International Research Experience for Undergraduates

Kylene Davis

2002 Participant


Prohibitive Conditions for the Growth of Yeast Cultures

Femtosecond laser spectroscopy has recently become an area of high interest. It's applications range from exploration of ultrafast electron dynamics to long lived photoexcitations. To progress into a deeper understanding of ultrafast phenomena it is necessary to know the laser pulse length. As there is no conventional electronics that can measure femtosecond pulses my duties this summer included the design and implementation of an autocorrelator, a device that can indirectly estimate the pulse length.

The setup of an autocorrelator involves splitting a laser beam into two beams of equal intensity and focusing them on a nonlinear medium, in this case a Barium Borate Type I crystal. The result is a second harmonic beam (SH), which is then shot onto a combination photodiode and integrating circuit driver with output to an oscilloscope. The photodiode measures the intensities of the SH beams and the driver circuit integrates the products of the two functions to get the autocorrelation function:

Kylene Lebby Davis is a 19-year-old undergraduate senior with a major in biology and a minor in chemistry from Claflin University located in Orangeburg, South Carolina. She was selected to participate in an undergraduate research internship program (REU) at the University of Florida. Kylene's assigned research field is in Biochemistry. She is a member of the biochemistry research team under the advisement of Dr. Thomas Lyons. Kylene and graduate student, Lisa Regalla are in the process of composing a research grant proposal that will be submitted to The Petroleum Research Fund of the American Chemical Society.

The overall goal of her project is to find conditions which prohibit the growth of yeast cultures. Kylene's research interest is focused on how zinc is taken up by, and regulated in, S. cerevisiae yeast cells.

Previous experiments have proven that the enzyme ZRT 1 acts as a transporter and is involved in the cellular uptake of zinc. Kylene and her research group discovered that once zinc has entered into the yeast cell, it binds to alcohol dehydrogenase VI (Adh6). This binding promotes the conversion of the aldehyde, veratraldehyde (VTA), to an alcohol. It was hypothesized that the metallochaperones, Hsp 26 and Hsp 42 (heat shock proteins that are involved in the folding of other proteins), help shuttle zinc to Adh6.

Kylene conducted an experiment in which she tested zinc deficiency and its effect on VTA toxicity. Yeast strain samples were grown overnight and their optical density measurements were tested every two hours using the spectrometer. Data points were recorded and graphed, resulting in the following: The strains without zinc plus VTA died at a slower rate than the strains with zinc plus VTA, proving that zinc deficiency is effected by VTA. She delivered a Powerpoint presentation before her colleagues, updating them on the status of these preliminary research findings.

This is a diagram of zinc in the cell. It is shown in the nucleus that the Zap1 gene is turned on when the cell is zinc deficient, but the gene turned on by high levels of zinc is unknown.

Davis Diagram

She recently delivered a Powerpoint presentation before her colleagues, updating them on the status of her preliminary research findings.

I just completed a project, in which yeasts strains were plated onto Nutrient agar plates, then placed in a Chelating Synthetic Liquid Media and allowed to shake in the shaking incubator for 24 hours. Using the spectrometer, the Optical Density of each sample was measured, and enough data points were gathered to create growth curves. Just yesterday, in our group meeting I delivered a powerpoint presentation of my research results to the rest of the laboratory members, to keep them up to date on the progress of my research.