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PubMed2003

Characterization of Streptococcus mutans strains deficient in EIIAB Man of the sugar phosphotransferase system.

The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is the major sugar uptake system in oral streptococci. The role of EIIAB(Man) (encoded by manL) in gene regulation and sugar transport was investigated in Streptococcus mutans UA159. The manL knockout strain, JAM1, grew more slowly than the wild-type strain in glucose but grew faster in mannose and did not display diauxic growth, indicating that EIIAB(Man) is involved in sugar uptake and in carbohydrate catabolite repression. PTS assays of JAM1, and of strains lacking the inducible (fruI) and constitutive (fruCD) EII fructose, revealed that S. mutans EIIAB(Man) transported mannose and glucose and provided evidence that there was also a mannose-inducible or glucose-repressible mannose PTS. Additionally, there appears to be a fructose PTS that is different than FruI and FruCD. To determine whether EIIAB(Man) controlled expression of the known virulence genes, glucosyltransferases (gtfBC) and fructosyltransferase (ftf) promoter fusions of these genes were established in the wild-type and EIIAB(Man)-deficient strains. In the manL mutant, the level of chloramphenicol acetyltransferase activity expressed from the gtfBC promoter was up to threefold lower than that seen with the wild-type strain at pH 6 and 7, indicating that EIIAB(Man) is required for optimal expression of gtfBC. No significant differences were observed between the mutant and the wild-type background in ftf regulation, with the exception that under glucose-limiting conditions at pH 7, the mutant exhibited a 2.1-fold increase in ftf expression. Two-dimensional gel analysis of batch-grown cells of the EIIAB(Man)-deficient strain indicated that the expression of at least 38 proteins was altered compared to that seen with the wild-type strain, revealing that EIIAB(Man) has a pleiotropic effect on gene expression.

3' Flanking Region↗
PubMed2003

Genetic and biochemical characterization of the phosphoenolpyruvate:glucose/mannose phosphotransferase system of Streptococcus thermophilus.

In most streptococci, glucose is transported by the phosphoenolpyruvate (PEP):glucose/mannose phosphotransferase system (PTS) via HPr and IIAB(Man), two proteins involved in regulatory mechanisms. While most strains of Streptococcus thermophilus do not or poorly metabolize glucose, compelling evidence suggests that S. thermophilus possesses the genes that encode the glucose/mannose general and specific PTS proteins. The purposes of this study were to determine (i) whether these PTS genes are expressed, (ii) whether the PTS proteins encoded by these genes are able to transfer a phosphate group from PEP to glucose/mannose PTS substrates, and (iii) whether these proteins catalyze sugar transport. The pts operon is made up of the genes encoding HPr (ptsH) and enzyme I (EI) (ptsI), which are transcribed into a 0.6-kb ptsH mRNA and a 2.3-kb ptsHI mRNA. The specific glucose/mannose PTS proteins, IIAB(Man), IIC(Man), IID(Man), and the ManO protein, are encoded by manL, manM, manN, and manO, respectively, which make up the man operon. The man operon is transcribed into a single 3.5-kb mRNA. To assess the phosphotransfer competence of these PTS proteins, in vitro PEP-dependent phosphorylation experiments were conducted with purified HPr, EI, and IIAB(Man) as well as membrane fragments containing IIC(Man) and IID(Man). These PTS components efficiently transferred a phosphate group from PEP to glucose, mannose, 2-deoxyglucose, and (to a lesser extent) fructose, which are common streptococcal glucose/mannose PTS substrates. Whole cells were unable to catalyze the uptake of mannose and 2-deoxyglucose, demonstrating the inability of the S. thermophilus PTS proteins to operate as a proficient transport system. This inability to transport mannose and 2-deoxyglucose may be due to a defective IIC domain. We propose that in S. thermophilus, the general and specific glucose/mannose PTS proteins are not involved in glucose transport but might have regulatory functions associated with the phosphotransfer properties of HPr and IIAB(Man).

Amino Acid Sequence↗
PubMed2005

Novel activator of mannose-specific phosphotransferase system permease expression in Listeria innocua, identified by screening for pediocin AcH resistance.

