Emission ((57)Co) Mössbauer spectroscopy as a tool for probing speciation and metabolic transformations of cobalt(II) in bacterial cells.

The emission ((57)Co) variant of Mössbauer spectroscopy, rarely used in biology-related studies, was applied to study binding and possible transformations of (57)Co(II) traces in live and dead (hydrothermally treated) cells of the rhizobacterium Azospirillum brasilense (strain Sp7) at T=80 K in frozen aqueous suspensions and as their dried residues. The Mössbauer parameters calculated from the spectra were compared with the similarly obtained data reported earlier for another A. brasilense strain, Sp245 (which differs from strain Sp7 by the ecological niche occupied in the rhizosphere and was found earlier to exhibit different metabolic responses under similar environmental conditions). Similarly to strain Sp245, live cells of strain Sp7, rapidly frozen 2 min and 1 h after their contact with (57)Co(2+) (measured in frozen suspensions), showed marked differences in their Mössbauer parameters, reflecting metabolic transformations of (57)Co(2+) occurring within an hour. However, the parameters for strains Sp7 (this work) and Sp245 (reported earlier), obtained under similar conditions, were found to significantly differ, implying dissimilarity in their metabolic response to Co(2+). This is in line with their different metabolic responses to several heavy metals, including Co(2+), detected earlier using Fourier transform infrared spectroscopy.