The transport of carbohydrates by Streptococcus mutans is accomplished by the phosphoenolpyruvatephosphotransferase system (PTS) and ATP-binding cassette (ABC) transporters. To undertake a global transcriptional analysis of all S. mutans sugar transporters simultaneously, we used a whole-genome expression microarray. Global transcription profiles of S. mutans UA159 were determined for several monosaccharides (glucose, fructose, galactose, and mannose), disaccharides (sucrose, lactose, maltose, and trehalose), a ␤-glucoside (cellobiose), oligosaccharides (raffinose, stachyose, and maltotriose), and a sugar alcohol (mannitol). The results revealed that PTSs were responsible for transport of monosaccharides, disaccharides, ␤-glucosides, and sugar alcohol. Six PTSs were transcribed only if a specific sugar was present in the growth medium; thus, they were regulated at the transcriptional level. These included transporters for fructose, lactose, cellobiose, and trehalose and two transporters for mannitol. Three PTSs were repressed under all conditions tested. Interestingly, five PTSs were always highly expressed regardless of the sugar source used, presumably suggesting their availability for immediate uptake of most common dietary sugars (glucose, fructose, maltose, and sucrose). The ABC transporters were found to be specific for oligosaccharides, raffinose, stachyose, and isomaltosaccharides. Compared to the PTSs, the ABC transporters showed higher transcription under several tested conditions, suggesting that they might be transporting multiple substrates.Numerous studies have implicated Streptococcus mutans as the principal causative agent of human dental caries. It is well known that host diet is important for S. mutans cariogenicity, and sugar metabolism of this bacterium plays a key role in the formation of caries. S. mutans is able to metabolize a wide range of carbohydrates that may originate from dietary sources or from host macromolecules. If the diet is rich in sugars, especially sucrose, the end product of sugar metabolism is mostly lactic acid that can lead to demineralization of tooth enamel. Therefore, sugar transport and metabolism by this bacterium are directly related to the onset and development of dental caries.In bacteria, sugar substrates are taken up by ATP-binding cassette (ABC) transporters, galactoside-pentose hexuronide (GPH) translocators, and, most commonly, phosphoenolpyruvate-sugar phosphotransferase systems (PTSs). The bacterial PTSs are responsible for the binding, transmembrane transport, and phosphorylation of numerous sugar substrates. These systems are also involved in the regulation of a variety of metabolic and transcriptional processes (29, 37). The PTS consists of two nonspecific energy-coupling components, enzyme I (EI) and a heat-stable protein (HPr), as well as several sugarspecific multiprotein permeases known as EII. In most cases, EIIA and EIIB are located in the cytoplasm, while EIIC acts as a membrane channel (37). Fourteen PTS systems have been found in S. mutans UA1...