To identify genes that are important for class IIa bacteriocin interaction and resistance in Listeria species, transposon Tn917 knockout libraries were constructed for Listeria innocua strain Lin11 and screened for mutants that are resistant to pediocin AcH. A highly resistant mutant (G7) (MIC > 20 microg/ml; 1,000-fold less susceptible than the wild type), in which the transposon integrated into the putative promoter of the lin0142 gene, was isolated. lin0142 is located immediately upstream of the mpt operon (mptA/mptC/mptD) that encodes the mannose-specific phosphoenolpyruvate-dependent phosphotransferase system permease EIItMan, which serves as a docking protein for class IIa bacteriocins. The transcription of the mpt operon is known to be positively controlled by sigma54 factor and ManR (a sigma54-associated activator). Transcripts for lin0142 and mpt were undetectable in the G7 mutant, based on quantitative real-time reverse transcriptase PCR analysis. When the wild-type lin0142 gene was expressed at a 7.9-fold-elevated level in the mutant via a multicopy-number plasmid, the level of mpt mRNA became 70% higher than that in the wild-type strain. In addition, the complementation strain reverted back to the pediocin AcH-susceptible phenotype. The levels of manR and rpoN (sigma54) mRNAs were not directly influenced by the level of lin0142 transcription. lin0142 is the only one of the three mpt regulatory genes whose transcription is induced, albeit slightly (1.2-fold), by glucose. The combined results show that the lin0142 gene encodes a novel activator of the mpt operon. The Lin0142 protein contains a winged-helix DNA-binding motif and is distantly related to the Crp-Fnr family of transcription regulators.

Amino Acid Sequence↗
PubMed1979

Effect of growth rate and glucose concentration on the activity of the phosphoenolpyruvate phosphotransferase system in Streptococcus mutans Ingbritt grown in continuous culture.

Streptococcus mutans Ingbritt was grown anaerobically in a chemostat with a glucose limitation, as well as with an excess of glucose (amino acid limitation) at dilution rates (D) between 0.05 and 0.4 h(-1) (mean generation time = 12 to 1.5 h). The glucose-limited culture produced cells having 1.5- to 6.0-fold greater glycolytic activity than the cells from the glucose-excess culture. The preferred substrate for these cells was glucose, with the glycolytic rate for sucrose being only slightly lower; the rate for fructose was half that of glucose. The glycolytic rate of the glucose-limited cells was maximum at D = 0.1 h(-1), with a decline in rate as the growth rate approached D = 0.4 h(-1). A comparison of the activity of phosphoenolpyruvate phosphotransferase system (PTS) in the two types of cells showed that the glucose-limited cells had 1.7- to 5.6-fold greater PTS activity for the three sugars than the glucose-excess-grown cells. Whereas little difference was seen between the three sugars with the latter cells, the glucose-PTS had the greatest activity with glucose-limited cells, with the maximum in cells grown at D = 0.1 h(-1). Comparison of the rate of sugar uptake in the chemostat with the rate of PTS transport activity in the cells at each growth rate demonstrated that only under conditions of slow growth with a glucose limitation was the PTS system capable of supporting growth on glucose. Furthermore, PTS activity in cells grown with an excess of glucose was insignificant when compared with glucose uptake during growth in the chemostat. This evidence supports the observation that S. mutans possesses at least one other system, in addition to the PTS, for the transport of glucose into the cell. The organism was, however, devoid of glucose-proton symport transport activity.

Biological Transport, Active↗
PubMed1979

Phosphoenolpyruvate-dependent sucrose phosphotransferase activity in Streptococcus mutans NCTC 10449.

A phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS) has been demonstrated, by an enzyme-coupled reaction and product isolation, in decryptified cell suspensions of the cariogenic microorganism Streptococcus mutans NCTC 10449. The apparent sucrose PTS reaction for sucrose-adapted, sucrose-challenged cells displayed saturation kinetics with an apparent Km of 7.14 x 10(-5) M, which was distinct from the Km of the glucose PTS activity of glucose-adapted, glucose-challenged cells. Both the sucrose and the glucose PTS activities appear to be inducible and under separate genetic control. The sucrose PTS reaction demonstrated in decryptified cells had an absolute requirement for phosphoenolpyruvate. Only 2-phosphoglycerate, the immediate glycolytic precursor of phosphoenolpyruvate, was found to substitute for phosphoenolpyruvate in this reaction in the absence of fluoride. The sucrose PTS activity of sucrose-adapted cells was competitively inhibited by raffinose and lactose; these same sugars had no effect on the apparent glucose PTS activity. Fructose was the only carbohydrate tested other than sucrose which elicited an apparent PTS reaction in sucrose-adapted cells. The product of the sucrose PTS reaction was isolated and behaved chromatographically on a Dowex-1-X8 column like a monophosphate ester. Alkaline phosphatase treatment of the presumptive sucrose monophosphate liberated a component which behaved chromatographically like free sucrose. Subsequent acid hydrolysis of this component produced moieties which behaved chromatographically like glucose and fructose.

