Applications of resonance Raman spectroscopy to algae and bacteria

Qiang Wu, University of Rhode Island

Abstract

Resonance Raman spectroscopy with ultraviolet (UV) excitation has been demonstrated to be a valuable method for the study of biological molecules, including algae and bacteria. ^ Attempts have been made with visible light lasers to excite selectively resonance Raman spectra of algal pigments within the whole cell to see if different classes of algae will give different characteristic Raman spectra. Efforts have been made to determine whether it is possible by Raman spectral means to identify algal species known to produce toxins and to distinguish them from species incapable of producing toxin with visible excitation. Successful attempts have been made to excite selectively domoic acid from cultured toxic algae directly. Enumeration of the cultures of known volume has allowed calculations to be made from spectral data of the amount of domoic acid in each cell. HPLC methods have been used to verify domoic acid concentrations obtained by the UV resonance Raman method. UV resonance Raman spectroscopy has been demonstrated to be a valuable method to detect rapidly and quantify domoic acid in phytoplankton. ^ Resonance Raman spectral cross-sections have been determined for five species of bacteria: E. coli, C. freundii, E. aerogenes, B. subtilis and S. epidermidis. Spectra have been obtained from cultures in the lag, log and stationary growth phase excited in turn by 229, 244, 248 and 251 nm light. A comparison of measured cross-sections with calculated cross-sections has been made for spectra of log-phase E. coli. It is possible to compare measured cross-sections with cross-sections calculated for log-phase E. coli based on the knowledge of known molecular composition. High quality and high signal to noise ratios permit precise quantitative determination of the Raman band intensities in bacteria. Bacterial nucleic acid spectra can be predicted on the basis of nucleic acid base composition. Bacterial Raman spectra excited by 251 nm light reflect nearly exclusively nucleic acid composition. On the average a significant degree of hypochromism observed in E. coli nucleic acid spectra is in a typical range of many nucleic acids. In contrast, the aromatic amino acid protein spectra belonging to the same E. coli cells are strongly enhanced in intensity (show hyperchromism) with 229 nm excitation. Such hyperchromism is attributed to a hydrophobic environment with the proteins. Raman cross sections obtained in this work will allow precise determinations of sensitivity to be predicted in Raman detection. ^

Subject Area

Chemistry, Analytical

Recommended Citation

Qiang Wu, "Applications of resonance Raman spectroscopy to algae and bacteria" (1999). Dissertations and Master's Theses (Campus Access). Paper AAI9955107.
http://digitalcommons.uri.edu/dissertations/AAI9955107

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