Carbohydrate Metabolism in Bacteria

Carbohydrate metabolism in bacteria—Use of differences in carbohydrate metabolism for identifying bacteria.

ALL BACTERIA MUST UTILIZE THE ENERGY SOURCES IN THEIR ENVIRONMENT IN ORDER TO PRODUCE ATP. ATP IS REQUIRED FOR ALL OF THE BIOSYNTHETIC PROCESSES THAT BACTERIA USE FOR THEIR MAINTENANCE AND REPRODUCTION. BACTERIA PRODUCE ENZYMES THAT ALLOW THEM TO OXIDIZE ENVIRONMENTAL ENERGY SOURCES; HOWEVER, THE ENERGY SOURCES THAT DIFFERENT BACTERIA USE DEPENDS ON THE SPECIFIC ENZYMES THAT EACH BACTERIA PRODUCE.

Heterotrophic bacteria often use carbohydrates as energy sources. Many bacteria use glucose, a monosaccharide or simple sugar, because many bacteria possess the enzymes required for the degradation and oxidation of this sugar. Fewer bacteria are able to use complex carbohydrates like disaccharides (lactose or sucrose) or polysaccharides (starch). Disaccharides and polysaccharides are simple sugars that are linked by glycosidic bonds; bacteria must produce enzymes to cleave these bonds such that the simple sugars that result can be transported into the cell. If the bacteria cannot produce these enzymes then the complex carbohydrate is not used. For example, lactose is a disaccharide consisting of monomeric glucose and monomeric galactose linked by a glycosidic bond. Bacteria that use lactose must first produce the enzyme lactase (beta-galactosidase) to break the glycosidic bond between these monomers. Starch is a large polysaccharide consisting of long chains of monomeric glucose linked by glycosidic bonds. Bacteria that use starch produce an exoenzyme, alpha amylase, that break these bonds such that free monomeric glucose is produced.

Each bacterium has its own collection of enzymes that enable it to use diverse carbohydrates; this is often exploited in the identification of bacterial species. One can determine if a given bacterial species can utilize a given carbohydrate by checking for the presence of byproducts that are produced...