Enzyme Induction↗
PubMed1980

Effect of growth conditions on sucrose phosphotransferase activity of Streptococcus mutans.

Sucrose and glucose phosphoenolpyruvate-dependent phosphotransferase (PTS) activities were studied in growing cultures of Streptococcus mutans serotype c and d/g cells adapted to either glucose or sucrose. Both acid production and optical absorbance were used to monitor growth in pH-controlled defined growth medium. The sucrose PTS activity appeared to be significant only under conditions of substrate limitation or slow growth as a result of low environmental pH. However, under environmental conditions which permitted rapid growth sucrose PTS activity appeared to be repressed, and only when the cells approached substrate-limited stationary phase after growth on high sucrose-supplemented medium was significant sucrose PTS activity again observed. A mutant apparently defective in sucrose PTS activity grew rapidly and produced acid under conditions of high environmental sucrose level but showed no sucrose PTS activity when the culture approached stationary phase. The mutant, however, after adaptation to glucose, demonstrated significant glucose PTS once the culture had attained the stationary growth phase. During diauxie growth in the presence of glucose and sucrose, there were sequential apparent inductions and repressions of glucose and sucrose PTS activities corresponding to decreases and increases of growth rate on the two substrates. Thus, S. mutans possesses at least two transport mechanisms for each substrate studied. One system (PTS) functions under conditions permitting slow growth and another functions under conditions permitting rapid growth.

Enzyme Induction↗
PubMed1982

Evidence for the involvement of proton motive force in the transport of glucose by a mutant of Streptococcus mutans strain DR0001 defective in glucose-phosphoenolpyruvate phosphotransferase activity.

Streptococcus mutans DR0001 and a glucose-phosphotransferase (PTS)-defective mutant, DR0001/6, were grown anaerobically in a chemostat with a glucose limitation at dilution rates (D) of 0.04 to 0.6 h(-1) (mean generation time, 17 to 1.2 h). The mutant possessed only 15% of glucose-PTS activity of the wild type and gave cell yields (19%) less than those of the wild type. Glucose-PTS activity in strains DR0001 was maximum at D = 0.1 h(-1) and was adequate to account for transport in the chemostat at all dilution rates except D = 0.6 h(-1), at which it was 80% of the actual glucose uptake activity. The mutant DR0001/6, on the other hand, possessed only sufficient glucose-PTS activity to sustain growth at below D = 0.1 h(-1), indicating the presence of an alternate transport activity. This was confirmed in glycolytic rate experiments with washed cells, which demonstrated that the mutant showed rates 11- to 27-fold higher than that accountable via glucose-PTS activity alone. The wild-type organism contained both a high (K(s), 6.7 to 8.0 muM)- and a low (K(s), 57 to 125 muM)-affinity transport system, whereas the glucose-PTS-defective mutant contained only the low-affinity system (K(s), 62 to 133 muM). The glucose-PTS was shown to be the high-affinity system. Glucose uptake by the mutant was unaffected by 8 mM sodium arsenate, 10 mM azide, and 10 mM dinitrophenol but was completely inhibited by 0.05 mM sodium iodoacetate. Glycolysis in the organism was almost completely inhibited by 0.25 mM N',N' -dicyclohexylcarbodiimide (DCCD), indicating the involvement of an ATPase in glucose uptake. The ionophores carbonylcyanide-m-chlorophenylhydrazone and tetrachlorosali-cylanilide were inhibitory at concentrations of 10 muM, suggesting that a proton gradient was important in the transport process. Higher levels of DCCD and the ionophores were required to inhibit the wild-type organism to the same degree. A mechanism is proposed for the alternative transport system whereby proton motive force is created by the extrusion of protons by the DCCD-sensitive ATPase and glucose is transported down a proton gradient in a symport with protons.

Adenosine Triphosphatases↗
PubMed1982

Properties of Streptococcus mutans Ingbritt growing on limiting sucrose in a chemostat: repression of the phosphoenolpyruvate phosphotransferase transport system.

