Sucrose- and fructose-specific effects on the transcriptome of Streptococcus mutans probed by RNA-Seq

For Streptococcus mutans, the major etiologic agent of human dental caries, sucrose is the carbohydrate that contributes in the most significant manner to establishment, persistence and virulence of the organism. However, because this organism produces multiple extracellular sucrolytic enzymes that can release hexoses from sucrose, it has not been possible to study the specific effects of sucrose transport and metabolism on gene expression in the absence of carbohydrates that by themselves can elicit catabolite repression and induce expression of multiple genes. Employing RNA deep sequencing (RNA-Seq) technology and mutants that lacked particular sucrose-metabolizing enzymes, we compared the transcriptomes of S. mutans growing on glucose, fructose or sucrose as the sole carbohydrate. The results provide a variety of new insights into the impact of sucrose transport and metabolism by S. mutans, including the likely expulsion of fructose after sucrose internalization and hydrolysis, and identified a set of genes that are differentially regulated by sucrose versus fructose. The findings significantly enhance our understanding of the genetics and physiology of this cariogenic pathogen. mRNA profiling of a set of mutants lacking secreted sucrolytic enzymes, growing on media supported solely by glucose, fructose or sucrose.