EC Slater Institute, BioCentrum, University of Amsterdam, Plantage Muidergracht 12, 1018 TV Amsterdam, The Netherlands1
TNO Voeding, Department of Applied Microbiology and Gene Technology, PO box 360 3700 AJ Zeist, The Netherlands2
Author for correspondence: Peter H. Pouwels (TNO Voeding). Tel: +31 30 6944 924. Fax: +31 30 6944 466. e-mail: Pouwels{at}voeding.tno.nl
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ABSTRACT |
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Keywords: mannose PTS, fructose PTS, CcpA, sugar transport, regulation
Abbreviations: 2DG, 2-deoxyglucose; CR, catabolite repression; mannose PTS, phosphoenolpyruvate:mannose phosphotransferase system; PEP, phosphoenolpyruvate
a Present address: Institut National de la Recherche Agronomique, Unité Flore Lactique et Environnement Carné, CRJ, Domaine de Vilvert, 78350 Jouy-en-Josas, France.
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INTRODUCTION |
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It is now well established that in Bacillus subtilis and other low-GC-content Gram-positive bacteria, the dominant CR pathway involves one of the components of the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS), the protein HPr, and a transcription regulator, CcpA (for a review see Stülke & Hillen, 1999 ). HPr can be phosphorylated at a Ser-46 residue by an ATP-dependent HPr kinase activated by fructose 1,6-bisphosphate (Deutscher & Saier, 1983
; Galinier et al., 1998
; Reizer et al., 1984
, 1998
). HPr(Ser-P) was shown to interact with CcpA, resulting in a protein complex which can bind to cis-acting catabolite-responsive elements (cre) located in the promoter regions of many catabolic operons (Deutscher et al., 1995
; Fujita et al., 1995
; Jones et al., 1997
), thereby preventing transcription. The signal for activation of the HPr(Ser-P)/CcpA pathway is generated during glycolysis, especially when the rate of transport and phosphorylation of the repressing sugars is high.
In B. subtilis the glucose-specific PTS, comprising HPr and EI and the EIIGlc complex, plays an important role in transport and phosphorylation of glucose (Gonzy-Tréboul et al., 1991 ). In lactic acid bacteria or sugar-fermenting streptococci on the other hand, transport and phosphorylation of glucose is carried out by the mannose PTS (HPr, EI and an EIIMan complex). PTSs have been identified in a number of lactic acid bacteria, e.g. Lactobacillus casei (Veyrat et al., 1994
), Lactobacillus sakei (Lauret et al., 1996
), Lactobacillus curvatus (Veyrat et al., 1996
), Lactococcus lactis (Thompson & Chassy, 1985
), Tetragenococcus halophila (Abe & Uchiba, 1989
) and several species of oral streptococci (for a review see Vadeboncoeur & Pelletier, 1997
). Amongst the species described above, the gene cluster encoding the EIIMan complex of the mannose PTS has been cloned and characterized for L. curvatus (Veyrat et al., 1996
) and Streptococcus salivarius (Lortie et al., 2000
). The L. curvatus cluster comprises the genes manABCD encoding the sugar-specific EIIA, EIIB, EIIC and EIID proteins of the EIIMan complex. In S. salivarius, the man gene cluster comprises the gene manL encoding the
protein and the genes manMNO encoding respectively EIIC and EIID of the EIIMan complex and a putative regulator of the cluster.
From the major role of the EIIMan complex in glucose transport and phosphorylation in lactic acid bacteria, it may be assumed that the activity of this PTS would affect CR. Indeed, mutations rendering the EIIMan complex inactive resulted in the loss of the preferential use of glucose over several carbon sources such as lactose or ribose in L. casei (Gosalbes et al., 1997 ; Veyrat et al., 1994
) or xylose in T. halophila (Abe & Uchiba, 1989
). It has also been shown that mutations affecting the expression of S. salivarius mannose PTS components, especially the
subunit, have a pleiotropic effect on the synthesis of several metabolic enzymes (Gauthier et al., 1990
; Lapointe et al., 1993
) as well as on urease activity (Chen et al., 1998
) and on an inducible fructose PTS activity (Bourassa & Vadeboncoeur, 1992
). In several instances, a regulatory role in CR has been suggested for the EIIMan complex. However, no information on the relationship between activity of the EIIMan complex and CcpA-dependent CR mediated by glucose is available for S. salivarius. Therefore, the mechanisms by which the EIIMan complex is implicated in regulatory functions are not satisfactorily defined.
