Carbohydrate Uptake and Metabolism

The genes encoding the polysaccharide-hydrolyzing enzymes are often organized in an operon or regulon together with genes that encode the enzymes catalyzing the uptake of the extracellular hydrolytic products and the first intracellular steps in their catabolism. The Bacillus subtilis genome encodes about 23 secondary and 11 ATP-binding cassette (ABC) carbohydrate transporters. The major facilitator superfamily (MFS) comprises eight B. subtilis proteins of unknown carbohydrate specificity exhibiting significant similarity to the GalP/XylE subfamily. The genes encoding the polysaccharide-hydrolyzing enzymes are often organized in an operon or regulon together with genes that encode the enzymes catalyzing the uptake of the extracellular hydrolytic products and the first intracellular steps in their catabolism. Glycolysis is one of the most conserved metabolic pathways in living organisms. To conserve cellular resources, expression of most of the hundreds of carbohydrate catabolism genes is induced only when the corresponding carbohydrate is present in the growth medium. Expression of antiterminator-controlled genes or operons usually occurs from a constitutive promoter; transcription stops at a terminator located in the leader region of these genes and operons, providing very short transcripts. The carbohydrate transport systems operative in gram-positive and gram-negative bacteria are very similar and most likely developed early in evolution.