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Dr. Leonardo's Research Interests


Microbial Iron Reduction by Shewanella species

Microbial Fe(III)-reduction has only recently been recognized and yet is now considered a predominant form of microbial respiration. Geological studies of Precambrian Banded Iron Formations (BIFs) have suggested that the oxidation of organic matter coupled to the reduction of the ferric (Fe(III)) iron was one of the first significant biological processes for the complete oxidation of organic carbon back to carbon dioxide. The broad taxonomic diversity of the few known Fe(III)-reducing bacteria supports the proposal that this form of metabolism may have evolved early in the Earth's history. In contemporary environments microbial reduction of Fe(III) remains one of the most important chemical changes that occurs in the development of modern anaerobic soils and sediments, and plays an important role in the cycling of trace metals and nutrients in anaerobic aquatic environments.

My research interests are in the study of microbial Fe(III) reduction in soils and sediments by the metal-reducing bacteria Shewanella. This ubiquitous aquatic bacteria can use iron and a variety of other metals as an electron acceptor under anaerobic conditions. This ability makes Shewanella species potential major players in bioremediation of a variety of environments. In addition, when attached to a solid surface, Shewanella produces a layer of hydrated polymers called extracellular polymeric substances (EPS). This creates microenvironments which allows for anaerobic growth even in the presence of oxygen. The can lead to biofouling and biocorrosion of industrial pipes. We are looking at what happens to Shewanella's ability to perform metal reduction when it is unable to produce EPS.

Studies of Tube worm normal flora

Studies of biocement production by the tube worms Pectinaria gouldii and Phragmatopoma lapidosa are being conducted by Dr. Maria Dean in the Coe Department of Chemistry. During these studies, it was noticed on scanning electron micrographs that there were microorganisms living on the surface of these two species of tube worms. We have been using classic microbiological and molecular techniques to classify and identify these worm-associated microorganisms. Future studies will look at the purpose of this relationship between the worms and their flora.

Development of antibacterial glass

In collaboration with Dr. Mario Affatigato in the Coe Department of Physics, we have been working to develop glass that resists the colonization and growth of potentially pathogenic microorganisms. Studies have focused on synthesizing glass of different components that, when exposed to aqueous environments, inhibit the growth of E. coli, Salmonella, and other potentially pathogenic microorganisms such as Staphylococcus aureus.

Studies of the Squid Symbiont Shewanella pealeana

As part of the 1996 Microbial Diversity Course associated with the Marine Biological Laboratories at Woods Hole Oceanographic Institute, analysis of the microbial community of the accessory nidamental gland (ANG) of the Atlantic squid Loligo pealei was begun.  The ANG is associated with the reproductive system of the squid, but its function is unclear. When the squid is sexually mature, the ANG is teaming with a diverse community of microorganisms.  It appears that these microorganisms are secreted into the egg capsule while the squid is laying her eggs.  Preliminary studies have shown that these microorganisms seem to provide some protection to the developing eggs from marine pathogens by producing anti-microbial agents.  Shewanella pealeana was one of the members of this community.  I am interested in studying the physiology of this symbiotic microorganism.  Studies of how S. pealeana survives the environmental changes of living within the squid and the free ocean, how it colonizes the ANG, and its metabolism are in the works.

Ethanol Production in Escherichia coli

I am interested in elucidating the way in which the synthesis of ethanol and related fermentation products are regulated in the facultative anaerobe Escherichia coli. In particular, the expression of the adhE gene, encoding the multifunctional alcohol dehydrogenase (AdhE). AdhE, the key enzyme in fermentation, is being studied by means of bacterial genetics and molecular biology. The adhR gene, encoding a regulator that mediates the response of adhE to the NADH level, has been shown to have NADH-dependent binding to the adhE upstream region by gel retardation. In addition to AdhR/NADH, the expression of the adhE gene also responds to molybdenum levels. The effects on expression of adhE under such conditions are being analyzed. The results should contribute to our fundamental understanding of the genetic regulation of anaerobic growth.


(2000-01) Julie Boerkel-Hall, Ph.D. in Genetics-Postdoctoral Fellow @ National Institute of Environmental Health Sciences

(2000-01) Anne Rizza, M.A. in Forensic Science

(2000-02) Christopher Malozzi, D.O. - Resident @ University of South Alabama Medical Center

(2001-02) Timothy Houser, D.D.S. - Private Practice

(2002-03) Courtney Knauss, M.D. -Resident @ Eastern Virginia Medical Center

(2002-03) Jordan Bicher, DPT

(2004) Desirae Leipply, Ph.D. student @ Johns Hopkins University in biophysics

(2005) Bradley Melhus, D.D.S. -Private practice

(2005) Lynette Wickman, Pharmacy student @ University of Iowa School of Pharmacy

(2005-06, 2008) Patricia Davison, Ph.D. student in Cellular and Molecular Biology @The Ohio State University

(2005-06) Brady Miller, MPH -ASPH/CDC Fellow @ Centers for Disease Control and Prevention

(2006, 2008) Laura Steele, Ph.D. student @ the University of Illinois-Urbana/ Champaign in entomology

(2006) Bailey Clark, graduates in 2010

(2007) Jobin Abraham, MPH - Operations Manager @ Bayer HealthCare

(2007) Alex Michaud, Ph.D. student in the IGERT program @ Montana State University in microbial ecology

(2007) Clarissa Thomas, graduates in 2011

(2008-09) Anni Arcand, graduates in 2011

(2009) Reshica Baral, graduates in 2011

(2009) Kailin Breitbach, graduates in 2011

(2009) Cassie Morgan, graduates in 2011

(2009) Peter Miller, graduates in 2013