We have previously demonstrated a role of CcpA in the transcription regulation of the xyl regulon in Lactobacillus pentosus (Chaillou et al., 1998 ; Lokman et al., 1997
). Recently, we have isolated a 2-deoxyglucose-resistant (2DGR) mutant of L. pentosus, named LPE6, which showed a lack of PEP-dependent phosphorylation of mannose. We showed that mannose PTS activity was restored in LPE6 when plasmid pMJ18, expressing the manB gene encoding the EIIBMan subunit of the L. curvatus EIIMan complex, was introduced (Chaillou et al., 1999
). This result indicated that LPE6 presumably contained a mutation in the EIIBMan domain. In our previous study, we reported the effect of EIIMan mutations on the uptake of xylose, but we did not investigate the possible consequences of these mutations on the utilization of other sugars and on CR. We have now further characterized mutant LPE6 and compared the effect of the EIIBMan mutation with that of a ccpA deletion. We present in this study results demonstrating that the mannose PTS of L. pentosus regulates expression of the fructose-specific PTS independently of CcpA.
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METHODS |
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Growth conditions.
During all the experiments described in this study, cells were cultivated on the Lactobacillus synthetic rich MCD medium (Lauret et al., 1996 ), supplemented with 50 mg l-1 each of L-aspartic and L-glutamic acid, which are essential amino acids for species related to Lactobacillus plantarum (Ledesma et al., 1977
). All carbohydrates were added at a final concentration of 0·5% (w/v) and erythromycin (5 µg ml-1) was added when necessary. All incubations were carried out at 37 °C in non-shaken tubes containing either 25 ml (growth, phosphorylation and uptake studies) or 5 ml (enzyme assays) of MCD medium. Inoculations were performed by diluting an MCD culture (OD600 1·0; obtained after 824 h incubation depending on the energy source used) 1/100 into fresh medium.
Preparation of permeabilized cells.
Bacterial cultures were cultivated as described above, washed twice with ice-cold 50 mM potassium phosphate buffer (pH 6·5) containing 2 mM MgSO4 (KPM buffer), resuspended in 1/100 of culture volume in KPM containing 20% (w/v) glycerol, and rapidly frozen in liquid nitrogen and kept at -80 °C until use. After thawing, cells were washed once with KPM buffer and then resuspended to a final OD600 of 50 in 50 mM potassium phosphate buffer (pH 6·5) containing 12·5 mM NaF, 5 mM MgCl2 and 2·5 mM dithiothreitol. Cells were permeabilized as follows. First, 2·5 µl toluene/acetone (1:9, v/v) was added per 250 µl cell suspension and the mixture was vortexed for 5 min at 4 °C. Cells were then rapidly centrifuged (150 g, at 4 °C for 2 min) and the supernatant was discarded. This step was necessary to remove the high cytoplasmic PEP pool of L. pentosus. The cell pellet was resuspended again in the same buffer (OD600 50) and treated once more with toluene/acetone as described above. After 5 min of vortexing, permeabilized cells were kept on ice.
PEP- and ATP-dependent 14C-labelled carbohydrate phosphorylation assay.
For each assay, 2·5 µl, 5 µl and 10 µl of permeabilized cells (OD600 50) were incubated in a final volume of 100 µl 50 mM potassium phosphate buffer (pH 6·5) containing 12·5 mM NaF, 5 mM MgCl2, 2·5 mM dithiothreitol, 10 mM PEP or ATP, and 10 mM 14C-labelled carbohydrate (specific activity 200 d.p.m. nmol-1). After incubating for 1530 min at 37 °C, the phosphorylated carbohydrates were separated on Dowex AG 1-X2 columns as described previously (Postma, 1977 ), and the radioactivity was determined by liquid scintillation counting.
Uptake of D-[U-14C]fructose in starved cells.