Growth of Streptococcus mutans Ingbritt on limiting sucrose in a chemostat at dilution rates of 0.05 to 0.4 h-1 (mean generation time, 14 to 1.7 h) resulted in a heterofermentative pattern of metabolic end products. During fast growth, lactic acid was the major end product, whereas at slower growth rates, acetic and formic acids, as well as ethanol, increased to be major end products. The patterns obtained were similar to those seen with the same organism growing on glucose. The glycolytic rate by washed cells was maximum at the lowest dilution rates and decreased as the cells were made to grow faster. Transport of sucrose, glucose, and fructose via the phosphoenolpyruvate phosphotransferase system (PTS) was repressed during growth on sucrose after growth on glucose. Uptake rates suggested that sucrose was transported in the PTS as the intact disaccharide. Comparison of the rate of sugar uptake in the chemostat with the rate of PTS activity in the cells at each growth rate indicated that the PTS was capable of supporting growth only at a dilution rate of 0.05 h-1. Growth on sucrose at faster growth rates required the activity of a second transport system, supporting our earlier observations with glucose that S. mutans contains at least two sugar transport systems.

Biological Transport↗
PubMed1984

Role of the phosphoenolpyruvate-dependent glucose phosphotransferase system of Streptococcus mutans GS5 in the regulation of lactose uptake.

When Streptococcus mutans GS5 was grown in equimolar (5 mM) amounts of glucose and lactose, a classical diauxic growth curve was obtained. Glucose was taken up during the first growth phase, followed by a 60-min lag, and then lactose was transported. Synthesis of lactose phosphotransferase system (PTS) enzymes was repressed until the complete exhaustion of glucose, indicative of an inducer exclusion mechanism of repression. The enzyme phospho-beta-galactosidase, however, was found in small amounts even in the presence of glucose. Repression was not observed when GS5 was grown in equimolar amounts of fructose and lactose. Although fructose was taken up preferentially, synthesis of the lactose PTS occurred from the onset of growth in these sugars. It is proposed that a component of the glucose PTS may be a regulatory factor in lactose transport. Glucose PTS- mutants did not display diauxic growth in glucoselactose mixtures and, in fact, transported the disaccharide preferentially.

Fructose↗
PubMed1984

Transport of glucose and mannose by a common phosphoenolpyruvate-dependent phosphotransferase system in Streptococcus mutans GS5.

Decryptified cells of Streptococcus mutans GS5 transport glucose, mannose, and fructose by constitutive phosphoenolpyruvate-dependent phosphotransferase systems (PTSs). Although the non-metabolizable glucose analog 2-deoxyglucose is transported by a PTS, alpha-methylglucose is not taken up by strain GS5. The transport of [14C]mannose and [14C]glucose was almost totally blocked by the heterologous sugars, indicating that these substrates may share a common PTS permease. [14C]fructose transport, however, was not inhibited by large excesses of glucose, indicating the existence of a separate fructose PTS. All "tight" glucose PTS- mutant clones studied were also unable to transport mannose, whereas some "leaky" glucose PTS- clones also were leaky for mannose phosphorylation. Fructose transport in most of these mutant strains was unimpaired, indicating that genetic lesions did not involve soluble (cytoplasmic) PTS components.

Binding, Competitive↗
PubMed1984

Glucose phosphoenolpyruvate-dependent phosphotransferase system of Streptococcus mutans GS5 studied by using cell-free extracts.

The glucose phosphotransferase system (PTS) of Streptococcus mutans GS5 has been partially characterized, using fractions derived from cells treated with the muramidase mutanolysin. Membranes retained functional PTS enzymes for the phosphoenolpyruvate-dependent phosphorylation of glucose, fructose, and mannose. This was confirmed by assaying membranes directly for enzyme I (EI) and enzyme IIglc (EIIglc) by employing specific phosphoryl-exchange reactions for each factor. Membranes prepared from glucose PTS- mutants, however, were either deficient in glucose phosphorylation or reflected the "leakiness" displayed by whole cells. Mutant membranes were unable to catalyze the glucose:glucose 6-phosphate transphosphorylation reaction, indicating a defective EIIglc in these fractions. Although total cellular EI activities in the mutant clones were about the same as that measured for the wild-type strain by employing the pyruvate:phosphoenolpyruvate phosphoryl-exchange reaction, mutant membranes were found to possess less than 10% of the specific EI activity of wild-type membranes. The cytoplasmic fractions of mutants, however, displayed markedly increased specific activities for this enzyme when compared with wild-type extracts. These results strongly suggest a molecular association of EI with a normal membrane protein, perhaps EIIglc, that is absent in mutants. This would explain the absence of fructose PTS activity in glucose PTS- mutant membranes despite the fact that whole cells of these clones are normal for this transport function.

