Glycogen production by different Salmonella enterica serotypes: contribution of functional glgC to virulence, intestinal colonization and environmental survival

Alisdair McMeechan1, Margaret A. Lovell2, Tristan A. Cogan1, Kerrie L. Marston2, Tom J. Humphrey1 and Paul A. Barrow2,{dagger}

1 School of Clinical Veterinary Science, University of Bristol, Langford House, Langford, Bristol BS40 5DU, UK
2 Institute for Animal Health (IAH), Compton Laboratory, Compton, Newbury, Berkshire RG20 7NN, UK

Correspondence
Paul A. Barrow
Paul.Barrow{at}bbsrc.ac.uk


   ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
In enteric bacteria, the contribution of endogenous energy sources to survival both inside and outside the host is poorly understood. The contribution of glycogen production to the virulence, colonization and environmental survival of different Salmonella enterica serotypes was assessed. Of 19 serotypes (339 strains) tested for glycogen production, 17 (256 strains) were positive. The avian-specific serovars S. Gallinarum (62 strains) and S. Pullorum (21 strains) did not produce glycogen. The sequence of glgC in three S. Gallinarum strains tested revealed an identical deletion of 11 consecutive bases, which was not present in S. Pullorum, and a CCC insertion after position 597. Transduction of S. Gallinarum and S. Pullorum to a glycogen-positive phenotype did not change the ability to colonize the intestine or affect virulence in the chicken. Mortality rates in chickens following oral infection with a S. Typhimurium glycogen mutant (glgC : : km) were not significantly reduced, although colonization of the intestine was reduced over the first 4 weeks of the trial. Growth and yield of the glgC : : km mutant were comparable to the parent. The glgC mutant survived less well in faeces and in water at 4 °C when the strain was grown in LB broth containing 0·5 % glucose, and in saline it died off more rapidly after 7 days. The data suggest that glycogen has a complex but comparatively minor role in virulence and colonization, but a more significant role in survival.


Abbreviations: IAH, Institute for Animal Health; WT, wild-type

{dagger}Present address: School of Veterinary Science and Medicine, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK.


   INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
From the point of view of infection biology, Salmonella enterica can be divided into two broad groups (Parker & Collier, 1990). One group consists of a relatively small number of serotypes that typically produce typhoid-like systemic disease in a narrow range of host species. These include S. enterica serovars Typhi in man, Gallinarum in birds and Choleraesuis in pigs. In the absence of clinical disease, they colonize the gut poorly (Barrow et al., 1988; Parker & Collier, 1990), and therefore rarely enter the human food chain. The remaining more than 2000 serovars rarely produce systemic disease, but are able to colonize the alimentary tract of food animals asymptomatically.

For both types of Salmonella, the alimentary tract is a major niche. There is great flexibility and redundancy in the metabolic capacity in both Salmonella and Escherichia coli (Neidhardt, 1996); however, the relative role of different metabolic pathways is not well understood. In a recent study, colonization of the murine intestine was only affected by mutations in sugar pathways. Colonization was unaffected by mutation in genes involved in phospholipid and amino acid catabolism, gluconeogenesis, the tricarboxylic acid cycle or the pentose phosphate pathway (Chang et al., 2004).

Glycogen is a major energy storage compound in many bacteria, including S. Typhimurium (Steiner & Preiss, 1977), in addition to its importance in eukaryotes. It is a polysaccharide containing glucose units in a branched structure, comprising predominantly {alpha}-1,4 linkages and a smaller number of {alpha}-1,6 branching glucosyl linkages. It is produced predominantly under limiting growth conditions in which carbon sources such as glucose are present (Preiss, 1996).

The glycogen locus, both in E. coli and in S. Typhi and S. Typhimurium, consists of two adjacent operons transcribed unidirectionally, and encoding glgB (branching enzyme) and glgX (glycosyl hydrolase) in one operon, and glgC (ADP-glucose pyrophosphorylase), glgA (glycogen synthase) and glgP (glycogen phosphorylase) in the other (Preiss & Romeo, 1989; Preiss, 1996). The function of the products of these genes has been studied extensively in E. coli. The activities of GlgC, GlgA and GlgB increase in the presence of rich medium containing glucose, and expression also increases as the bacteria enter stationary phase (Preiss, 1984). Synthesis rates are also inversely proportional to growth rate when nutrients such as nitrogen are limited (Preiss, 1984). Under conditions of nutrient deficiency, glycogen accumulates, the amount depending on substrate availability and allosteric regulation by ADP-glucose pyrophosphorylase (Preiss, 1984). Expression of glgC and glgA is regulated by intracellular bacterial signals involved in denoting energy status. These include cAMP/CRP, CsrA and ppGpp (Romeo & Preiss, 1989; Romeo et al., 1993). In E. coli, CsrA binding to glgCAP transcripts inhibits glycogen metabolism by promoting glgCAP mRNA decay (Baker et al., 2002). Transcription of the glycogen operon is mediated through the major active form of RNA polymerase (E{sigma}70), and is subject to regulation by RpoS (Hengge-Aronis & Fischer, 1992). In addition, rpoS mutants of E. coli have been reported to accumulate less glycogen (Makinoshima et al., 2003). The regulation of glycogen biosynthesis and catabolism is therefore adjusted to accommodate changes in the availability of easily utilizable energy sources.