Cells for uptake studies were cultivated, harvested, washed and frozen as described above for the preparation of permeabilized cells. For transport measurements, cells were first washed once with KPM buffer and resuspended at a concentration of 0·5 mg dry wt ml-1 in 100 µl KPM buffer. This cell suspension was incubated for 2 min at 37 °C and transport was initiated by addition of D-[U-14C]fructose at the concentrations indicated (specific activity ranged from 330 d.p.m. nmol-1 to 38000 d.p.m. nmol-1). After 15 s of uptake, 2 ml ice-cold 0·1 M LiCl was added to the cells and the samples were rapidly filtered through glass-fibre filters (Whatman GF/F) and washed with an equal amount of ice-cold 0·1 M LiCl. The radioactivity was determined by liquid scintillation counting.
Enzyme assays.
ß-Glucosidase and ß-galactosidase activities were determined at 37 °C in 750 µl KPM buffer containing 1020 µl permeabilized cells (OD600 50) and 5 mM p-nitrophenyl ß-D-glucopyranoside or o-nitrophenyl ß-D-galactopyranoside, respectively. Adding 250 µl 1 M Na2CO3 stopped the reaction and the A410 was measured. The activity is expressed as nmol p-nitrophenol formed min-1 (mg dry wt)-1.
Radiochemicals.
D-[U-14C]Glucose (11·5 GBq mmol-1), D-[U-14C]mannose (10·6 GBq mmol-1), D-[U-14C]fructose (11·9 GBq mmol-1), 2-deoxy-D-[U-14C]glucose (11·1 GBqmmol-1), and N-acetyl-D-[1-14C]glucosamine (2·11 GBq mmol-1) were obtained from Amersham.
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RESULTS |
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Effect of growth substrate on PTS activities in L. pentosus MD353
Next we determined the effect of the growth conditions on the four PTS activities detected in L. pentosus. This experiment was carried out with wild-type bacteria as reference (Fig. 1). A similar pattern of activities was observed for glucose, mannose and N-acetylglucosamine. In each case the activities were increased about 1·6-fold when MD353 cells were cultivated on these substrates, as compared to the activities in cells grown on other energy sources. PEP-dependent phosphorylation of fructose increased 1·8-fold in cells grown on fructose compared to that of cells grown on ribose, xylose, glycerol or gluconate. Fructose PTS activity was strongly decreased in cells grown on glucose, mannose and N-acetylglucosamine. These results strongly suggested that fructose is taken up via a PTS different from that of glucose, mannose and N-acetylglucosamine. Moreover, the data further indicated that these three sugars exert a repressive effect on fructose PTS activity.
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Kinetics of fructose uptake in starved cells of MD353 and LPE6
Previous reports have shown that fructose can be a substrate for PTS transporters of the mannose class in various micro-organisms (Bourassa et al., 1990 ; Erni et al., 1987
; Martin-Verstraete et al., 1990
; Wehmeier et al., 1995
). If fructose could also be a substrate of EIIMan in L. pentosus, possibly its transport and phosphorylation via EIIMan could lead to a different level of fructose PTS activity in cells of MD353 grown on fructose compared to that in LPE6. In order to determine whether fructose is a substrate of EIIMan, we measured the kinetics of fructose uptake in cells of MD353 and LPE6 grown on either glucose or fructose. An EadieHofstee plot of fructose uptake in glucose-grown cells of MD353 (Fig. 2a
) revealed the presence of two transport systems for fructose: a high-affinity transport system [apparent Km 52±1 µM and Vmax 4·2±0·3 nmol min-1 (mg dry wt)-1] and a low-affinity transport system [apparent Km 300±18 µM and Vmax 12·9±0·3 nmol min-1 (mg dry wt)-1]. In contrast, the kinetics of fructose uptake in glucose-grown cells of LPE6 (Fig. 2a
) revealed the presence of a single high-affinity transport system [apparent Km 46±5 µM and Vmax 47±3 nmol min-1 (mg dry wt)-1]. Since we could characterize the mutation of LPE6 as being presumably located in the EIIBMan domain, these results imply that the low-affinity uptake system for fructose of L. pentosus corresponds to EIIMan. An Eadie-Hofstee plot of fructose uptake in fructose-grown cells of MD353 and LPE6 (Fig. 2b
) revealed the presence of the high-affinity system in both strains [apparent Km 52·5±4 µM and Vmax 81±9 nmol min-1 (mg dry wt)-1, and apparent Km 52·1±5 µM and Vmax 155±11 nmol min-1 (mg dry wt)-1 for MD353 and LPE6, respectively]. However, the low rate of fructose uptake via the low-affinity transport system cannot be measured separately in the presence of the high-affinity system in fructose-grown cells of MD353 under our assay conditions. Finally, a comparison of the kinetics of fructose uptake in glucose-grown (Fig. 2a
) and fructose-grown (Fig. 2b
) cells of LPE6 showed a 3·2-fold induction of the high-affinity system by fructose.
