Transcriptional Regulation of the Cellobiose Operon of Streptococcus mutans

Abstract

The ability of Streptococcus mutans to catabolize cellobiose, a ␤-linked glucoside generated during the hydrolysis of cellulose, is shown to be regulated by a transcriptional regulator, CelR, which is encoded by an operon with a phospho-␤-glucosidase (CelA) and a cellobiose-specific sugar phosphotransferase system (PTS) permease (EII Cel ). The roles of CelR, EII Cel components, and certain fructose/mannose-PTS permeases in the transcriptional regulation of the cel locus were analyzed. The results revealed that (i) the celA and celB (EIIB Cel ) gene promoters require CelR for transcriptional activation in response to cellobiose, but readthrough from the celA promoter contributes to expression of the EII Cel genes; (ii) the EII Cel subunits were required for growth on cellobiose and for transcriptional activation of the cel genes; (iii) CcpA plays little direct role in catabolite repression of the cel regulon, but loss of specific PTS permeases alleviated repression of cel genes in the presence of preferred carbohydrates; and (iv) glucose could induce transcription of the cel regulon when transported by EII Cel . CelR derivatives containing amino acid substitutions for five conserved histidine residues in two PTS regulatory domains and an EIIA-like domain also provided important insights regarding the function of this regulator. Based on these data, a model for the involvement of PTS permeases and the general PTS proteins enzyme I and HPr was developed that reveals a critical role for the PTS in CcpAindependent catabolite repression and induction of cel gene expression in S. mutans.The pathogen primarily responsible for human tooth decay, Streptococcus mutans, can utilize a wide variety of carbohydrates found in the diet and in host-derived macromolecules (6, 16). The S. mutans genome contains more than a dozen phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS) permeases dedicated to the internalization and phosphorylation of simple sugars (22,26,27). S. mutans depends on the PTS for the acquisition of energy sources and for acid production through glycolysis, an integral part of its pathogenic mechanisms. A recent study probing the expression of various PTS permeases in S. mutans cells grown in a variety of carbohydrates supports that most of these permeases are subject to transcriptional regulation (5).S. mutans can assimilate a number of ␤-glucosides, including cellobiose, esculin, arbutin, and salicin (8, 21). Cellobiose utilization pathways have been of particular interest because of their potential for the development of alternative energy sources (9, 23). A previous study identified a genetic locus in S. mutans UA159 that is required for the catabolism of cellobiose, including genes for phospho-␤-glucosidase (celA), a putative transcriptional regulator (celR), and the B, A, and C domains of the cellobiose PTS enzyme EII Cel (celB, celC, and celD), respectively (21). Deletion of celA or celD resulted in loss of growth on cellobiose. Hence, utilization of cellobiose by S. mutans consis...

YidC1 and YidC2 are functionally distinct proteins involved in protein secretion, biofilm formation and cariogenicity of Streptococcus mutans

“…The yidC2 gene was fused to the celB promoter and placed into the gtfA locus of the DyidC2 mutant (AH398) chromosome to create strain SP10, where expression of yidC2 is under the control of the carboncatabolite-repressible celB promoter (Zeng & Burne, 2009). Strain SP20 was produced by replacing yidC1 in strain SP10 with a spectinomycin marker (see Fig.…”

Modification of Streptococcus mutans Cnm by PgfS Contributes to Adhesion, Endothelial Cell Invasion, and Virulence

“…Other accessory proteins, such as Gap1, Gap2, and Gap3, are also involved in the formation of a stable complex, which allows proper Fap1 maturation and secretion (25). Similarly complex mechanisms for glycosylation of the human platelet-binding protein GspB and the fibrinogen-binding protein Srr1 have been observed in Streptococcus gordonii and Streptococcus agalactiae, respectively (41,47). While homologs of these glycosylation systems are found in other Gram-positive organisms (40), none of the genes encoding these glycosyltransferases are present in S. mutans.…”

Comprehensive Mutational Analysis of Sucrose-Metabolizing Pathways in Streptococcus mutans Reveals Novel Roles for the Sucrose Phosphotransferase System Permease

“…In most low-GϩC Gram-positive bacteria, CCR is effected primarily by catabolite control protein A, CcpA, which regulates gene expression by binding to conserved catabolite response elements (CRE) in the promoter regions of CCRsensitive genes, although many alternative mechanisms to selectively regulate carbohydrate uptake and catabolic pathways exist. In S. mutans, CcpA does play an important role in the global control of gene expression (26), but CcpA-independent mechanisms involving the PTS phosphocarrier protein HPr and various EII permeases play dominant roles in CCR, regulating catabolic pathways such as the fruAB operon, the fructose/mannose-PTS encoded by levDEFG (22,27), and transport and catabolism of cellobiose (28) and lactose (29). There are data to support that sucrose may be a preferred carbohydrate source that can elicit CCR in S. mutans (30)(31)(32)(33).…”