Carbon metabolism in Chromatium.

The purple photosynthetic sulfur bacterium, Chromatium, will grow only in the light and under anaerobic conditions. This organism can grow on an inorganic medium utilizing CO2 as the sole carbon source in the presence of reduced inorganic sulfur compounds. Some reduced carbon compounds can be utilized for the growth of this organism but only in the light and under anaerobic conditions. In this case, reduced sulfur is not required and the reduced carbon compounds can serve concomitantly as a source of carbon and reducing power. The initial concept of the mechanism of bacterial photosynthesis involving the photolysis of water was postulated by van Niel (1, 2). He proposed that a reducing fragment designated as (H) and an oxidizing fragment (OH) were produced and that the latter was involved in the oxidation of sulfide to elemental sulfur. The reaction sequence was written as follows (Equations 1 to 4):