Influence of Aerobic and Phototrophic Growth Conditions on the Distribution of Glucose and Fructose Carbon into the Entner-Doudoroff and Embden-Meyerhof Pathways in Rhodopseudomonas sphaeroides

In aerobically and phototrophically growing cells of Rhodopseudomonas sphaeroides, glucose and fructose catabolism were studied by means of enzyme analysis, radiorespirometry and incorporation of specifically-labelled glucose and fructose into spheroidene fractions, into alanine and into valine. Bacteria grown on glucose or fructose possessed all the enzymes necessary for sugar catabolism via the Entner-Doudoroff pathway. Bacteria grown on fructose also contained an inducible 1-phosphofructokinase, indicating that fructose was degraded via fructose 1-phosphate. Fructose was catabolized via both the Embden-Meyerhof and Entner-Doudoroff pathways. The contribution of each pathway to fructose breakdown was influenced by the growth conditions: under phototrophic conditions fructose was catabolized predominantly via the Embden-Meyerhof pathway; under aerobic conditions it was catabolized mainly via the Entner-Doudoroff pathway. This change in the major fructose catabolic pathway was paralleled by fructose-1, 6-bisphosphate aldolase activity: the activity was high in phototrophically growing cells and low in aerobically growing cells. Glucose, on the other hand, was catabolized via the Entner-Doudoroff pathway under both phototrophic and aerobic conditions.