PLoS
[Research Highlight: in Nature
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.
. & Seifert, HS (2005)
The transcriptome response of
Neisseria gonorrhoeae to hydrogen peroxide reveals genes with
previously uncharacterized roles in oxidative damage protection. Mol
AK, Kline, KA & Seifert, HS (2005)
The frequency and rate of pilin antigenic variation in Neisseria
gonorrhoeae. Mol Microbiol.Ê
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.
EV, Rohrer, MS. & Seifert, HS
(2005) A genetic screen identifies genes and sites involved in pilin
antigenic variation in Neisseria gonorrhoeae. Mol. Microbiol.
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.
KA & Seifert, HS
(2005) Role of the Rep Helicase gene in
Homologous Recombination in
Neisseria gonorrhoeae. J.
EP, LeCuyer, B, Lenich,
AG., Lazio, MP, Perkins-Balding, D., Seifert, HS & Karls,
Analysis of the Piv Recombinase-Related
Gene Family of Neisseria
Bacterial. 187: 1276-1286.
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.
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.
||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.
B, Potter L, So M, Long, CD, Seifert HS, Sheetz MP.
Single pilus motor forces exceed 100 pN.
Proc Natl Acad
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
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