Coordinated Regulation of the EII Man and fruRKI Operons of Streptococcus mutans by Global and Fructose-Specific Pathways

The glucose/mannose-phosphotransferase system (PTS) permease EIIMan encoded bymanLMN in the dental caries pathogenStreptococcus mutans has a dominant influence on sugar-specific, CcpA-independent catabolite repression (CR). Mutations inmanL affect energy metabolism and virulence-associated traits, including biofilm formation, acid tolerance, and competence. Using promoter::reporter fusions, expression of themanLMN and thefruRKI operons, encoding a transcriptional regulator, a fructose-1-phosphate kinase and a fructose-PTS permease EIIFru , respectively, was monitored in response to carbohydrate source and in mutants lacking CcpA, FruR, and components of EIIMan . Expression of genes for EIIMan and EIIFru was directly regulated by CcpA and CR, as evinced byin vivo andin vitro methods. Unexpectedly, not only was thefruRKI operon negatively regulated by FruR, but also so wasmanLMN . Carbohydrate transport by EIIMan had a negative influence on expression ofmanLMN but notfruRKI . In agreement with the proposed role of FruR in regulating these PTS operons, loss offruR orfruK substantially altered growth on a number of carbohydrates, including fructose. RNA deep sequencing revealed profound changes in gene regulation caused by deletion offruK orfruR . Collectively, these findings demonstrate intimate interconnection of the regulation of two major PTS permeases inS. mutans and reveal novel and important contributions of fructose metabolism to global regulation of gene expression.IMPORTANCE The ability ofStreptococcus mutans and other streptococcal pathogens to survive and cause human diseases is directly dependent upon their capacity to metabolize a variety of carbohydrates, including glucose and fructose. Our research reveals that metabolism of fructose has broad influences on the regulation of utilization of glucose and other sugars, and mutants with changes in certain genes involved in fructose metabolism display profoundly different abilities to grow and express virulence-related traits. Mutants lacking the FruR regulator or a particular phosphofructokinase, FruK, display changes in expression of a large number of genes encoding transcriptional regulators, enzymes required for energy metabolism, biofilm development, biosynthetic and degradative processes, and tolerance of a spectrum of environmental stressors. Since fructose is a major component of the modern human diet, the results have substantial significance in the context of oral health and the development of dental caries.