Carbon Radioisotopes↗
PubMed1984

Lactose transport in Streptococcus mutans: isolation and characterization of factor IIIlac, a specific protein component of the phosphoenolpyruvate-lactose phosphotransferase system.

The transport of lactose in Streptococcus mutans is mediated via an inducible phosphoenolpyruvate-lactose phosphotransferase system. This system requires for catalytic activity a membrane fraction (enzyme II), two general proteins called enzyme I and HPr, and a soluble specific protein termed factor IIIlac. This protein factor was purified from S. mutans ATCC 27352 by chromatographies on DEAE-cellulose, hydroxylapatite, Ultrogel AcA 34, and phosphocellulose. The purified protein migrated as a single band with a molecular weight of 10,000 on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and urea. The molecular weight calculated from the amino acid composition was 10,541. Gel filtration of the native protein gave a molecular weight of 41,500. Its isoelectric point was ca. 4.70. A specific antiserum was prepared against purified factor IIIlac. Immunodiffusion experiments revealed that only cellular extracts from lactose-grown cells contained factor IIIlac. A cross-reaction was observed with all of the S. mutans strains tested as well as with Streptococcus sanguis 10556, Streptococcus lactis 11454, and Staphylococcus aureus 6538. No precipitin band was observed with extracts of Streptococcus salivarius, Streptococcus faecalis, Lactobacillus casei, and Bacillus subtilis.

Amino Acids↗
PubMed1984

Identification and properties of distinct sucrose and glucose phosphotransferase enzyme II activities in Streptococcus mutans 6715g.

We investigated phosphoenolpyruvate-dependent phosphotransferase system enzyme II activities for sucrose and glucose in Streptococcus mutans 6715g. Two integral membrane proteins, enzyme IIscr and enzyme IIglc, each specific for its sugar substrate, sucrose or glucose, were identified by their abilities to catalyze specific sugar:sugar-phosphate exchange reactions. Some of the properties of these two transport proteins are also presented.

Cell Membrane↗
PubMed1988

Starvation-induced stimulation of sugar uptake in Streptococcus mutans is due to an effect on the activities of preexisting proteins of the phosphotransferase system.

We examined the effects of sugar concentration in the medium on sugar uptake and phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) activities in Streptococcus mutants GS-5. Kinetic analyses of sucrose uptake in cells harvested under conditions of sucrose excess or sucrose limitation showed that increased uptake under the latter condition was almost completely due to an increase in the Vmax of the high-affinity PTS. In a series of experiments in which cells growing under conditions of sucrose or glucose excess were shifted to a medium lacking sugar, starvation resulted in a stimulation of sugar uptake and a parallel increase in PTS activity. These starvation-induced increases in PTS-mediated uptake were not affected by the presence of either chloramphenicol or rifampin during the starvation period, indicating that neither protein nor RNA synthesis was necessary for the stimulation. In vivo labeling experiments with 32Pi revealed that uptake stimulation during starvation was accompanied by a loss of acid-stable phosphate covalently bound to the phosphocarrier protein HPr of the PTS. We conclude, therefore, that stimulation of PTS-mediated uptake of sucrose and glucose during sugar limitation in S. mutans GS-5 is at least partially the result of increased activities of preexisting PTS proteins and that this may be due, at least in part, to dephosphorylation of a previously identified site in S. mutans HPr that can be phosphorylated by an ATP-dependent kinase.

Biological Transport, Active↗
PubMed1991

Repeated DNA sequence involved in mutations affecting transport of sucrose into Streptococcus mutans V403 via the phosphoenolpyruvate phosphotransferase system.

