Growth and carbohydrate metabolism of sulfobacilli

The moderately thermophilic acidophilic bacteria Sulfobacillus thermosulfid ooxidans, strain 1269, S. thermosulfidooxidans subsp. "asporogenes," strain 41 and the thermotolerant strain S. thermosulfidooxidans subsp. "thermotol erans" K1 prefer mixotrophic growth conditions (the concomitant presence of ferrous iron, thiosulfate, and organic compounds in the medium). In hetero trophic 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-D oudoroff pathways were found. The role of a particular pathway depended on the cultivation conditions. All of the enzymes assayed were most active und er mixotrophic conditions in the presence of Fe2+ and glucose, suggesting t he operation of all of the three major pathways of carbohydrate metabolism under these conditions. However, the operation of the Entner-Doudoroff path way in strain 41 was restricted under mixotrophic conditions. After the fir st culture transfer from mixotrophic to heterotrophic conditions, the utili zation of glucose occurred only via the Embden-Meperhof-Parnas and Entner-D oudoroff pathways. After the first culture transfer from mixotrophic to aut otrophic conditions, the activity of carbohydrate metabolism enzymes decrea sed in all of the strains studied; in strain K1, only the glycolytic pathwa y remained operative. The high activity of fructose-bisphosphate aldolase, remaining in strain 41 cells under these conditions, suggests the involveme nt of this enzyme in the reactions of the Calvin cycle or of gluconeogenesi s.