1 Department of Biomedical Sciences, University of South Alabama, Mobile, AL 36688, USA
2 Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham B15 2TT, UK
Correspondence
Michael P. Spector
mspector{at}usouthal.edu
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
One of the most common stresses encountered by S. Typhimurium, and many other bacteria, outside the confines of the laboratory is starvation for a carbon/energy source (C-source). S. Typhimurium, as well as other non-spore-forming bacteria, responds to carbon/energy starvation (C-starvation) with global alterations in gene expression, morphology and physiology. This response is known as the starvation-stress response (SSR) (Spector & Cubitt, 1992; Seymour et al., 1996
; Spector, 1998
; Spector et al., 1999b
). The SSR serves two functions: (1) to combat the long-term effects of C-starvation, and (2) to generate cross-resistance to other environmental stresses. The SSR includes aspects of: (a) avoidance, involving the production of new or higher-affinity C-source-utilization systems in an attempt to scavenge any utilizable C-sources from the environment; and (b) starvation/stress survival if an alternative C-source remains unavailable, ultimately generating a more efficient and hardy cell (Spector, 1998
).
The SSR genes identified thus far are under the control of one or more of three sigma factors, 70,
S and
E (O'Neal et al., 1994
; Spector et al., 1999a
; Kenyon et al., 2002
). The alternative sigma factor
S is encoded by the rpoS gene (Tanaka et al., 1993
). During the SSR,
S is induced early in the response to C-starvation in both Salmonella and Escherichia coli (W. J. Kenyon & M. P. Spector, unpublished data; Fang et al., 1992
; Tanaka et al., 1993
), and during the shift from glucose to lactose utilization in E. coli (Fischer et al., 1998
). Glucose is the carbon source of choice for Salmonella and many other bacteria. While Salmonella is growing on glucose, the uptake and utilization of other carbon sources are inhibited, in part as a result of catabolite repression and/or inducer exclusion (Notley & Ferenci, 1995
; Moat et al., 2002
). Glucose exhaustion results in a shift to utilize alternative C-sources present in the growth medium. In E. coli, a shift from glucose to lactose utilization causes growth to transiently halt, producing what is called a diauxic lag period. During diauxie, functions needed for lactose utilization are induced, allowing the cell to resume growth. In addition,
S and
S-dependent genes are induced during this diauxic lag period (Fischer et al., 1998
).
The alternative sigma factor E (encoded by the rpoE gene) is activated by certain stresses to the cell envelope that lead to the accumulation of denatured/unfolded proteins (Mecsas et al., 1993
, 1995
; Missiakas et al., 1996
; Jones et al., 1997
; Alba et al., 2002
). Previous studies indicate that, once activated,
E initiates the transcription of several genes with extracytoplasmic functions required for the cell envelope to combat the effects of the stress. In the absence of stress,
E is normally bound to the inner-membrane (IM) protein RseA, an anti-sigma factor or inhibitor of
E, preventing its interaction with RNA polymerase, and thus the transcription of
E-dependent genes (De Las Penas et al., 1997
; Missiakas et al., 1997
; Alba et al., 2002
, Miticka et al., 2003
). When a specific stress occurs to the cell envelope, RseA is degraded by DegS and YaeL,
E is then released and is able to bind to core RNA polymerase (E). E
E then directs the transcription of its dependent genes, many of which possess extracytoplasmic functions. A number of
E-regulated genes identified in E. coli encode cell-envelope-associated proteins that act on misfolded proteins, leading to their degradation, proper refolding or correct insertion into the outer membrane (OM), e.g. periplasmic (PP) proteases, peptidyl-prolyl isomerases and molecular chaperones (Erickson & Gross, 1989
; Danese & Silhavy, 1997
; Dartigalongue et al., 2001
; Alba et al., 2002
).
Previous findings in our laboratory (Kenyon et al., 2002) showed that
E activity and protein levels increase during the initial 45 h of C-starvation, and reach peak levels at around 4872 h of C-starvation. This suggests that C-starvation produces signals that lead to
E activation. Furthermore, rpoE mutants are defective in long-term C-starvation and C-starvation-inducible cross-resistance (Kenyon et al., 2002
), indicating that
E is an additional key regulator of the SSR. What is more,
E is critical for the virulence of S. Typhimurium in the mouse virulence model (Humphreys et al., 1999
).
