Marcia R. Lee

Associate Professor of Microbiology

Office: 58 Pearson Hall
Phone: (513) 529-5425


D.V.M., University of Minnesota, 1980

Research Interests

We are exploring differential effects of antifungal agents upon conidial and hyphal morphologic forms of the increasingly frequent fungal opportunists Aspergillus fumigatus, Fusarium oxysporum and Candida albicans. Our goal is to identify antifungal agents, including natural antifungal compounds, which inhibit growth of the in vivo fungal hyphal forms and/or inhibit germination of infective fungal conidia, an initial step occurring prior to fungal invasion of host tissue. Our experiments utilize classical microtiter and cultural methods together with flow cytometry and fluorescent microscopy.

Furthermore, we are studying ice nucleating active (INA) fungi and bacteria. Small volumes of pure water remain liquid, i.e. do not freeze, when cooled to temperatures as low as approximately -40°C unless a nucleating substance is present. The most efficient and most common known nucleators, found in leaves, in clouds, oceans, and animals, are INA bacteria and fungi. These microbes can regulate the freeze-susceptibility of insects, most of which are freeze-intolerant. In the winter many of these insects survive by increasing their capacity to supercool, and thus, avoid the lethal effects of internal ice formation. Increases in supercooling capacity require the removal or inactivation of heterogeneous ice-nucleating catalysts. Although several lines of evidence suggest that ice nucleation begins in the gut, the precise nature of the ice nucleating agent regulating supercooling in freeze-intolerant insects is not clearly established. Our laboratory in recent years provided the first evidence that the ingestion or cuticular application of INA bacteria significantly decreases the supercooling capacity and, as a result, reduces the cold tolerance of a wide variety of insects. We also established that INA bacteria are normal flora in the gut of insects. The selected insect host for our research, the Colorado potato beetle, is freeze-intolerant, and is the primary potato pest in North America, appearing to be an excellent candidate for control using INA microorganisms. Ultimately, we hope to develop probes to detect the presence of INA genotypes in and on insects to accompany cultural, fluorescent, and nucleation studies which detect the presence of the INA positive phenotype. We seek to determine the potential for use of INA bacteria and fungi as biological control agents for insect pests, initially the Colorado potato beetle.

Selected Publications

  • Humphreys, T.L., Castrillo, L.A., and M.R. Lee. 2001. Sensitivity of partially purified ice nucleation activity ofFusarium acuminatum SRSF 615. Current Microbiology 42:330-338.
  • Castrillo, L.A., R.E. Lee, J.A. Wyman, M.R. Lee, and S.T. Rutherford. 2001. Field persistence of ice-nucleating bacteria in overwintering Colorado potato beetles. Biological Control 21:11-18.
  • Castrillo, L.A., Lee, R.E., M.R. Lee and J.A. Wyman. 2000. Long-term retention of ice-nucleating activePseudomonas fluorescens by overwintering Colorado potato beetles. CryoLetters 21:5-12.
  • Fairbank, K.L., Gutierrez, K.R., Karipides, S., M.M. Cowan and M.R. Lee (presenter). Rapid susceptibility testing of filamentous fungi. 39th Annual Meeting of the Interscience Conference of Antimicrobial Agents and Chemotherapy (ICAAC), San Francisco, CA. October 3, 1999. Abstract.
  • Lee, M.R., R.E. Lee, Strong, J.M., S.R. Minges and J.A. Mugnano. 1998. Reduction of insect cold-hardiness using ice-nucleating active fungi and surfactants. Entomologia Experimentalis et Applicata 89:103-19.