Laurie Caslake

Molecular Biology is a set of tools that can be applied to topics ranging from anthropology to zoology. I have chosen to work mostly in the field of environmental molecular microbiology for a variety of reasons that are detailed below. During the 2008-2009 academic year, I am on sabbatical leave and will be a Visiting Scholar at Arizona State University working in the laboratory of Dr. Ferran Garcia-Pichel. There I will be pursuing a new research project on the molecular basis of desiccation resistance in desert crust organisms.

A. Desiccation-Resistance in Desert Crust Microorganisms

While the desert seems to be an inhospitable place, in reality it contains a multitude of diverse microorganisms. Many of these microorganisms live in the crust, the top several mm to cm of soil. In this environment, organisms survive high levels of UV irradiation with very little water. While Dr. Garcia-Pichel’s lab, which I will visit while on leave in 2008-09, is interested in the question, “Who is present in the desert crust?”, I am interested in the question, “How can they live in such an environment?”

Much of what is known about desiccation resistance comes from the Class Deinococci. Deinococcus radiodurans, the most famous member of the Class, was initially isolated from a can of spoiled meat that had been irradiated for sterilization. D. radiodurans has been shown to withstand 500,000 rads of radiation and still maintain the viability of some cells (Mattimore & Battista, 1996. J. Bacteriol. 178: 633-637). PFGE was used to analyze the effect of irradiation on the genome – the results showed the breakdown of the full length genome, approximately 3 Mbp in length, into small fragments estimated to be 50 kbp. Over time, the wild-type irradiated organisms were shown to rebuild a full-length functional, stable, genome from these fragments (Harris et al., 2004. PLoS Biol. 2: e304:1629-1639). Our overriding question is: does the mechanism that allows D. radiodurans to survive irradiation occur in organisms present in the desert crust?

B. Bacterial Pathogens of Fish

A few bacterial species, of the more than 5000 identified, can infect animals and cause disease. My lab became interested in one of these organisms, Flavobacterium columnare, while I was at SUNY-Fredonia. F. columnare causes morbidity and mortality in both warmwater and coldwater fish; early work revealed a difference in the virulence of these organisms. Our initial studies on chondroitin AC lyase, an extracellular enzyme that breaks down chondroitin sulfate, showed a difference in chondroitin AC lyase activity between isolates from coldwater and warmwater fish. The molecular underpinnings of this difference are unknown. We have cloned cslA, the gene for chondroitin AC lyase, from six F. columnare isolates and have sequenced approximately 600 bp of the gene. In fall 2009, I will be looking for a student to help sequence and analyze the rest of this gene. Our long-term goal is to understand the molecular basis of the virulence differences.

C. The Onondaga Lake (Syracuse NY) Ecosystem

Onondaga Lake, with its abundant brine deposits, was the site of a chlor-alkali facility in the early 1900’s, which produced chlorine gas and sodium hydroxide. This process used a floating mercury electrode as the cathode and as a solvent for sodium. Each electrolytic cell is estimated to have contained approximately four tons of mercury and there were dozens of electrolytic cells in operation (Chemistry in Context, 1994). Unfortunately, the chlor-alkali process resulted in the release of an estimated 76,000 kg of mercury into Onondaga Lake. Below is a brief description of the projects in which my research students have been engaged.

Molecular analysis of mercury-resistant microorganisms. Water and sediment samples were collected from several sites in Onondaga Lake. Mercury-resistant organisms were quantified through growth on plate count agar in the presence of 100 µM HgCl2. We detected an uneven distribution of mercury-resistant organisms in Onondaga Lake with the highest percentage in samples from Ley Creek.

The mer operon contains several accessory genes such as merB, encoding organomercurial lyase. The presence of MerB allows the organism to cleave the carbon-metal bond found in methyl- and dimethyl-mercury, producing mercuric ion, Hg2+, which is then reduced by MerA to Hg0. We analyzed the mercury-resistant population for the presence of MerB by growth in the presence of 25 µM phenylmercuric acetate and the presence of merB by PCR and Southern hybridization.

RFLP analysis of merA from mercury-resistant microorganisms. Using primers designed to conserved regions of merA, encoding mercuric reductase, we have found eight different NciI restriction fragment length polymorphism patterns in the mercury resistant microorganisms from Onondaga Lake. Six of these RFLP patterns were previously identified in fecal flora from primates with dental amalgams (Liebert et al., 1997, Appl. Environ. Microbiol. 63:1066-1076). The two unique merA RFLPs are being analyzed for sequence variations leading to the new NciI digest patterns.

Antibiotic resistance in mercury-resistant and susceptible microorganisms. An early observation in the studies of antibiotic resistance was that 65% of people tested carried multiple antibiotic-resistant bacteria (Levy et al., 1988, Antimicrob. Agents Chemother. 32:1801-1806). Studies show a genetic linkage between antibiotic resistance and heavy metal resistance, including mercury. Initial studies of our population of mercury-resistant organisms revealed several isolates with multiple antibiotic resistances. We have screened our mercury-resistant organisms for antibiotic resistance, the presence of a class 1 integron, and the capacity for transfer via conjugation.

