SPECTROSCOPIC AND POTENTIOMETRIC CHARACTERIZATION OF CYTOCHROMES IN 2 SPOROMUSA SPECIES AND THEIR EXPRESSION DURING GROWTH ON SELECTED SUBSTRATES

The homoacetogenic bacteria Sporomusa ovata and Sporomusa sphaeroides were grown on betaine, betaine + formate, and acetoin in the absence of carbon dioxide, and the formation of membrane-bound cytochromes was determined. In S. sphaeroides, the growth substrate had little influence on the expression of cytochromes. In contrast, membranes from betaine- or acetoin-grown S. ovata cells had an 11- or 3-fold higher cytochrome b content than cells grown on betaine + formate. The cytochrome e content was reduced below the detection level after growth on the latter two substrates. The cytochromes in the membranes of S. sphaeroides and S. ovata were characterized by low-temperature difference spectroscopy, hemochrome difference spectroscopy, and redox potentiometry. Membranes of S. ovata were shown to contain two b-type cytochromes with E(m, 7) = - 153 +/- 10 mV and E(m,7) = - 226 +/- 14 mV and two c-type cytochromes with E(m,7) = - 86 +/- 6 mV and E(m, 7) = - 265 +/- 10 mV. In S. sphaeroides also two b-type cytochromes with E(m, 7) = - 165 +/- 7 mV and E(m, 7) = -241 +/- 2 mV and two c-type cytochromes with E(m, 7) = -101 +/- 4 mV and E(m, 8.5) = - 338 +/- 9 mV could be distinguished. Cell extracts of S. sphaeroides were shown to contain all the enzymes of the acetyl-CoA (Wood) pathway. The degradation pathways of the substrates tested and the possible role of the cytochromes are discussed.