Frank Gherardini, Ph.D.

Chief, Gene Regulation Section
Senior Investigator

Dr. Gherardini received his doctorate in 1987 from the University of Illinois, studying enzymes involved in the utilization of galactomannans by Bacteroides ovatus. In 2000, Dr. Gherardini joined NIAID's Rocky Mountain Laboratories, where he is currently a senior investigator in the Laboratory of Zoonotic Pathogens.

Description of Research Program

Borrelia Projects: This research focuses on the physiology, biochemistry, gene regulation, and pathogenesis of Borrelia burgdorferi, the causative agent of Lyme disease in humans. B. burgdorferi faces several environmental and immunological challenges during its infective cycle and must alter (regulate) gene expression to successfully adapt to these conditions.

Analysis of the B. burgdorferi genome sequence has revealed that there are very few known regulatory proteins in this bacterium.Conspicuously absent are global regulatory proteins such as CRP, LexA, Fnr, IHF, OxyR, Lrp, and the sigma factors involved in the heat shock response, Ó 32 and Ó 24.

During the transmission of Lyme disease, reactive oxygen (ROS) and reactive nitrogen (NOS) present a challenge to the survival of B. burgdorferi. As the bacteria move from the midgut to the feeding site, they encounter a dramatic increase in ROS and respond by increasing the expression of key protective enzymes (NapA, NpX, TrxR, and Trx).

This suggests that, compared to other well-characterized pathogenic bacterial systems, the global regulatory systems operating in B. burgdorferi are relatively simple. Clearly, these systems are required for B. burgdorferi to adapt as it encounters very different environments during transfer from an animal reservoir to the tick and then to a human host.

Our research efforts have focused on three important regulatory proteins: 1) BosR, a Zn-dependent transcriptional activator that regulates key antioxidant enzymes; 2) Ø 54, an alternate sigma factor that also regulates certain parts of the oxidative stress response and regulates the osmotic stress response; and 3) Ø S which controls the stationary phase of growth and the expression of genes that are critical to the pathogenesis of Lyme disease.

Burkholderia Projects: Burkholderia pseudomallei, the etiological agent of melioidosis, is a Gram-negative, facultatively anaerobic, motile bacillus that is responsible for a broad spectrum of illnesses observed in both humans and animals.

B. pseudomallei (designated by arrow) surviving inside a human macrophage.

While epidemiological surveys have demonstrated that B. pseudomallei is endemic to regions that typically border the equator, the incidence of disease is particularly high in Southeast Asia and Northern Australia. In northeastern Thailand alone, an estimated 20% of community-acquired septicaemias and approximately 40% of deaths due to complications associated with bacterial sepsis can be attributed to this organism. The manifestations of melioidosis are commonly represented by acute, sub-acute and chronic illnesses, with the clinical manifestations often being mistaken for malaria, plague, pneumonia, and miliary tuberculosis. Infections are typically acquired via inhalation or aspiration, ingestion, or via the direct contact of damaged surface tissues with contaminated waters or soils.

Burkholderia mallei, the etiological agent of glanders, is a Gram-negative bacterium that is responsible for disease in donkeys, mules, horses, and occasionally humans. Unlike the environmental saprophyte B. pseudomallei, however, B. mallei does not persist in nature outside of its soliped hosts. While B. mallei and B. pseudomallei are genotypically similar, significant phenotypic differences do exist between the two pathogenic species. Although glanders is one of the oldest diseases known to man, relatively little is known about the pathogenesis of disease caused by B. mallei. This phenomenon is due primarily to the lack of disease in North America, along with the fact that B. mallei can be a particularly dangerous organism to study even in a controlled laboratory environment.

B. pseudomallei is known to resist the bactericidal activity of both reactive oxygen and nitrogen intermediates as well as to survive and multiply within several mouse and human macrophage cell lines (see electronmicrograph). In order to identify genetic loci associated with these virulence phenotypes, specifically those genes that are up- or down-regulated in an intracellular environment, we use a standard macrophage uptake assay, recover the intracellular bacteria, and isolate bacterial mRNA to probe DNA micro-arrays. The data sets obtained from these studies are used to identify genes required for intracellular survival. Genes of interest are disrupted by allelic exchange and their function(s) are defined using both in vivo model systems (mouse macrophage invasion, infectivity in hamsters, etc.).

Major Areas of Research

• Borrelia burgdorferi
• Treponema pallidum
• Burkerholderia mallei
• Burkerholderia pseudomallei

Research Group Members

Back row: Kevin Lawrence, M.S.; John Warawa, Ph.D.; Paul Brett, Ph.D.; Mary Burtnick, Ph.D.; Su Hua, Ph.D.;
Front row: Alison Moran; Julie Boylan, Ph.D.; Frank Gherardini, Ph.D.

Selected Publications

(View list in PubMed.)

Brett PJ, Burtnick MN, Su H, Nair V, Gherardini FC. iNOS activity is critical for the clearance of Burkholderia mallei from infected RAW 264.7 murine macrophages. Cell Microbiol. 2008 Feb;10(2):487-98.

Burtnick MN, Downey JS, Brett PJ, Boylan JA, Frye JG, Hoover TR, Gherardini FC. Insights into the complex regulation of rpoS in Borrelia burgdorferi. Mol Microbiol. 2007 Jul;65(2):277-93.

Boylan JA, Hummel CS, Benoit S, Garcia-Lara J, Treglown-Downey J, Crane EJ3rd, Gherardini FC. Borrelia burgdorferi bb0728 encodes a coenzyme A disulphide reductase whose function suggests a role in intracellular redox and the oxidative stress response. Mol Microbiol. 2006 Jan;59(2):475-86.

Fisher MA, Grimm D, Henion AK, Elias AF, Stewart PE, Rosa PA, Gherardini FC. Borrelia burgdorferi sigma54 is required for mammalian infection and vector transmission but not for tick colonization. Proc Natl Acad Sci U S A. 2005 Apr 5;102(14):5162-7.

Boylan JA, Posey JE, Gherardini FC. Borrelia oxidative stress response regulator, BosR: a distinctive Zn-dependent transcriptional activator. Proc Natl Acad Sci U S A. 2003 Sep 30;100(20):11684-9.

Posey JE, Gherardini FC. Lack of a role for iron in the Lyme disease pathogen. Science. 2000 Jun 2;288(5471):1651-3.

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