In an effort to discern the role of the E regulon in the SSR, we examined its activity in the avoidance component of the SSR by measuring
E-dependent transcription during shifts from glucose to less-preferred but utilizable C-sources. Here we report that shifts to some but not all secondary C-sources tested resulted in a sustained increase in
E activity. The common feature of C-sources resulting in increased
E activity appears to be the induction of an OM-associated and/or PP-binding-protein component involved in its utilization. Based on our findings and apparent common features of these utilization systems, we hypothesized that one or more members of the
E regulon are needed for the adaptation of the cell envelope to growth on less-preferred but utilizable C-sources, specifically those C-sources with transport systems possessing extracytoplasmic solute receptors and/or OM proteins. Therefore,
E-regulated functions appear to play a role not only in the responses to certain environmental stresses, but also in the adaptation of Salmonella to new environmental conditions not typically associated with cell envelope stress.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Identification of a lamB : : MudJ (lac Kmr) -carrying strain from a library of C-starvation-inducible MudJ : : lac fusion (insertion) strains.
A lamB : : MudJ (lac Kmr) fusion-carrying strain was identified from our library of strains carrying MudJ (lac Kmr) insertions demonstrating C-starvation induction (Spector et al., 1988, 1999a
), using single-primer PCR, DNA sequence analysis and BLASTP search analysis as previously described (Spector et al., 1999a
, b
). The insertion of the MudJ : : lac in lamB was confirmed by the presence of the correct size PCR product using chromosomal DNA from ST55 as a template, a forward primer specific for the 3'-end of MudJ (PR18) and a reverse primer specific for the 3'-end of lamB (PR49).
Growth and E activation during C-source shifts.
For growth and E-activation analysis during glucose to alternative C-source shifts, overnight cultures of the desired strains were diluted 1 : 100 into fresh MS loC medium supplemented with one of the following: maltose, succinate, citrate, melibiose, D-trehalose, D-mannose, D-mannitol, D-fructose, glycerol, L-arabinose or D-galactose, all at a final concentration of 0·4 % (w/v), or no additional C-source (all C-sources were purchased from Sigma). The appropriate antibiotics were added as needed. The concentration of glucose in MS loC is the concentration used to produce C-starved cells (Spector & Cubitt, 1992
; O'Neal et al., 1994
; Kenyon et al., 2002
) and provides sufficient glucose to support growth for 34 generations before being exhausted. Therefore, growth can only continue if an alternative utilizable C-source is available in the growth medium. Growth was monitored spectrophotometrically by determining OD600 at pre-determined time intervals. Activation of
E was determined by measuring
-galactosidase activity as a reporter of promoter activity from plasmid pTF-p2; in addition,
-galactosidase activity driven by a rpoE-independent promoter (pTF-p1) was measured as a control (Kenyon et al., 2002
).
-Galactosidase activity was assayed by the method of Miller (1992)
and is expressed in Miller units. The results presented represent the mean±SEM from at least three separate experiments.
Generation of the lamB deletion mutant.
The -Red mutagenesis system provides a more efficient way of disrupting and deleting chromosomal genes, allowing the characterization of a gene's function (Datsenko & Wanner, 2000
), using the precise insertion of a selected antibiotic-resistance cassette into the gene of interest accompanied by a selected deletion. Using a slightly modified protocol and S. Typhimurium strain ST276 (carrying pKD46, a plasmid with the
-Red recombination enzymes under the control of the L-arabinose-inducible ParaBAD promoter; Table 1
), we constructed a defined deletion of the lamB gene from the S. Typhimurium chromosome, replacing it with an
-Kmr cassette.
Following the protocol of Datsenko & Wanner (2000), a PCR product was generated containing the Kmr cassette from pKD4 and sequence from the flanking region of the lamB gene of S. Typhimurium. PCR primers PR122 and PR123 (Table 1
) were designed to contain a 40 bp sequence homologous to lamB DNA, and a sequence corresponding to the P1 and P2 sites on pKD4. PCR reactions using these primers, PCR SuperMix High Fidelity (Invitrogen) and pKD4 as a template were run in an Ericomp Thermal Cycler. The size of the PCR product (approximately 1·6 kb) was confirmed by agarose gel electrophoresis, and the DNA was cleaned using the Promega Wizard PCR Prep Kit. The DNA was then digested with DpnI (Promega) for 3 h at 37 °C, and cleaned using the Promega Wizard DNA Clean-up Kit.
Electrocompetent cells of strain ST276 were prepared by growing an overnight culture of ST276 in 1 ml LB-Ap with shaking at 37 °C. The following morning, the overnight culture was diluted 1 : 100 into 25 ml of LB containing 1 mM L-arabinose, and grown to an OD600 of between 0·6 and 0·8. Freshly grown cells were pelleted, washed twice with 10 ml ice-cold sterile distilled water, and once with 10 ml ice-cold sterile 10 % (v/v) glycerol.