Mutants of Streptococcus mutans V403 defective in the intracellular sucrose-6-phosphate hydrolase (product of the scrB gene) are sensitive to sucrose because of the intracellular accumulation of the phosphorylated sugar. Using a scrB mutant prepared by allelic exchange, we have isolated and characterized a number of sucrose-resistant revertants. One such mutant was found to lack the ability to transport sucrose into the cell via the phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS). Genetic analysis of this strain revealed this lesion to be linked to the scrB gene. This was corroborated by the physical demonstration of an insertion mutation very near scrB. Taken together with DNA sequence information (Y. Sato, F. Poy, G. R. Jacobson, and H. K. Kuramitsu, J. Bacteriol. 171:263-271, 1989), our results indicated that all of the mutations characterized were located in the adjoining scrA gene which encodes the membrane-associated, sugar-specific enzyme II (EIIsucrose) component of the sucrose PTS in S. mutans. Biochemically, such a genetic lesion disables the sucrose PTS and prevents sucrose from entering the cell by this system. In this paper, we detail the nature of two independent insertion mutations and conclude them to be the result of duplicative transposition events into the scrA gene. This region of the chromosome was amplified and purified in large quantities by using the polymerase chain reaction. Examination of the amplified DNA revealed that the two independent insertion mutations were composed of sequences that were indistinguishable by size and by restriction site endonuclease maps. Their insertion points in the scrA gene were approximately 200 bp apart. The amplified DNA fragment was also used as a probe to demonstrate the presence of five copies of this element on the S. mutans V403 chromosome. A second strain, S. mutans V310, also was found to carry similarly arranged, multiple copies of this sequence on its chromosome, suggesting a clonal origin of V403 and V310. The small size of this sequence, its presence in multiple copies on the V403 chromosome, and its ability to duplicate itself semiconservatively into remote sites argue compellingly that it is an insertion sequence element. One such insertion mutant, with a defective sucrose PTS, was tested for virulence in rats and was found to cause caries at levels similar to those of the wild-type strain.

Animals↗
PubMed1992

Isolation, characterization, and nucleotide sequence of the Streptococcus mutans mannitol-phosphate dehydrogenase gene and the mannitol-specific factor III gene of the phosphoenolpyruvate phosphotransferase system.

Streptococcus mutans, the causative agent of dental caries, utilizes carbohydrates by means of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The PTS facilitates vectorial translocation of metabolizable carbohydrates to form the corresponding sugar-phosphates, which are subsequently converted to glycolytic intermediates. The PTS consists of both sugar-specific and sugar-independent components. Complementation of an Escherichia coli mtlD mutation with a streptococcal recombinant DNA library allowed isolation of the mannitol-1-phosphate dehydrogenase gene (mtlD) and the adjacent sugar-specific mannitol factor III gene (mtlF) from S. mutans. Subsequent transposon mutagenesis of the complementing DNA fragment with Tn5seq1 defined the region that encodes the mtlD-complementing activity, the streptococcal mtlD gene. Nucleotide sequence analysis of this region revealed two complete open reading frames (ORFs) from within the streptococcal mannitol PTS operon. One ORF encodes the mtlD gene product, a 43.0-kDa protein which exhibits similarity to the E. coli and Enterococcus faecalis mannitol-1-phosphate dehydrogenases. The second ORF encodes a 15.8-kDa protein which exhibits similarity to mannitol factor III proteins from several bacterial species. In vitro transcription-translation assays were used to produce proteins of the sizes predicted by the streptococcal ORFs. These data indicate that the S. mutans mannitol PTS utilizes an enzyme II-factor III complex similar to the mannitol system found in other gram-positive organisms, as opposed to that of E. coli, which utilizes an independent enzyme II system.

Amino Acid Sequence↗
PubMed2000

Identification of the operon for the sorbitol (Glucitol) Phosphoenolpyruvate:Sugar phosphotransferase system in Streptococcus mutans.

Transposon mutagenesis and marker rescue were used to isolate and identify an 8.5-kb contiguous region containing six open reading frames constituting the operon for the sorbitol P-enolpyruvate phosphotransferase transport system (PTS) of Streptococcus mutans LT11. The first gene, srlD, codes for sorbitol-6-phosphate dehydrogenase, followed downstream by srlR, coding for a transcriptional regulator; srlM, coding for a putative activator; and the srlA, srlE, and srlB genes, coding for the EIIC, EIIBC, and EIIA components of the sorbitol PTS, respectively. Among all sorbitol PTS operons characterized to date, the srlD gene is found after the genes coding for the EII components; thus, the location of the gene in S. mutans is unique. The SrlR protein is similar to several transcriptional regulators found in Bacillus spp. that contain PTS regulator domains (J. Stülke, M. Arnaud, G. Rapoport, and I. Martin-Verstraete, Mol. Microbiol. 28:865-874, 1998), and its gene overlaps the srlM gene by 1 bp. The arrangement of these two regulatory genes is unique, having not been reported for other bacteria.

Amino Acid Sequence↗