Growth and Carbohydrate Metabolism of Sulfobacilli

The moderately thermophilic acidophilic bacteria Sulfobacillus thermosulfidooxidans, strain 1269, S. thermosulfidooxidanssubsp. asporogenes, strain 41, and the thermotolerant strain S. thermosulfidooxidanssubsp. thermotolerans K1 prefer mixotrophic growth conditions (the concomitant presence of ferrous iron, thiosulfate, and organic compounds in the medium). In heterotrophic and autotrophic growth conditions, these sulfobacilli can grow over only a few culture transfers. In cell-free extracts of these sulfobacilli, key enzymes of the Embden–Meyerhof–Parnas, pentose-phosphate, and Entner–Doudoroff pathways were found. The role of a particular pathway depended on the cultivation conditions. All of the enzymes assayed were most active under mixotrophic conditions in the presence of Fe²⁺and glucose, suggesting the operation of all of the three major pathways of carbohydrate metabolism under these conditions. However, the operation of the Entner–Doudoroff pathway in strain 41 was restricted under mixotrophic conditions. After the first culture transfer from mixotrophic to heterotrophic conditions, the utilization of glucose occurred only via the Embden–Meyerhof–Parnas and Entner–Doudoroff pathways. After the first culture transfer from mixotrophic to autotrophic conditions, the activity of carbohydrate metabolism enzymes decreased in all of the strains studied; in strain K1, only the glycolytic pathway remained operative. The high activity of fructose-bisphosphate aldolase, remaining in strain 41 cells under these conditions, suggests the involvement of this enzyme in the reactions of the Calvin cycle or of gluconeogenesis.