DpnI-digested DNA was then electroporated into the freshly prepared electrocompetent cells using an E. coli Pulsar electroporation unit and the protocol provided by the manufacturer (Bio-Rad). The cells were plated onto LB-Km agar and incubated overnight at 37 °C. Km-resistant colonies were then streaked for isolation onto LB-Km agar, and DNA was isolated from LB-Km overnight cultures using the Promega Genomic DNA Purification Kit. The presence of the desired mutation was confirmed by PCR analysis using primers PR48 and PR49 (Table 1) specific for the lamB sequence outside of the deletion site.
Construction of plasmid pKS34 carrying lamB under the control of an arabinose-inducible promoter, ParaBAD : : lamB.
Chromosomal DNA isolated from S. Typhimurium SL1344 (Wizard Genomic DNA Purification Kit; Promega) served as template for high-fidelity PCR amplification (Platinum PCR SuperMix High Fidelity; Invitrogen) of the lamB gene using the forward primer PR48 and the reverse primer PR49 (Table 1). The 1·4 kb PCR product was purified and ligated into pGEM-T Easy (Promega), and E. coli JM109 competent cells (Promega) were transformed with this, following the manufacturer's protocols. Plasmid minipreps (Wizard Plus Minipreps; Promega) from the ampicillin-resistant transformants were screened by PCR using primers PR48 and PR29 (Table 1
) to determine that the insert was oriented in the same direction as the lacZ gene in order to facilitate cloning into pBAD33. The subsequent plasmid was designated pKS33.
Digestion of pKS33 with SacI and SphI yielded a 1·5 kb fragment carrying the lamB gene. This fragment was isolated using agarose gel electrophoresis, extracted (Freeze 'N Squeeze columns; Bio-Rad) and cleaned (Wizard DNA Clean-Up System; Promega). It was then ligated with SacI/SphI-digested pBAD33 (a generous gift from Dr Jon Beckwith, Harvard University, Boston, MA, USA), and E. coli JM109 cells (Promega) were transformed with it and plated onto LB-Cm plates. Plasmid minipreps (Wizard Plus Minipreps; Promega) from transformant colonies were screened for the lamB insert by digestion with SacI and SphI, and agarose gel electrophoresis. The resultant plasmid was designated pKS34.
Overexpression of LamB and E activation.
To measure the effect of LamB overproduction on E activation as measured from a
E-dependent promoter in pTF-p2 we transformed SMS760 (SL1344/pTF-p2) with pKS34 to produce strain SMS908 (Table 1
). The desired strains were grown overnight in LB plus the appropriate antibiotic. Overnight cultures were then diluted 1 : 100 into fresh LB broth with the appropriate antibiotic(s), and grown to mid-exponential phase before being divided into six separate cultures to which 0, 25, 50, 100, 200 or 400 µM L-arabinose was added. Cultures were then incubated for an additional 1 h at 37 °C with aeration, at which point
-galactosidase activity was assayed using the method of Miller (1992)
.
![]() |
RESULTS AND DISCCUSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Fig. 1(a) illustrates the typical increase in
E activity (as determined by increased
-galactosidase expression driven by an
E-dependent promoter) observed during C-starvation (Kenyon et al., 2002
), and is included for comparison purposes. Shifts from glucose to maltose, citrate or succinate all produced discernible, yet transient, diauxic lag periods, and more importantly sustained increases in
E activity (Fig. 1bd
) comparable to C-starved cells (Fig. 1a
) over the same time period. In contrast, shifts from glucose to maltose, citrate, succinate or any other alternative C-source tested, as well as C-starvation, produced relatively constant
-galactosidase activity [2478±69 (SEM) Miller units] over the same time period from the
E-independent (
70-dependent) promoter in pTF-p1.
