Electron Transport System of the Protoheme-requiring Anaerobe Bacteroides melaninogenicus

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Abstract
Protoheme is essential for the growth of some strains of B. melaninogenicus. At low concentrations in the growth medium, protoheme determines the doubling time, total cell yield and amount of cytochrome/bacterium. At high protoheme concentrations, the doubling time, total cell yield and amount of enzymati-cally reducible cytochrome appear to remain nearly constant, and protoheme is accumulated by the cell. The accumulated protoheme can support the growth of the bacterium for at least 8 generations in a protoheme-free medium. When growth and cytochrome content are proportional during growth at low protoheme concentrations, the bacteria incorporate 10-20 % of the total available protoheme into a membrane-bound respiratory system. This respiratory system includes cytochrome c, a CO-binding pigment and possibly flavoproteins. The pigments can be reversibly reduced by NADH or endogenous metabolism and can be oxidized anaeroDically by fumarate or by shaking in air. Electron transport is inhibited by 2-n-nonyl-4-hydroxy-quinoline-N-oxide.