Analysis of bacteria associated with aquatic macrophytes. Mercury is toxic to aquatic plants and animals, yet the macrophytes in Onondaga Lake are healthy and lack signs of mercury toxicity. Even after bringing macrophytes into the laboratory and exposing them to mercury through the sediments for up to six weeks, they remained healthy. This is in contrast with macrophytes from Pennsylvania’s Lake Nockamixon, which showed classic signs of metal toxicity. We undertook this study to investigate the mechanism by which macrophytes contend with mercury contamination.

D. Applied Microbiology.

I have contributed to several research projects initiated by faculty in Lafayette’s Department of Chemistry and in our Division of Engineering.

Solar Irradiation to Reduce Microbial Counts in Contaminated Water (with the Chemical Engineering Department). We used a fabricated solar disinfection unit to reduce the bacterial load in river water and partially processed water from two wastewater treatment plants. The unit reduced the bacterial load by more than 99.99% in highly contaminated water samples in less than 30 min in midday sunlight.

Stabilizing Sandy Soils With the Addition of Microbes (with the Civil & Environmental Engineering Department). Seismic loads result in an increase in the porewater pressure. In loose, sandy soils, this increase in pressure results in liquefaction of the soil. We are pursuing the use of bacteria to increase the strength of saturated sand, with the goal of possibly using this technique to reduce shifting of sandy sediments during earthquakes.

Chemical Reduction of Perchlorate by Microbes (with the Chemistry Department). Perchlorate has been identified as a significant water contaminant throughout the US. Some bacteria – predominantly in the Proteobacteria group – are capable of reducing perchlorate in the absence of oxygen. Our goal is to develop a combined process using (i) ion exchange to concentrate the perchlorate from groundwater, and (ii) perchlorate reducers to chemically reduce the perchlorate to chloride, an innocuous ion.

Student research publications

Many student-driven research projects lead to a presentation at a regional or national meeting or perhaps a publication in a scientific journal. These achievements are large feathers in their professional caps. Listed below are select recent abstracts and full publications by Lafayette students who have collaborated with me in research.

Abstracts with undergraduate research students (denoted by *):

  • Hecht*, B., Kohen*, K., Tavakoli, J., Kney, A.D., Mylon, S.E., and Caslake, L.F. Development of a perchlorate remediation process using ion exchange and microbial reduction. Poster presentation at the Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, 2006.
  • Jenkins*, J., Dimick*, P, Tavakoli, J., Kney, A.D., Mylon, S.E. and Caslake, L.F. Development of a perchlorate removal process using polymeric ligand exchange. Poster presentation at the Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, 2006.
  • Walsh*, C.E. and Caslake, L.F. Conjugal transfer of antibiotic resistance from environmental isolates. Podium presentation at the Annual Meeting of the Pennsylvania Academy of Sciences, 2006. Grantville, PA.
  • Banagan*, B.L., Wertheim*, B.M., Roth, M.J.S., and Caslake, L.F. A box model to test sand strength after the addition of bacteria. (Abstract accepted). Poster presentation at the 105th General Meeting of the American Society for Microbiology, 2005, Atlanta GA.
  • Jenkins*, J., Hecht*, B., Kohen*, K., Dimick*, P., Tavakoli, J., Kney, A.D., Mylon, S. and Caslake, L.F. Development of a perchlorate remediation process using ion exchange and microbial reduction. Poster presentation at the Regional Microbiology Educators Network Symposium. Swarthmore College, Swarthmore, PA, 2005.
  • Fitzpatrick*, C.M., L. Williams* and L.F. Caslake. Analysis of Onondaga Lake isolates for broad-spectrum mercury resistance. Poster presentation at The 104th General Meeting of the American Society for Microbiology, 2004. New Orleans, LA.
  • Wertheim*, B.M., B.L. Banagan*, M.S. Roth and L.F. Caslake. Exploratory research in microbial remediation of liquefiable soils. Poster presentation at the Regional Microbiology Educators Network Symposium, 2004. Swarthmore College, Swarthmore, PA.
  • Schneck*, J.L. and L.F. Caslake. Genetic variability of Flavobacterium columnare. Podium presentation at the annual meeting of the Pennsylvania Academy of Sciences, 2004. Monroeville, PA.
  • Giordano*, S.M. and L.F. Caslake. Class 1 integrons present in both mercury-resistant and mercury-sensitive isolates from Onondaga Lake. Poster presentation at the St. Joseph University Sigma Xi Student Research Symposium, 2004. Philadelphia, PA.
  • Schrack*, K. and L.F. Caslake. Microbial antibiotic resistance from a mercury-impacted lake. Poster presentation at The 103th General Meeting of the American Society for Microbiology, 2003. Washington D.C.
  • Shaya*, M. and L.F. Caslake. Analysis of chondroitin AC lyase from Flavobacterium columnare. Podium presentation at the annual meeting of the Pennsylvania Academy of Sciences, 2003. Grantville, PA.
  • Williams*, L. and L.F. Caslake. Analysis of bacterial isolates from water samples from Onondaga Lake for the presence of broad-spectrum mercury resistance. Podium presentation at the Pennsylvania Academy of Sciences, 2003. Grantville, PA.
  • Guinan*, M.C. and L.F. Caslake. RFLP analysis of merA in mercury resistant organisms yields new variants. Poster presentation at the Pennsylvania Academy of Sciences, 2003. Grantville, PA.
  • Schrack*, K. and L.F. Caslake. Analysis of class 1 integron in multiple antibiotic resistant environmental isolates. Podium presentation at the Pennsylvania Academy of Sciences, 2003. Grantville, PA.