|
The scenario for succinate utilization in S. Typhimurium is more complicated. The homologues of the dctPQM genes encoding the aerobic dicarboxylate-transporter system DctPQM in Rhodobacter capsulatus (Rabus et al., 1999; Janausch et al., 2002
) are apparently absent from the S. Typhimurium genome (McClelland et al., 2001
). However, there are at least three hypothetical genes encoding putative extracytoplasmic solute receptors for C4-dicarboxylates that may play a role in succinate utilization (STM3169, GenBank accession number AE008845,1775618746; yiaO, accession number AE008870, 963710623; STM4054, accession number AE008889, complement 1023311216). Of these three, YiaO along with YiaM/YiaN, and STM4054 along with STM4052/STM4053 may constitute tripartite ATP-independent periplasmic- (TRAP) transporter systems involved in succinate utilization (Rabus et al., 1999
; Janausch et al., 2002
). In addition, S. Typhimurium possesses the genes for two other C4-dicarboxylate-transport systems: (1) the anaerobic Dcu dicarboxylate-transporter system, which appears to be involved in fumarate respiration rather than C4-dicarboxylate utilization and as part of this function actually results in succinate efflux from the cytoplasm (Janausch et al., 2002
), and (2) a homologue of the DctA H+/Na+ : C4-dicarboxylate/dicarboxylic amino acid symporter, which was found to be a major C4-dicarboxylate transporter during aerobic growth in E. coli. Mutants of dctA in E. coli grow very poorly or not at all on succinate and other C4-dicarboxylates (Davies et al., 1999
). However, its cognate extracytoplasmic solute receptor (i.e. succinate-binding protein) has not been definitively identified. In E. coli, the cbt gene was proposed as the putative C4-dicarboxylate-binding protein possibly as part of an OM porin (Lo, 1977
; Lo & Bewick, 1981
). Whether this complex is expressed under the conditions tested in this study has not been demonstrated, but recent evidence suggests that cbt may be an allele of the ferric-enterobactin-transport component gene fepA, which is iron regulated (Braun & Braun, 2002
) in both E. coli and Salmonella. Thus, the involvement of PP and/or OM component(s) in succinate utilization in S. Typhimurium, although likely, is ambiguous and clearly complicated.
Shifts from glucose to the PEP : PTS-dependent sugars trehalose, mannose, mannitol or fructose do not result in a sustained increase in E activity
Many sugars are translocated into the cell by the phosphoenolpyruvate (PEP) : sugar phosphotransferase system (PTS) (Postma et al., 1993). The utilization of secondary PTS sugars, and some other non-PTS sugars, is catabolite repressed and/or subject to inducer exclusion during growth on glucose. This is in part a result of low intracellular levels of the signal nucleotide cyclic AMP (cAMP) caused by greatly reduced adenylate cyclase activity, resulting from greatly reduced levels of the phosphorylated Enzyme IIA component of the glucose-specific PTS (P
EnzIIAgluc). The exhaustion of glucose leads to accumulation of P
Enz IIAgluc and the activation of adenylate cyclase. The resulting increased cAMP levels, and in some cases the presence of the C-source (or a derivative), induces the expression of the utilization enzymes for the secondary C-source. For some of these C-sources, this involves the production of specific Enzyme IIA and IIB components for its PTS. The IIB component for these PTS sugars is an IM protein, while their IIA component is associated with the cytoplasmic side of the IM; however, there are no PP or OM components involved in the PTS. We therefore wanted to determine if shifts from glucose to known PTS sugars might also generate signals leading to sustained
E activation.
In contrast to maltose, citrate and succinate, a shift from glucose to the PTS-dependent sugars trehalose (Fig. 2a), fructose (Fig. 2b
), mannose or mannitol (data not shown) did not lead to a discernible diauxic lag period or sustained
E activation. Results for mannose and mannitol were very similar to that of fructose. These results indicate that a shift from glucose to a secondary C-source, in general, is insufficient to cause sustained
E activation. It also demonstrated more specifically that shifts from glucose to PTS sugars do not generate signals leading to sustained
E activation, thus supporting our hypothesis, given that their utilization does not involve PP and/or OM components.
|
Neither shifts from glucose to melibiose (Fig. 3a), L-arabinose (Fig. 3b
), D-galactose, nor glycerol (data not shown) resulted in a sustained increase in
E activity; although there was a transient increase in some cases. The results for D-galactose and glycerol were very similar to the result for L-arabinose. Interestingly, the shift from glucose to melibiose produced an observable transitory diauxic lag period, but again this was not accompanied by a sustained elevation in
E activity (Fig. 3a
). These latter findings suggest that it is not the occurrence of a diauxic lag period that results in signals leading to a sustained rise in
E activity.
|
In both E. coli and S. Typhimurium, D-galactose can be transported into the cell through the galactose-specific galactose permease GalP or the binding-protein-dependent methyl-galactoside Mgl system (Postma, 1977; Muller et al., 1985
; Benner-Luger & Boos, 1988
). The mglB-encoded protein is a PP-binding protein that can bind to galactose as well as other sugars, e.g. fucose. Although this might appear contradictory to our hypothesis, galactose only slightly induces the mgl genes in a galP+ strain background (Postma, 1977
; Muller et al., 1985
; Benner-Luger & Boos, 1988
). Thus, the MglB protein is not induced significantly under our experimental conditions. So, the lack of a sustained increase in
E activity during a glucose to D-galactose shift can still be explained in the context of our hypothesis. The pertinent characteristics for all the secondary C-sources tested are summarized in Table 2
.
