Effect of Nitrate, Fumarate, and Oxygen on the Formation of the Membrane-Bound Electron Transport System of Haemophilus parainfluenzae

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The composition of the membrane-bound electron transport system of Haemophilus parainfluenzae underwent modification in response to the terminal electron acceptor in the growth medium. H. parainfluenzae was able to grow with O2, nitrate, fumarate, pyruvate, and substrate amounts of nicotinamide adenine dinucleotide (NAD) as electron acceptors. When O2 served as the electron acceptor and its concentration was lowered below 20 μm, the bacteria formed more cytochromes b, c, a1, a2, and o than were present in the cells grown at 150 to 200 μm O2. Nitrate and nitrite reductase activities also appeared during growth at the low O2 concentrations in the absence of added nitrate. Cytochrome levels in cells grown anaerobically with fumarate, pyruvate, or NAD as terminal acceptors were similar to those formed in cells grown at low O2 concentrations. Cells grown with nitrate had higher levels of cytochromes c, b, and o, and of nitrate and nitrite reductases, than did cells grown with the other acceptors. The formation of cytochrome oxidase a2 was repressed by the presence of nitrate in the growth medium. The critical O2 concentration (the O2 concentration at which the rate of O2 uptake becomes demonstrably dependent on the O2 concentration) was about 100 μm in cells grown with nitrate and about 15 μm in cells grown with the other acceptors. A mutant of H. parainfluenzae was found to make about 10% as much cytochrome c as the wild type, and its formation of cytochrome a2 was not repressed by nitrate. The critical O2 concentration of the mutant was high when it was grown with nitrate, suggesting that the high levels of cytochrome c and the absence of cytochrome a2 from the wild type are not responsible for the high critical O2 concentration. The modifications of the respiratory system induced by changing the terminal electron acceptor were inhibited by the presence of chloramphenicol, which suggests that protein synthesis is involved.

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