In situ micro X-ray absorption near edge structure study of microbiologically reduced selenite (SeO 32−)

Abstract

The possibility exists that life originated from high-pressure, high-temperature environments fueled by the reduction of metal ions. These environments or their modern equivalent cannot be studied by standard microbiological techniques, but, metal reduction and oxidation kinetics may be accessible to X-ray analyses. We have evaluated the compatibility, the sensitivity and the efficiency of μX-ray absorption near edge structure (μXANES) and μX-ray fluorescence (μXRF) to study the kinetics of selenite reduction by prokaryotes under controlled pressure and temperature using a dedicated diamond anvil cell. These tests were performed in quartz capillaries, but the experimental set up was designed so as to accommodate the diamond anvil cell. Using μXRF coupled with μXANES, we show that we can detect and quantify Se species in solution from as low as 2 ppm. Lower quantification levels could be readily obtained by increasing counting time or incident flux and changing detectors. The chemical composition of mixtures of different selenium species has been directly determined by a combination of individual μXANES spectra made from standard solutions. The sensitivity of this method is sufficiently high to allow the study of the speciation of selenium in solution in situ and in vivo in the diamond anvil cell under controlled pressure and temperature.