|
We targeted the lamB gene for several reasons. First, it is not essential for the utilization of maltose, yet it is induced during shifts from glucose to maltose (discussed above). Second, a lamB : : -Km mutant strain (SMS871) exhibits virtually identical growth, compared to the wild-type parent strain, during glucose to maltose shifts (Fig. 4a
). Furthermore, the situation for citrate or succinate utilization is problematic for this study. Mutants of tctC, lacking the extracytoplasmic tricarboxylate-binding-protein/receptor component, are defective in citrate utilization (Winnen et al., 2003
), and thus may mimic conditions of C-starvation. What's more, succinate utilization in Salmonella is not very well characterized. There are at least three putative C4-dicarboxylate-binding proteins in the S. Typhimurium genome (McClelland et al., 2001
), and the presence of C4-dicarboxylate PP- and/or OM-utilization components in S. Typhimurium as well as E. coli still requires clarification. Deletion of one or more of the C4-dicarboxyate PP-binding proteins is likely to make the cells defective in succinate utilization similar to the scenario for citrate utilization.
|
Overproduction of LamB protein in the absence of glucose starvation or a glucose to maltose shift increases activation of E
To further demonstrate that up-regulated expression of LamB directly results in increased E activity, we overproduced LamB from the arabinose-inducible araBAD promoter in pBAD33 (Guzman et al., 1995
). As shown in Fig. 5
, increased
E activity was observed when we artificially overproduced LamB from an arabinose-inducible promoter (SMS908) in the absence of glucose starvation or during a glucose to maltose shift (Fig. 5b
). An increase in
E activity was not observed under these conditions in a strain lacking the pKS34 plasmid (SMS760), indicating that it is the overproduction of LamB and not the addition of arabinose itself that results in increased
E activity. Furthermore, the increased levels of
-galactosidase activity observed with rising concentrations of arabinose in SMS908 (Fig. 5b
) required a functional
E protein, since in similar experiments with the rpoE : :
-Kmr mutant SMS909 low but constant
-galactosidase activities (approximately 10 Miller units), equivalent to a strain carrying the pRS1274 vector alone, were detected.
|
A question arises as to what E-regulated functions might be involved in this adaptation process. We are currently searching for these functions. We do not believe them to be either DegP, FkpA or SurA since we have found that in S. Typhimurium they are not regulated by
E (or C-starvation) under the conditions tested here (W. J. Kenyon, A. Stevenson, S. Humphreys, M. Roberts & M. P. Spector, unpublished data). Thus, some alternative protease(s), chaperone(s), peptidyl-prolyl isomerase(s) or other function(s) as yet unidentified, would appear to be involved in the adaptation of the cell envelope to C-starvation conditions.
Studies in E. coli (Ades et al., 2003) identified trends in
E activity occurring before, during and after the inducing stress of high temperature. During the initiation of the stress response,
E activity is elevated. The activity remains elevated during the adaptation phase while the cell adapts to the stress. When the stress is removed,
E activity drops below that seen in normal conditions, and then slowly rises to pre-stress levels. A similar scenario can be postulated for shifts from glucose to maltose, for example, which even though not typically considered a stress do require the cells to adapt to the change in growth conditions. Interestingly, during C-starvation
E levels are seen to continue to rise over a 4872 h period before levelling off (Kenyon et al., 2002
).
Conclusions
We report here that shifts from glucose to maltose, citrate or succinate, but not trehalose, mannose, mannitol, fructose, glycerol, L-arabinose, galactose or melibiose, result in a sustained elevation of E activity. The common feature of maltose, citrate and succinate utilization is the production of extracytoplasmic (PP) solute-receptors/binding proteins (e.g. TctC) and/or OM transport proteins or porins (e.g. LamB). The other secondary C-sources tested required either PEP : PTS-dependent-transport systems (e.g. trehalose, mannose, mannitol and fructose) or non-PTS IM-transport systems (e.g. glycerol, L-arabinose, galactose and melibiose). However, an extracytoplasmic component in their utilization systems is either absent, unknown or not expressed under the conditions tested in S. Typhimurium. The findings presented here support the hypothesis that
E-regulated functions are needed for the adaptation of cells to new environmental conditions that necessitate changes in the extracytoplasmic compartment of the cell, i.e. OM or periplasm. This implies that members of the
E regulon have functions beyond the repair or elimination of damaged extracytoplasmic proteins resulting from an environmental stress.
