Spectroscopic and potentiometric characterization of cytochromes in two 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 c 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.Abbreviations E_m,7 midpoint potential at pH 7 and 25°C - H₄F tetrahydrofolate