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DISCUSSION |
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Data presented in Fig. 1 showed that the rate of phosphorylation of fructose in wild-type bacteria was increased in fructose medium compared to non-PTS sugars and was strongly repressed in the presence of EIIMan substrates. In LPE6, phosphorylation of fructose was higher while that of EIIMan substrates was greatly decreased compared to wild-type bacteria. Finally, expression in LPE6 of manB on a multi-copy plasmid largely restored the capacity to phosphorylate EIIMan substrates but strongly suppressed phosphorylation of fructose (Table 2
). To further our understanding of these phenomena, we studied fructose PTS activity and fructose uptake in the different strains. Fructose-uptake studies in wild-type bacteria revealed the presence of two transport systems for fructose, a high-affinity transport system and a low-affinity transport system. By comparing fructose uptake rates in wild-type bacteria with those in LPE6, EIIMan was shown to be responsible for the low-affinity system, while the high-affinity system constitutes a different transport system, which we will refer to as EIIFru.
Our data clearly demonstrate that EIIFru activity in L. pentosus is dependent on two factors: one involving a 3·2-fold induction by growth on fructose, and another one involving a negative regulation mediated by the presence of glucose/mannose/N-acetylglucosamine in the growth medium. Mutant LPE6 appeared to lack the negative regulation of EIIFru activity. The mechanism of this negative regulation is not known but the data presented in Fig. 1 suggest that the phosphorylation state of the EIIMan complex might be an important factor. In the presence of gluconate, glycerol, xylose or ribose, EIIFru activity was elevated in comparison with that in the presence of sugars that are substrates of EIIMan. It should be noted that PEP-dependent phosphorylation of glucose, mannose and N-acetylglucosamine could be detected in glycerol- or ribose/xylose/gluconate-grown cells, indicating that the EIIMan complex is active under these growth conditions. Since no transport and phosphorylation via EIIMan occurs under these conditions, most likely the EIIMan complex is phosphorylated, while it is unphosphorylated in the presence of the substrates of EIIMan.
In this study we have also investigated the role of the global regulator CcpA on sugar transport and phosphorylation, and compared the effects of CcpA and the EIIMan complex on EIIFru activity and on CR of two metabolic enzyme activities. EIIMan and EIIFru activities were similar in a ccpA mutant (LPE4) and in wild-type bacteria. These results indicate that the ccpA mutation has no effect on EIIMan and EIIFru activity in L. pentosus. They also indicate that the growth impairment of mutant LPE4 on various sugars did not result from inefficient transport and phosphorylation of these compounds. It has recently been shown that B. subtilis ccpA mutants grow poorly in minimal media due to an inefficient utilization of glutamate as the source of nitrogen (Faires et al., 1999
). The results presented here might indicate that the growth deficiency of LPE4 is caused by decreased nitrogen assimilation, as shown for the B. subtilis ccpA mutants.
