Ultraviolet resonance Raman spectroscopic studies of bacteria and bacterial spores

Ebrahim Ghiamati, University of Rhode Island


UV-Resonance Raman spectra (UVRR) of fourteen different types of bacteria which range in DNA G+C content from 32 to 66 percent were examined at laser excitation of 222, 231, 242, and 251 nm. Bacteria were grown on Trypticase soy agar, Trypticase soy broth and Davis minimal media, and harvested at times ranging from 4.5 to 48 hours. Spectral obtained with 222 nm light were nearly growth rate and media independent. Relative intensities of 1556 cm$\sp{-1}$ tryptophan and 1616 cm$\sp{-1}$ tryptophan + tyrosine bands were found to be strongly correlated with bacteria Gram type. In the wavelengths range 222-231 nm aromatic amino acids can be selectively excited, along with some strong nucleic acid peaks with 222 nm excitation. When excited at 242 nm light, only simple spectra of protein tyrosine and tryptophan and various nucleic acids are observed. Large changes in the relative intensities of major nucleic acid peaks have been attributed to very large variations in the RNA content of bacterial cells from culture to culture. The spectral changes are observed whenever differences in growth rates or variations in culture media result in substantial changes in the amount of ribosomal RNA. In spite of very large cultural effects on peak intensities it has been possible to obtain bacterial G+C/A+T ratios from these spectra. Such data have been shown to be growth-time and media independent. With 251 nm excitation, bacterial nucleic acid spectra have been obtained selectively.^ UVRR studies of spores of Bacillus cereus, megaterium, and subtilis showed that the method could be used to selectively and sensitively excite calcium dipicolinate in spores and rapidly identify it, in the presence of large numbers of complex molecules.^ Finally, UVRR spectra of pollens which potentially interfere with rapid detection of bacteria, were studied. Spectra were collected at 222, 231, and 242 nm from whole Sun Glow apricot pollen, Kentucky Blue grass pollen, and Giant Ragweed pollen. All whole pollen spectra were characterized by only one or two strong peaks between 1600-1660 cm$\sp{-1}$. Raman bands due to aromatic amino acids and nucleic acids usually were absent from pollen spectra. (Abstract shortened with permission of author.) ^

Subject Area

Chemistry, General

Recommended Citation

Ebrahim Ghiamati, "Ultraviolet resonance Raman spectroscopic studies of bacteria and bacterial spores" (1990). Dissertations and Master's Theses (Campus Access). Paper AAI9109467.