![]() |
ACKNOWLEDGEMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Ades, S. E., Grigorova, I. L. & Gross, C. A. (2003). Regulation of the alternative sigma factor E during initiation, adaptation, and shutoff of the extracytoplasmic heat shock response in Escherichia coli. J Bacteriol 185, 25122519.
Alba, B. M., Leeds, J. A., Onufryk, C., Lu, C. Z. & Gross, C. A. (2002). DegS and YaeL participate sequentially in the cleavage of RseA to activate the E-dependent extracytoplasmic stress response. Genes Dev 16, 21562168.
Benner-Luger, D. & Boos, W. (1988). The mglB sequence of Salmonella typhimurium LT-2; promoter analysis by gene fusions and evidence for a divergently oriented gene coding for the mgl repressor. Mol Gen Genet 214, 579587.[CrossRef][Medline]
Betton, J. M., Sassoon, N., Hofnung, M. & Laurent, M. (1998). Degradation versus aggregation of misfolded maltose-binding protein in the periplasm of Escherichia coli. J Biol Chem 273, 88978902.
Braun, V. & Braun, M. (2002). Iron transport and signaling in Escherichia coli. FEBS Lett 529, 7885.[CrossRef][Medline]
Chan, R. K., Botstein, D., Watanabe, T. & Ogata, Y. (1972). Specialized transduction of tetracycline resistance by phage P22 in Salmonella typhimurium. II. Properties of a high-frequency-transducing lysate. Virology 50, 883898.[CrossRef][Medline]
Danese, P. N. & Silhavy, T. J. (1997). The E and the Cpx signal transduction systems control the synthesis of periplasmic protein-folding enzymes in Escherichia coli. Genes Dev 11, 11831193.[Abstract]
Dartigalongue, C., Missiakas, D. & Raina, S. (2001). Characterization of the Escherichia coli E regulon. J Biol Chem 276, 2086620875.
Datsenko, K. A. & Wanner, B. L. (2000). One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products. Proc Natl Acad Sci U S A 97, 66406645.
Davies, S. J., Golby, P., Omrani, D., Broad, S. A., Harrington, V. L., Guest, J. R., Kelly, D. J. & Andrews, S. C. (1999). Inactivation and regulation of the aerobic C4-dicarboxylate transport (dctA) gene of Escherichia coli. J Bacteriol 181, 56245635.
De Las Penas, A., Connelly, L. & Gross, C. A. (1997). The E-mediated response to extracytoplasmic stress in Escherichia coli is transduced by RseA and RseB, two negative regulators of
E. Mol Microbiol 24, 373385.[CrossRef][Medline]
Erickson, J. W. & Gross, C. A. (1989). Identification of the E subunit of Escherichia coli RNA polymerase: a second alternate sigma factor involved in high-temperature gene expression. Genes Dev 3, 14621471.[Abstract]
Fang, F. C., Libby, S. J., Buchmeier, N. A., Loewen, P. C., Switala, J., Harwood, J. & Guiney, D. G. (1992). The alternative factor KatF (RpoS) regulates Salmonella virulence. Proc Natl Acad Sci USA 89, 1197811982.
Fischer, D., Teich, A., Neubauer, P. & Hengge-Aronis, R. (1998). The general stress sigma factor S of Escherichia coli is induced during diauxic shift from glucose to lactose. J Bacteriol 180, 32033206.
Guzman, L.-M., Belin, D., Carson, M. J. & Beckwith, J. (1995). Tight regulation, modulation, and high-level expression by vectors containing the arabinose PBAD promoter. J Bacteriol 177, 41214130.
Hall, J. A., Gehring, K. & Nikaido, H. (1997). Two modes of ligand binding in maltose-binding protein of Escherichia coli. Correlation with the structure of ligands and the structure of binding protein. J Biol Chem 272, 1760517609.
Horazdovsky, B. F. & Hogg, R. W. (1989). Genetic reconstitution of the high-affinity L-arabinose transport system. J Bacteriol 171, 30533059.[Medline]
Hoseith, S. K. & Stocker, B. A. D. (1981). Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines. Nature 291, 238239.[CrossRef][Medline]
Humphreys, S., Stevenson, A., Bacon, A., Weinhardt, A. B. & Roberts, M. (1999). The alternative sigma factor, E, is critically important for the virulence of Salmonella Typhimurium. Infect Immun 67, 15601568.
Humphreys, S., Rowley, G., Stevenson, A., Kenyon, W. J., Spector, M. P. & Roberts, M. (2003). The role of periplasmic peptidyl-prolyl-isomerases in Salmonella virulence. Infect Immun 71, 53865388.