Full Publications:

  • Schneck*, J. L. & L. F. Caslake. 2006. Genetic diversity of Flavobacterium columnare isolated from warmwater and coldwater fishes. Journal of Fish Diseases 29: 2465-248.
  • Caslake, L.F., S.S. Harris*, C. Williams*, and N.M. Waters. 2006. Mercury-resistant bacteria associated with macrophytes from a polluted lake. Water, Air & Soil Pollution 174: 93-105.
  • Caslake, L.F., D.J. Connolly*, V. Menon*, C.M. Duncanson*, R. Rojas and J. Tavakoli. 2004. Disinfection of contaminated water using solar irradiation. Applied and Environmental Microbiology, 70:1145-1151. Results from field-testing in Peru were included in this publication.

My research students at Lafayette College and their current positions (when known). If your name is in this list and would like to update your information, click here).

  • Christopher Cosgrove (Biology ’10)
  • Brian Kilmartin (Biology ’09)
  • Leah Leinbach (Biology ’08) Starting as a lab technician at University of Pennsylvania.
  • Evan Cohen (Biochemistry ’08)
  • Nathan Parker (Biology ’08) Starting at Teach for America, summer 2008.
  • Brad Wertheim (Biochemistry ’07) Enrolled at Harvard Univ. School of Medicine.
  • Colleen Walsh (Biology ’06) Enrolled at Wake Forest Univ. School of Medicine.
  • Stephanie Giordano (Neuroscience ’05). Currently attending optometry school.
  • Gillian Breslin (Biology ’05). Enrolled at New York Medical College.
  • Nicole Prestiano (Biology ’05). Currently applying to Masters in Public Health programs.
  • Blaire Banagan (Civil and Environmental Engineering ’05) Honors thesis title: Increasing the strength of sandy soils through the addition of bacteria.
  • Tim Byrnes (Biology ’05) Attending medical school in Philadelphia.
  • Jessica Schneck (Biochemistry ’04). Honors thesis title: Molecular analysis of Flavobacterium columnare isolated from diseased fish. Currently a lab technician at Thomas Jefferson University.
  • Colleen Fitzpatrick (Biology ’04). Currently a lab technician at Thomas Jefferson University.
  • Katie Schrack (Neuroscience ’03). Honors thesis title: Identification of class 1 integrons in aquatic environmental isolates from Onondaga Lake. Supported by an Undergraduate Research Fellowship from the American Society for Microbiology, summer 2002. Currently a medical student at Jefferson Medical School.
  • Melissa Shaya (Biology ’03). Honors thesis title: Analysis of chondroitin AC lyase from Flavobacterium columnare. Attended Philadelphia College of Osteopathic Medicine.
  • Lee Williams (Biology ’03). Honors thesis title: Analysis of bacterial isolates from water samples from Onondaga Lake for the presence of broad-spectrum mercury resistance. Attended New York College of Osteopathic Medicine.
  • Cheryl Christianson (Biology ’03). Currently a lab technician at Lewis-Sigler Institute for Integrative Genomics at Princeton University.
  • Ashley Palmer (Biology ’03). Honors thesis title: Differential gene expression in response to nitrogen limitation in Escherichia coli by microarray analysis. Currently a research technician at Progenics Pharmaceuticals at New York Presbyterian Hospital.
  • Mary Cate Guinan (Biology ’03)
  • Jaclyn Wertheimer (Biology ’02). Attended dental school at University of Pennsylvania.
  • Vilas Menon (Chemical Engineering ’02). Entered graduate school at Northwestern Univ.
  • Catriona Duncanson (Chemical Engineering ’02)
  • Kristen Pompizzi (Biochemistry ’01). Attended Thomas Jefferson Univ. Jefferson Medical College.
  • Rhonda Aboulafia (Biology ’01). Attended SUNY Upstate Medical University.
  • Joanne Klimas (Biology ’01). Pursued graduate studies at University of Pennsylvania.
  • Maurienne Will (Biology ’00).