Fructose transport in Bacillus subtilis

The transport of fructose in Bacillus subtilis was studied in various mutant strains lacking the following activities: ATP‐dependent fructokinase (fruC), the fructose 1‐phosphate kinase (fruB) the phosphofructokinase (pfk), the enzyme I of the phosphoenolpyruvate phosphotransferase system (the thermosensitive mutation ptsIl), and a transport activity (fruA). Combinations of these mutations indicated that the transport of fructose in Bacillus subtilis is tightly coupled to its phosphorylation either in fructose 1‐phosphate, identified in vivo and in vitro or in fructose 6‐phosphate identified by indirect lines of evidence. These steps of fructose metabolism were shown to depend on the activity of the enzyme I of the phosphoenolpyruvate phosphotransferase systems. The fruA mutations affect the transport of fructose when the bacteria are submitted to catabolite repression. The mutations were localized on the chromosome of Bacillus subtilis in a cluster including the fruB gene. When grown in a medium supplemented by a mixture of potassium glutamate and succinate the fruA mutants are able to carry on the two vectorial metabolisms generating fructose 6‐phosphate as well as fructose 1‐phosphate. A negative search of strictly negative transport mutants in fruA strains indicated that more than two structural genes are involved in the transport of fructose.