Monitoring of cobalt(II) uptake and transformation in cells of the plant-associated soil bacterium Azospirillum brasilense using emission Mössbauer spectroscopy

Abstract

Interaction of cobalt(II) at micromolar concentrations with live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (strain Sp245) and further transformations of the metal cation were monitored using 57Co emission Mössbauer spectroscopy (EMS). Cell suspensions of the bacterial culture (2.4 x 10(8) cells ml(-1)) were doped with radioactive 57CoCl2 (1 mCi; final concentration 2 x 10(-6) M 57Co2+), kept under physiological conditions for various periods of time (from 2 min up to 1 hour) and then rapidly frozen in liquid nitrogen. Analysis of emission Mössbauer spectra of the frozen aqueous suspensions of the bacterial cell samples shows that the primary absorption of cobalt(II) at micromolar concentrations by the bacterial cells is rapid and virtually complete, giving at least two major forms of cobalt(II) species bound to the cells. Within an hour, the metal is involved in further metabolic transformations reflected by changes occurring in the spectra. The Mössbauer parameters calculated from the EMS data by statistical treatment were different for suspensions of live and dead (thermally killed) bacterial cells that had been in contact with 57Co2+ for 1 h, as well as for the cell-free culture medium containing the same concentration of 57Co2+. Chemical after-effects of the nuclear transition (57Co --> 5 7Fe), which provide additional information on the chemical environment of metal ions, are also considered. The data presented demonstrate that EMS is a valuable tool for monitoring the chemical state of cobalt species in biological matter providing information at the atomic level in the course of its uptake and/or metabolic transformations.

Effects of trapped electrons on the line shape in emission Mössbauer spectra

“…The 119m Sncontaining system (sample 4) was represented by ethanolic solutions of 119m SnCl 2 with different concentrations of CrCl 2 (added as an electron scavenger) rapidly frozen in liquid nitrogen. Other details of emission Mössbauer measurements and statistical treatment of the experimental data were described elsewhere [8][9][10][11].…”

Application of 57Co emission Mössbauer spectroscopy to studying biocomplexes in frozen solutions

“…The absorber (K 4 [ 57 Fe(CN) 6 ] 3H 2 O) was attached to a vibrator in the γ-ray beam path (sampleabsorber-detector). Other details of EMS measurements and statistical treatment of emission spectra were described elsewhere [7,12]. All isomer shift values are presented relative to α-Fe at ambient temperature (converted into a form compatible with that of conventional absorption 57 Fe Mössbauer measurements, positive with regard to α-Fe).…”

Advanced nuclear analytical techniques for metalloproteomics

“…[89][90][91][92][93] The samples subjected to Mo¨ssbauer spectroscopy are generally purified proteins in solid state or in frozen solution. 94 Some tissue specimens have also been used for an in situ Mo¨ssbauer spectroscopy survey to elucidate the relationship of iron with certain diseases. [86][87][88] Proper model compounds with characterized structures can be used to demonstrate the relationship existing between the coordination field and Mo¨ssbauer spectroscopic properties, which is beneficial to detect the ''small'' changes in biomolecules with this technique.…”