Which carbohydrate does Streptococcus mutans utilize to form dextran?

Streptococcus mutans, a bacterium commonly associated with dental caries, utilizes sucrose to form dextran. When sucrose is present, the bacteria can ferment it to produce energy and, importantly, use its glucose component as a substrate to synthesize dextran. Dextran is a polysaccharide that plays a crucial role in the formation of dental plaque, contributing to the ability of S. mutans to adhere to the tooth surface.

The process involves the enzyme dextransucrase, which catalyzes the transfer of glucose from sucrose to growing dextran chains. This ability to produce dextran from sucrose allows the bacterium to establish a biofilm on teeth, which can ultimately lead to tooth decay if not managed properly. The other carbohydrate options, although they may serve various roles in metabolism, do not provide the specific linkage properties needed for dextran synthesis in the same way that sucrose does.