Dr. Aimee Shen

Assistant Professor

Sporulation and spore germination in the nosocomial pathogen Clostridium difficile

Mechanisms of spore germination in Clostridium difficile

Clostridium difficile is an emerging pathogen that has been running rampant in hospitals in the past decade as the leading cause of healthcare-associated diarrhea in developed countries. Since 2000, C. difficile infections have risen dramatically in number and severity: there are now 0.5-1 million cases/year in the US alone, with a mortality rate of 3-6%. C. difficile-associated disease is difficult to treat and contain in healthcare settings because it is naturally antibiotic resistant and produces hardy spores.

The spores of C. difficile play a critical role during infection as the major transmissive form, since they are aerotolerant, resist common disinfectants, unaffected by antibiotic treatment, and easily disseminated. As a result, spores are responsible for the high rates of disease recurrence that characterize C. difficile infections. Nevertheless, despite their importance in the pathogenesis of C. difficile, little is known about the basic biology of Clostridium sp. spores.

Research in my lab focuses on understanding how C. difficile spores are assembled during sporulation and disassembled during germination. One challenge to studying C. difficile spores is that less than 25% of the genes encoding spore proteins in the model organism Bacillus subtilis are conserved in the genome of C. difficile. To identify and characterize C. difficile proteins involved in sporulation and spore germination, we are using a combination of genetic, structural, biochemical, transcriptional and proteomic approaches to interrogate these complex developmental processes.

We currently have projects directed at

1. Identifying and characterizing C. difficile spore morphogens
2. Elucidating the molecular mechanisms that regulate cortex hydrolysis during germination
3. Mapping the post-translational changes that occur during germination

Fig. 1. Electron microscopy of C. difficile spores (A) and sporulating cells (B). The arrow in (B) indicates misloalization of the spore coat in a spore assembly mutant.

Fig. 2. Anaerobic chamber for C. difficile work.

BACKGROUND

Dr. Shen received her Ph.D. from Harvard University under the direction of Dr. Darren Higgins, where she studied flagellar gene regulation in the foodborne pathogen Listeria monocytogenes. She did her postdoctoral work in the lab of Dr. Matthew Bogyo at Stanford University, where she used chemical biology to study the regulation of bacterial toxin proteases. She joined the University of Vermont in April 2011 as an Assistant Professor and recently received a Pew Scholars Award in the Biomedical Sciences. Outside the lab, Dr. Shen enjoys running, hiking, climbing, traveling, baking, cooking and chocolate.

LAB MEMBERS

Kelly Fimlaid
        Graduate Student
Kristin Schutz
        Research Technician

SELECTED PUBLICATIONS

Lupardus PJ*, Shen A*, Bogyo M, Garcia KC. Small molecule-induced allosteric activation of the Vibrio cholerae RTX cysteine protease domain. Science. 2008. 322:265-268.

Shen A, Lupardus PJ, Albrow VE, Guzzetta A, Powers JC, Garcia KC, Bogyo, M. Mechanistic and structural insights into the proteolytic activation of the Vibrio cholerae MARTX toxin. Nat Chem Biol. 2009. 5:469-478. PMCID: PMC2783333

Puri AW, Lupardus PJ, Deu E, Albrow VE, Garcia KC, Bogyo M, Shen A. Rational Design of Inhibitors and Activity-Based Probes Targeting Clostridium difficile Virulence Factor TcdB. Chem Biol. 2010. 17:1201-1211.

Shen A, Lupardus PJ, Puri AW, Albrow VE, Gersch MM, Garcia KC, Bogyo M. Defining an Allosteric Circuit in the Cysteine Protease Domain of Clostridium difficile toxins. Nat Struct Mol Biol. 2011. 18:364-371.

Lanis JM, Hightower LD, Shen A, Ballard JD. TcdB from hypervirulent Clostridium difficile exhibits increased efficiency of autoprocessing. Mol. Micrb. 2012. 84:66-76.

Putnam EE, Nock AM, Lawley TD, Shen A. SpoIVA and SipL are Clostridium difficile spore morphogenetic proteins. J Bacteriol. 2013 [Epub ahead of print]

Adams CM, Eckenroth BE, Putnam EE, Doublié S, Shen A. Structural and Functional analyses of the CspB protease required for Clostridium spore germination PLoS Pathogens 2013 In Press