Our results showed that expression of ß-glucosidase and ß-galactosidase is down-regulated by a CcpA-dependent mechanism in the presence of glucose, mannose and fructose. The repression mediated by glucose and mannose (EIIMan substrates) on these enzymes was partially relieved in LPE6 whereas the fructose-mediated repression was increased. Moreover, fructose-mediated repression of the two enzymes was also partially relieved in LPE6/pMJ18, a strain that showed low fructose PTS activity and inefficient growth on fructose. The evidence presented here suggests that fructose-mediated repression of ß-glucosidase and ß-galactosidase expression in L. pentosus is dependent on EIIFru activity, whereas the glucose/mannose-mediated repression is dependent on EIIMan activity. Thus, repression of ß-glucosidase and ß-galactosidase expression may result from inefficient metabolism of a particular compound due to a lower transport and phosphorylation activity. As referred to in the Introduction, the paradigm of HPr(Ser-P)/CcpA-dependent CR in B. subtilis describes that this regulatory pathway is activated by accumulation of phosphorylated glycolytic intermediates (Galinier et al., 1998 ; Stülke & Hillen, 1999
), and dephosphorylation of HPr on the His-15 residue (this form of HPr does not interact with CcpA; Deutscher et al., 1995
), two conditions which are met during sugar transport via the PTS. Thus, considering the predominant role of EIIMan and EIIFru in transport and phosphorylation of glucose/mannose and fructose, we conclude that these two PTSs play a major role, but an indirect one, in the CcpA-mediated CR of ß-glucosidase and ß-galactosidase expression in L. pentosus.
To summarize, we conclude that (i) regulation of EIIFru synthesis by EIIMan sugars in L. pentosus is CcpA-independent, and (ii) the negative regulation of EIIFru activity is associated with a functional and active EIIMan complex. The negative effect exerted by EIIMan is more pronounced when manB encoding the EIIBMan subunit is expressed from a multi-copy plasmid. A similar phenomenon has been previously observed for several S. salivarius mutants deficient in EIIMan activity (Bourassa & Vadeboncoeur, 1992 ). In these mutants, which lacked a cytoplasmic component of EIIMan called
(Bourassa et al., 1990
; Vadeboncoeur & Gauthier, 1987
), expression of an inducible fructose PTS was derepressed in glucose- and fructose-grown cells. Although the role of CcpA in regulating the fructose PTS was not investigated in this species, its induction in the absence of
suggests that the synthesis of EIIFru in S. salivarius and L. pentosus might be regulated via a similar mechanism. In both species, the nature of the regulatory component is still an open question. Nevertheless, our results presented in Fig. 1
and Table 4
suggest a critical role of the phosphorylation state of the EIIBMan subunit in the regulation of EIIFru activity in L. pentosus. However, another PTS component, HPr, might also be responsible for the EIIFru activities described in this work. For instance, differences in the relative levels of phosphorylation of HPr at His-15 and Ser-46, resulting from the mutation in EIIBMan and from overexpression of manB, due to the presence of multiple copies of pMJ18, could possibly modify the regulatory function of HPr. Indeed, expression of several bacterial genes encoding substrate-specific PTSs has been shown to be regulated by a mechanism involving phosphorylation of an antiterminator protein by HPr-15 or by one of the EII components belonging to the specific PTS (for a review see Stülke & Hillen, 1998
). A molecular genetic analysis of the L. pentosus EIIMan- and EIIFru-encoding genes, as well as of the ptsHI operon, is needed to unravel this regulatory mechanism in more detail.
In this report we have provided evidence that the EIIMan complex is an important component of CR in L. pentosus. First of all, as a major actor in the catabolism of glucose, mannose and N-acetylglucosamine, the EIIMan complex provides a strong signal to the global CcpA-dependent CR pathway. Similarly, the EIIFru complex is an important component of the fructose-mediated CcpA-dependent CR. In addition, the EIIMan complex is specifically involved in inhibition of the EIIFru activity. Our data strongly suggest a critical role of the phosphorylation state of the EIIBMan subunit in this regulatory control. Further experiments designed to test the role of this subunit should yield a better insight into the global mechanisms of CR in lactobacilli.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Bourassa, S. & Vadeboncoeur, C.(1992). Expression of an inducible enzyme II fructose and activation of a cryptic enzyme II glucose in glucose-grown cells of spontaneous mutants of Streptococcus salivarius lacking the low-molecular-mass of IIIman, a component of the phosphoenolpyruvate:mannose phosphotransferase system. J Gen Microbiol 138, 769-777.[Medline]
Bourassa, S., Gauthier, L., Giguère, R. & Vadeboncoeur, C.(1990). A IIIMan protein is involved in the transport of glucose, mannose and fructose by oral streptococci. Oral Microbiol Immunol 5, 288-297.[Medline]
Chaillou, S., Lokman, B. C., Leer, R. J., Posthuma, C., Postma, P. W. & Pouwels, P. H.(1998). Cloning, sequence analysis and characterization of the genes involved in isoprimeverose metabolism in Lactobacillus pentosus. J Bacteriol 180, 2312-2320.
