The Presence and Function of Cytochromes in Selenomonas ruminantium, Anaerovibrio lipolytica and Veillonella alcalescens

Strains of Selenomonas ruminantium, Anaerovibrio lipolytica and Veillonella alcalescens contained cytochrome b. Peaks corresponding to cytochromes a and a carbon monoxide-binding pigment were also observed. By means of dual-wavelength experiments with crude membrane fractions it was established that cytochrome b functioned in anaerobic electron transport to fumarate. In V. alcalescens and one strain of S. ruminantium which reduced nitrate, anaerobic electron transport to nitrate was found. Glycerol 1-phosphate and NADH were active as hydrogen donors for cytochrome b reduction in glycerol-grown A. lipolytica, lactate and pyruvate were active in lactate-grown V. alcalescens, and NADH was active in lactose-grown S. ruminantium. Oxidative phosphorylation associated with these electron transfer systems might explain the high molar growth yields previously found for these micro-organisms. Fermentation products were measured in supernatant fluids of cultures grown in the presence and absence of nitrate. Nitrate did not influence the fermentation of lactose to lactate by S. ruminantium, and inhibited propionate formation by V. alcalescens.