Janausch, I. G., Zientz, E., Tran, Q. H., Kröger, A. & Unden, G. (2002). C4-dicarboxylate carriers and sensors in bacteria. Biochim Biophys Acta 1553, 3956.[CrossRef][Medline]
Jones, C. H., Danese, P. N., Pinkner, J. S., Silhavy, T. J. & Hultgren, S. J. (1997). The chaperone-assisted membrane release and folding pathway is sensed by two signal transduction systems. EMBO J 16, 63946406.
Kehres, D. G. & Hogg, R. W. (1992). Escherichia coli K-12 arabinose-binding protein mutants with altered transport properties. Protein Sci 1, 16521660.
Kenyon, W. J., Sayers, D. G., Humphreys, S., Roberts, M. & Spector, M. P. (2002). The starvation-stress response of Salmonella enterica serovar Typhimurium requires E, but not CpxR-regulated extracytoplasmic functions. Microbiology 148, 113122.[Medline]
Lawhon, S. D., Frye, J. G., Suyemoto, M., Porwollik, S., McClelland, M. & Altier, C. (2003). Global regulation by CsrA in Salmonella typhimurium. Mol Microbiol 48, 16331645.[CrossRef][Medline]
Lo, T. C. (1977). The molecular mechanism of dicarboxylic acid transport in Escherichia coli K-12. J Supramol Struct 7, 463480.[CrossRef][Medline]
Lo, T. C. & Bewick, M. A. (1981). Use of a nonpenetrating substrate analogue to study the molecular mechanism of the outer membrane dicarboxylate transport system in Escherichia coli K-12. J Biol Chem 256, 55115517.
Maloy, S. R. (1990). Experimental Techniques in Bacterial Genetics. Boston, MA: Jones & Bartlett.
McClelland, M., Sanderson, K. E., Spieth, J. & 23 other authors (2001). Complete genome sequence of Salmonella enterica serovar Typhimurium LT2. Nature 413, 852856.[CrossRef][Medline]
Mecsas, J., Rouviere, P. E., Erickson, J. W., Donohue, T. J. & Gross, C. A. (1993). The activity of E, an Escherichia coli heat-inducible
-factor, is modulated by expression of outer membrane proteins. Genes Dev 7, 26182628.[Abstract]
Mecsas, J., Welch, R., Erickson, J. W. & Gross, C. A. (1995). Identification and characterization of an outer membrane protein, OmpX, in Escherichia coli that is homologous to a family of outer membrane proteins including Ail of Yersinia enterocolitica. J Bacteriol 177, 799804.
Miller, J. H. (1992). A Short Course in Bacterial Genetics: a Laboratory Manual and Handbook for Escherichia coli and Related Bacteria. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.
Missiakas, D., Betton, J. M. & Raina, S. (1996). New components of protein folding in extracytoplasmic compartments of Escherichia coli SurA, FkpA and Skp/OmpH. Mol Microbiol 21, 871884.[CrossRef][Medline]
Missiakas, D., Mayer, M. P., Lemaire, M., Georgopoulos, C. & Raina, S. (1997). Modulation of the Escherichia coli E (RpoE) heat-shock transcription-factor activity by the RseA, RseB and RseC proteins. Mol Microbiol 24, 355371.[CrossRef][Medline]
Miticka, H., Rowley, G., Rezuchova, B., Homerova, D., Humphreys, S., Farn, J., Roberts, M. & Kormanec, J. (2003). Transcriptional analysis of the rpoE gene encoding extracytoplasmic stress response sigma factor sigma E in Salmonella enterica serovar Typhimurium. FEMS Microbiol Lett 226, 307314.[CrossRef][Medline]
Moat, A. G., Foster, J. W. & Spector, M. P. (2002). Microbial Physiology, 4th edn. New York: Wiley-Liss.
Muller, N., Heine, H. G. & Boos, W. (1985). Characterization of the Salmonella typhimurium mgl operon and its gene products. J Bacteriol 163, 3745.[Medline]
Neidhardt, F. C., Bloch, P. L. & Smith, D. F. (1974). Culture medium for enterobacteria. J Bacteriol 119, 736747.[Medline]
Notley, L. & Ferenci, T. (1995). Differential expression of mal genes under cAMP and endogenous inducer control in nutrient-stressed Escherichia coli. Mol Microbiol 16, 121129.[Medline]
O'Neal, C. R., Gabriel, W. M., Turk, A. K., Libby, S. J., Fang, F. C. & Spector, M. P. (1994). RpoS is necessary for both positive and negative regulation of starvation-survival genes during phosphate, carbon, and nitrogen starvation in Salmonella typhimurium. J Bacteriol 176, 46104616.[Abstract]
Ponting, C. P. (1997). Evidence for PDZ domains in bacteria, yeast, and plants. Protein Sci 6, 464468.
