DIFFERENTIAL CYTOCHROME CONTENT AND REDUCTASE-ACTIVITY IN GEOSPIRILLUM-BARNESII STRAIN SES3

The protein composition, cytochrome content, and reductase activity in the dissimilatory selenate-reducing bacterium Geospirillum barnesii s train SeS3, grown with thiosulfate, nitrate, selenate, or fumarate as the terminal electron acceptor, was investigated. Comparison of seven high-molecular-mass membrane proteins (105.3, 90.3, 82.6, 70.2, 67.4, 61.1, and 57.3 kDa) by SDS-PAGE showed that their detection was depend ent on the terminal electron acceptor used. Membrane fractions from ce lls grown on thiosulfate contained a 70.2-kDa c-type cytochrome with a bsorbance maxima at 552, 522, and 421 nm. A 61.1-kDa c-type cytochrome with absorption maxima at 552, 523, and 423 nm was seen in membrane f ractions from cells grown on nitrate. No c-type cytochromes were detec ted in membrane fractions of either selenate- or fumarate-grown cells. Difference spectra, however, revealed the presence of a cytochrome b( 554) (absorption maxima at 554, 523, and 422 nm) in membrane fractions from selenate-grown cells and a cytochrome b(556) (absorption maxima at 556, 520, and 416 nm) in membrane fractions from fumarate-grown cel ls, Analysis of reductase activity in the different membrane fractions showed variability in substrate specificity. However, enzyme activity was greatest for the substrate on which the cells had been grown (e.g ., membranes from nitrate-grown cells exhibited the greatest activity with nitrate). These results show that protein composition, cytochrome content, and reductase activity are dependent on the terminal electro n acceptor used for growth.