Chaillou, S., Pouwels, P. H. & Postma, P. W.(1999). Transport of D-xylose in Lactobacillus pentosus, Lactobacillus casei and Lactobacillus plantarum: evidence for a mechanism of facilitated diffusion via the phosphoenolpyruvate:mannose phosphotransferase system. J Bacteriol 181, 4768-4773.
Chen, Y. Y., Hall, T. H. & Burne, R. A.(1998). Streptococcus salivarius urease expression: involvement of the phosphoenolpyruvate:sugar phosphotransferase system. FEMS Microbiol Lett 165, 117-122.[Medline]
Deutscher, J. & Saier, M. H.Jr(1983). ATP-dependent, protein kinase-catalysed phosphorylation of a seryl residue in HPr, the phosphoryl carrier protein of the phosphotransferase system in Streptococcus pyogenes. Proc Natl Acad Sci USA 80, 6790-6794.[Abstract]
Deutscher, J., Küster, E., Bergstedt, U., Charrier, V. & Hillen, W.(1995). Protein kinase-dependent HPr/CcpA interaction links glycolytic activity to carbon catabolite repression in Gram-positive bacteria. Mol Microbiol 15, 1049-1053.[Medline]
Erni, B., Zanolari, B. & Kocher, H. P.(1987). The mannose permease of Escherichia coli consists of three different proteins. Amino acid sequence and function in sugar transport, sugar phosphorylation, and penetration of phage lambda DNA. J Biol Chem 262, 5238-5247.
Faires, N., Tobisch, S., Bachem, S., Martin-Verstraete, I., Hecker, M. & Stülke, J.(1999). The catabolite control protein CcpA controls ammonium assimilation in Bacillus subtilis. J Mol Microbiol Biotechnol 1, 141-148.[Medline]
Fujita, Y., Miwa, Y., Galinier, A. & Deutscher, J.(1995). Specific recognition of the Bacillus subtilis gnt cis-acting catabolite-responsive element by a protein complex formed between CcpA and seryl-phosphorylated HPr. Mol Microbiol 17, 953-960.[Medline]
Galinier, A., Kravanja, M., Engelmann, R., Hengsterberg, W., Kilhoffer, M.-C., Deutscher, J. & Haiech, J.(1998). New protein kinase and protein phosphatase families mediate signal transduction in bacterial catabolite repression. Proc Natl Acad Sci USA 95, 1823-1828.
Gauthier, L., Bourassa, S., Brochu, D. & Vadeboncoeur, C.(1990). Control of sugar utilization in oral streptococci. Properties of phenotypically distinct 2-deoxyglucose-resistant mutants of Streptococcus salivarius. Oral Microbiol Immunol 5, 352-359.[Medline]
Gonzy-Tréboul, G., de Waard, J. H., Zagorec, M. & Postma, P. W.(1991). The glucose permease of the phosphotransferase system of Bacillus subtilis: evidence for IIGlc and IIIGlc domains. Mol Microbiol 5, 1241-1249.[Medline]
Gosalbes, M. J., Monedero, V., Alpert, C. A. & Pérez-Martínez, G.(1997). Establishing a model to study the regulation of the lactose operon in Lactobacillus casei. FEMS Microbiol Lett 148, 83-89.[Medline]
Jones, B. E., Dossonet, V., Küster, E., Hillen, W., Deutscher, J. & Klevit, R. E.(1997). Binding of the catabolite repressor protein CcpA to its DNA target is regulated by phosphorylation of its corepressor HPr. J Biol Chem 272, 26530-26535.
