Global transcriptional analysis of S. mutans sugar transporters

The transport of carbohydrates by Streptococcus mutans is accomplished by the phosphoenolpyruvate-phosphotrasferase 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 carbohydrates. The results revealed that PTSs were responsible for transport of monosaccharides, disaccharides and sugar alcohols. 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, 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 polysaccharides, raffinose, stachyose and isomaltosaccharides. Compared to the PTS, the ABC transporters showed higher transcription under several tested conditions, suggesting that they might be transporting multiple substrates. Keywords: carbohydrate response Global transcriptional patterns were obtained following growth on different carbohydrates (monosaccharides: glucose, mannose, galactose and fructose; disaccharides: sucrose, lactose, maltose, trehalose and cellobiose; oligosaccharides: raffinose, stachyose and maltotriose; a sugar-alcohol: manitol). To assure reproducibility of the data, the cultures were always grown to the same optical density for RNA extraction and hybridization on Affymetrix microarrays. Fourteen different conditions were analyzed with 2, 4 or 10 replicates for each.