Postma, P. W. (1977). Galactose transport in Salmonella typhimurium. J Bacteriol 129, 630639.[Medline]
Postma, P. W., Lengeler, J. W. & Jacobson, G. R. (1993). Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria. Microbiol Rev 57, 543594.[Medline]
Rabus, R., Jack, D. L., Kelly, D. J. & Saier, M. H., Jr (1999). TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters. Microbiology 145, 34313445.[Medline]
Schulein, K. & Benz, R. (1990). LamB (maltoporin) of Salmonella typhimurium: isolation, purification and comparison of sugar binding with LamB of Escherichia coli. Mol Microbiol 4, 625632.[Medline]
Seymour, R. L., Mishra, P. V., Khan, M. A. & Spector, M. P. (1996). Essential roles of core starvation-stress response loci in carbon-starvation-inducible cross-resistance and hydrogen peroxide-inducible adaptive resistance to oxidative challenge in Salmonella typhimurium. Mol Microbiol 20, 497505.[CrossRef][Medline]
Simons, R. W., Houman, F. & Kleckner, N. (1987). Improved single and multi-copy lac-based cloning vectors for protein and operon fusions. Gene 53, 8596.[CrossRef][Medline]
Songyang, Z., Fanningm, A. S., Fu, C. & 7 other authors (1997). Recognition of unique carboxyl-terminal motifs by distinct PDZ domains. Science 275, 7377.
Spector, M. P. (1998). The starvation-stress response (SSR) of Salmonella. Adv Microb Physiol 40, 235279.
Spector, M. P. & Cubitt, C. L. (1992). Starvation-inducible loci of Salmonella typhimurium, regulation and roles in starvation survival. Mol Microbiol 6, 14671476.[Medline]
Spector, M. P., Park, Y. K., Tirgari, S., Gonzalez, T. & Foster, J. W. (1988). Identification and characterization of starvation-regulated genetic loci in Salmonella typhimurium by using Mu d-directed lacZ operon fusion. J Bacteriol 170, 345351.[Medline]
Spector, M. P., DiRusso, C. C., Pallen, M. J., Garcia del Portillo, F., Dougan, G. & Finlay, B. B. (1999a). The medium-/long-chain fatty acyl-CoA dehydrogenase (fadF) gene of Salmonella typhimurium is a phase 1 starvation-stress response (SSR) locus. Microbiology 145, 1531.[Medline]
Spector, M. P., Garcia del Portillo, F., Bearson, S. M., Mahmud, A., Magut, M., Finlay, B. B., Dougan, G., Foster, J. W. & Pallen, M. J. (1999b). The rpoS-dependent starvation-stress response locus stiA encodes a nitrate reductase (narZYWV) required for carbon-starvation-inducible thermotolerance and acid tolerance in Salmonella typhimurium. Microbiology 145, 30353045.[Medline]
Tanaka, K., Takayanagi, Y., Fujita, N., Ishihama, A. & Takahashi, H. (1993). Heterogeneity of the principal factor in Escherichia coli: the rpoS gene product,
38, is a second principal factor of RNA polymerase in stationary-phase Escherichia coli. Proc Natl Acad Sci U S A 90, 35113515.
Testerman, T. L., Vasquez-Torres, A., Xu, Y., Jones-Carson, J., Libby, S. J. & Fang, F. C. (2002). The alternative sigma factor E controls antioxidant defences required for Salmonella virulence and stationary-phase survival. Mol Microbiol 43, 771782.[CrossRef][Medline]
Walsh, N. P., Alba, B. M., Bose, B., Gross, C. A. & Sauer, R. T. (2003). OMP peptide signals initiate the envelope-stress response by activating DegS protease via relief of inhibition mediated by its PDZ domain. Cell 113, 6171.[CrossRef][Medline]
Winnen, B., Hvorup, R. N. & Saier, M. H., Jr (2003). The tripartite tricarboxylate transporter (TTT) family. Res Microbiol 154, 457465.[CrossRef][Medline]
Widenhorn, K. A., Somers, J. M. & Kay, W. W. (1988). Expression of the divergent tricarboxylate transport operon (tctI) of Salmonella typhimurium. J Bacteriol 170, 32233227.[Medline]
Received 22 September 2004;
revised 1 April 2005;
accepted 4 April 2005.
HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
INT J SYST EVOL MICROBIOL | MICROBIOLOGY | J GEN VIROL |
J MED MICROBIOL | ALL SGM JOURNALS |