Carbohydrate Degradation Pathways in Thiobacillus A2 Grown on Various Sugars

A detailed radiorespirometric and enzymological analysis was made of the wild-type and GFI strains of Thiobacillus A2 grown on numerous sugars. The wild-type used the EmbdenMeyerhof, Entner-Doudoroff and pentose phosphate pathways for glucose oxidation only after culture on glucose. The fast-growing strain GFI used all three pathways after growth on glucose, maltose or fructose. The wild-type grown on a wide range of pentoses, hexoses, disaccharides, a trisaccharide and a mixture of glucose and maltose oxidized glucose by means of the Entner-Doudoroff pathway (68 to 90%) and pentose phosphate pathway (10 to 32 yo). The key enzyme determining the presence or absence of the Embden-Meyerhof pathway was 6-phosphofructokinase. Other mechanisms, such as a phosphoketolase pathway, were shown to be unimportant, even during growth on pentoses. Arabinose was metabolized via hexose phosphate synthesis. The mechanisms of regulation of sugar metabolism and the energetic significance of alternative pathways are discussed.