Achim Kröger

Energy metabolism and biosynthesis of Vibrio succinogenes growing with nitrate or nitrite as terminal electron acceptor

Abstract1.Growth of Vibrio succinogenes with nitrate as terminal electron acceptor was found to be a function of the following two catabolic reactions: (a)n

Hydrogenase from Vibrio succinogenes, a nickel protein

HCO _2^ - + NO _3^ - + H^ + to CO_2 + NO _2^ - + H_2 O

ATP formation coupled to caffeate reduction by H2 in Acetobacterium woodii NZva16

n(b)n

Phosphorylation and phosphate-ATP exchange catalyzed by the ATP synthase isolated from Wolinella succinogenes

3HCO _2^ - + NO _2^ - + 5H^ + to 3CO_2 + NH _4^ + + 2H_2 O.

Structural properties of the proteoliposomes catalyzing electron transport from formate to fumarate

nThe latter reaction (b) was responsible for growth with nitrite.2.Either succinate or fumarate could serve as sole carbon source during growth with nitrate or nitrite. Biosynthesis from succinate proceeded via fumarate. The ATP requirement for cell synthesis from succinate was equal to that calculated earlier for growth with fumarate as carbon source and electron acceptor (Brounder et al. 1982).3.The cell yield at infinite dilution rate (Ymax) as obtained with chemostat cultures was 8.5g dry cells/mol formate with either nitrate or nitrite as acceptor. This value amounts to 60% of that measured earlier with fumarate as acceptor (Mell et al. 1982).4.Membrane vesicles prepared from V. succinogenes catalyzed electron transport from H2 to nitrate. The reaction was dependent on the menaquinone present in the membrane.5.Electron transport with H2 and nitrite was coupled to the phosphorylation of ADP. The P/H2 ratio with nitrite was 40% of that measured with fumarate as acceptor using the same preparation. The phosphorylation but not the electron transport was abolished by an uncoupling agent.

Cell yields of Vibrio succinogenes growing with formate and fumarate as sole carbon and energy sources in chemostat culture

Abstract1.With fumarate as the terminal electron acceptor and either H2 or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.2.Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.3.Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.4.In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.5.During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H2 or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO2.6.The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H2 or formate were not detected in the bacterium.