Anaerobic growth of a Rhodopseudomonas species in the dark with carbon monoxide as sole carbon and energy substrate.

A species of Rhodopseudomonas that grows under strict anaerobic conditions in the dark and requires CO was isolated from lake and pond sediments. Although anaerobic growth in the dark occurs in a chemically defined mineral medium with CO as the only carbon and energy source, growth is stimulated by adding trypticase. Under these conditions, cells exhibit a generation time of 6.7 hr and reach a final concentration of 1 to 3 X 10(9) cells per ml of liquid medium. Resting suspensions of CO-grown cells metabolize about 6.7 mumol of CO per mg of protein in 1 hr and produce equimolar amounts of CO2 and H2 according to the equation CO + H2O leads to CO2 + H2. As predicted by this equation, when cells were suspended in tritium-labeled water containing potassium phosphate buffer at pH 7.0 and incubated with pure CO, 3H2 gas was produced at linear rate with a constant specific activity.