Interactions of Selenium Species with Living Bacterial Cells - A Fourier Transform Infrared Spectroscopy Approach

One area of astrobiology is devoted to duplicating conditions that exist on remote planets and moons (like Mars and Europa) on Earth, and studying the life that survives there. A variety of bacteria can thrive in inhospitable environments. An essential nutrient for life at low concentration can be a deadly poison at higher concentration. Fourier-transform infrared (FT-IR) spectroscopy is employed in this research for the determination of selenium species by using living bacterial cells. The extraction medium consists of an E. coli strain (K-12) cultivated in a culture medium based on glucose contaminated with selenium species. First, equilibrium between the analyte in the solution and the retention medium is established, and then interactions of selenium species with living bacterial cells are characterized by FTIR spectroscopy of whole cells. The presence of the toxicants at various concentrations in the culture medium has an affect on the FT-IR spectra and the concentration of the selenium species is determined directly in the biomass by FT-IR spectroscopy. The relative intensities of several peaks, which vary as a function of the selenium species concentration, are used as the analytical signal. The best detection limits for the organoseleno compounds at their optimum extraction times are of 0.5-1.5 ng ml-1 for selenomethionine (Se-Met) and 1.0-2.6 ng ml-1 for selenoethionine (Se-Et) depending on the intensity ratio used. The relative standard deviations of the retention/determination process are about 5.0% for all the selenium species tested.