Lapointe, R., Frenette, M. & Vadeboncoeur, C.(1993). Altered expression of several genes in -defective mutants of Streptococcus salivarius demonstrated by two-dimensional gel electrophoresis of cytoplasmic proteins. Res Microbiol 144, 305-316.[Medline]
Lauret, R., Morel-Deville, F., Berthier, F., Champonier-Verges, M., Postma, P. W., Ehrlich, S. D. & Zagorec, M.(1996). Carbohydrate utilization in Lactobacillus sake. Appl Environ Microbiol 62, 1922-1927.[Abstract]
Ledesma, O. V., De Ruiz, A. P., Oliver, G., De Siori, G. S., Raibaud, P. & Galpin, J. V.(1977). A synthetic medium for comparative nutritional studies of lactobacilli. J Appl Bacteriol 42, 123-133.[Medline]
Lokman, B. C., van Santen, P., Verdoes, J. C., Krüse, J., Leer, R. J., Posno, M. & Pouwels, P. H.(1991). Organization and characterization of the three genes involved in D-xylose catabolism in Lactobacillus pentosus. Mol Gen Genet 230, 161-169.[Medline]
Lokman, B. C., Heerikhuisen, M., Leer, R. J., van den Broek, A., Borsboom, Y., Chaillou, S., Postma, P. & Pouwels, P. H.(1997). Regulation of expression of the Lactobacillus pentosus xylAB-operon. J Bacteriol 179, 5391-5397.[Abstract]
Lortie, L.-A., Pelletier, M., Vadeboncoeur, C. & Frenette, M.(2000). The gene encoding in Streptococcus salivarius is part of a tetracistronic operon encoding a phosphoenolpyruvate:mannose/glucose phosphotransferase system. Microbiology 146, 677-685.
Martin-Verstraete, I., Débarbouillé, M., Klier, A. & Rapoport, G.(1990). Levanase operon of Bacillus subtilis includes a fructose-specific phosphotransferase system regulating the expression of the operon. J Mol Biol 214, 657-671.[Medline]
Postma, P.(1977). Galactose transport in Salmonella typhimurium. J Bacteriol 129, 630-639.[Medline]
Postma, P. W., Lengeler, J. W. & Jacobson, G. R.(1993). Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria. Microbiol Rev 57, 543-594.[Abstract]
Reizer, J., Novotny, M. J., Hengstenberg, W. & Saier, M. H.Jr(1984). Properties of ATP-dependent protein kinase from Streptococcus pyogenes that phosphorylates a seryl-residue in HPr, a phosphocarrier protein of the phosphotransferase system. J Bacteriol 160, 333-340.[Medline]
Reizer, J., Hoischen, C., Titgemeyer, F., Rivolta, C., Rabus, R., Stülke, J., Karamat, D., Saier, M. H.Jr & Hillen, W.(1998). A novel protein kinase that controls carbon catabolite repression in bacteria. Mol Microbiol 27, 1157-1169.[Medline]
Stülke, J. & Hillen, W.(1999). Carbon catabolite repression in bacteria. Curr Opin Microbiol 2, 195-201.[Medline]
Thompson, J. & Chassy, B. M.(1985). Intracellular phosphorylation of glucose analogs via the phosphoenolpyruvate:mannose phosphotransferase system in Streptococcus lactis. J Bacteriol 162, 224-234.[Medline]
Vadeboncoeur, C. & Gauthier, L.(1987). The phosphoenolpyruvate:sugar phosphotransferase system of Streptococcus salivarius: identification of IIIMan protein. Can J Microbiol 33, 118-122.[Medline]
Vadeboncoeur, C. & Pelletier, M.(1997). The phosphoenolpyruvate phosphotransferase system of oral streptococci and its role in the control of sugar metabolism. FEMS Microbiol Rev 19, 187-207.[Medline]
Veyrat, A., Monedero, V. & Pérez-Martinez, G. (1994). Glucose transport by the phosphoenolpyruvate:mannose phosphotransferase system in Lactobacillus casei ATCC 393 and its role in carbon catabolite repression. Microbiology 140, 1141-1149.[Abstract]
Veyrat, A., Gosalbes, M. J. & Pérez-Martinez, G. (1996). Lactobacillus curvatus has a glucose transport system homologous to the mannose family of phosphoenolpyruvate-dependent phosphotransferase systems. Microbiology 142, 3469-3477.[Abstract]
Wehmeier, U. F., Wöhrl, B. M. & Lengeler, J. W.(1995). Molecular analysis of the phosphoenolpyruvate-dependent L-sorbose phosphotransferase system for Klebsiella pneumoniae and of its multidomain structure. Mol Gen Genet 246, 610-618.[Medline]
Received 30 August 2000;
revised 21 December 2000;
accepted 22 December 2000.