Analysis of Sucrose Catabolism in Klebsiella pneumoniae and in Scr+ Derivatives of Escherichia coli K12

In contrast to a previous report, strains of Klebsiella pneumoniae were found to take up and phosphorylate the disaccharide sucrose via the phosphoenolpyruvate-dependent carbohydrate phosphotransferase system (PTS). In addition to the two soluble and general components enzymeI and HPr of the PTS, a sucrose-specific enzymeIIScr (gene scrA), together with the enzymeIII, coded for by the gene crr, were needed for the vectorial phosphorylation of sucrose to generate intracellular sucrose 6-phosphate. This sugar phosphate is hydrolysed by a hydrolase (invertase, gene scrB) to generate glucose 6-phosphate and free fructose. The latter is converted to fructose 6-phosphate by an ATP-dependent fructokinase (gene scrK), an enzyme which is part of the sucrose and not of the fructose catabolic pathway. Analysis of different mutants of K. pneumoniae strain 1033, and of Escherichia coli K12 derivatives carrying R'scr plasmids isolated from K. pneumoniae, showed that the genes scrA, B, and K, together with a gene scrR for a repressor, form a genetic unit located on the chromosome of K. pneumoniae. These genes and the corresponding sucrose metabolic pathway are very similar to a previously described scr system encoded on plasmid pUR400 and found in other enteric bacteria.