Given the widespread existence of glycogen in enteric genera, including Citrobacter, Enterobacter, Klebsiella, Serratia and Shigella (Preiss, 1984), it seems reasonable that, under conditions of nutritional and other stresses associated with infection and environmental survival, the accumulation of energy-storage compounds such as glycogen would be important. We therefore examined the contribution of glycogen production to virulence, intestinal colonization and survival. We observed that S. Gallinarum and S. Pullorum do not accumulate glycogen. The significance of this to the biology of these serovars was therefore assessed. Since GlgC catalyses the first committed and rate-limiting step in glycogen biosynthesis in bacteria (Jin et al., 2005), we constructed a defined mutant in glgC in S. Typhimurium.


   METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
Bacterial strains and plasmids.
Strains and plasmids used during this study are shown in Table 1. S. Typhimurium F98 produces systemic disease in young poultry and is able to colonize their alimentary tract (Barrow et al., 1987b, 1988). S. Gallinarum 9 produces typical fowl typhoid in poultry (Smith, 1955; Barrow et al., 1987a). S. Gallinarum 287/91, 21-92 and S. Pullorum strain 3 were isolated from diseased poultry. For intestinal colonization studies, mutants were used which were resistant to nalidixic acid. The NalR resistance determinant has previously been shown not to adversely affect growth, virulence or colonization (Barrow et al., 1987c; Zhang-Barber et al., 1997).


View this table:
[in this window]
[in a new window]
 
Table 1. Bacterial strains and plasmids

AmpR, ampicillin resistance; TetR, tetracycline resistance; CmR, chloramphenicol resistance; KanR, kanamycinresistance; Glc+, glycogen positive.

 
Growth media and conditions used.
The media used in this study were LB or M9 minimal medium (Sambrook & Russell, 1989) containing 0·5 % (w/v) glucose. Unless otherwise stated, cultures were grown overnight at 37 °C with shaking at 150 r.p.m. The following growth factors were added for S. Gallinarum and S. Pullorum: 2 µg thiamine ml–1, 100 µg nicotinic acid ml–1, and glutamic acid, arginine, proline, cysteine, leucine and hisitidine all at 20 µg ml–1. Phenylalanine, tryptophan, tyrosine, para-aminobenzoic acid and sodium dihydroxybenzoate, all at 100 µg ml–1, were added for the S. Typhi aroCaroD strain. Where mentioned, casamino acids (Merck) were added at 0·5 % (w/v).

Mutant construction.
The defined mutation in glgC was produced as previously described (Zhang-Barber et al., 1997; Turner et al., 1998). Fragments of the glgC gene were amplified from S. Typhimurium F98 DNA by PCR using the primer pairs Gly01-EcoRI (5'-TGAATTCGTGAGTTTAGAGAAGAACGA-3') and Gly02-KpnI (5'-CAATTCATACAGGTACCCATCACGCCGAACGCCGT-3'), and Gly03-KpnI (5'-ATGGGTACCTGTATGAATTGCTGG-3') and Gly04-XbaI (5'-CTCTAGACAGCATTTCACGCGTGACCA-3') (restriction sites are underlined). Selection for KmRCmS colonies indicated loss of the suicide vector and PCR confirmed the desired deletion.

Glycogen-positive (Glc+) transductants of S. Gallinarum and S. Pullorum were created as follows. A 485 bp fragment of the glpD gene, adjacent to the glycogen operon, was amplified from S. Enteritidis P125109 and cloned into pDM4. This construct was electroporated into E. coli S17.1 lambda pir, from which it was conjugated into S. Enteritidis P125109; a chloramphenicol-resistant mutant was then selected. This was confirmed by PCR to have resulted from the insertion of the construct into the glpD gene. P22 transduction was then used to transfer chloramphenicol resistance to S. Gallinarum 9 and S. Pullorum 3. A high proportion of the purified recipient colonies were found to produce glycogen. These colonies were checked for motility in soft agar to confirm that they were serovars of Gallinarum and Pullorum (non-motile), and not Enteritidis (motile).

Glycogen assay.
The production of glycogen was detected using a standard procedure involving iodine staining after growth on glucose-rich agar (Govons et al., 1969). Bacteria were grown on an agar medium comprising 0·1 % K2SO4, 1·3 % K2HPO4, 0·47 % KH2PO4, 0·01 % MgSO4.7H2O, 0·6 % yeast extract and 1·5 % Bacto agar (Difco). Filtered glucose was added at 1 % (w/v) after sterilization.

DNA sequence analysis.
From the published S. Typhimurium glgC sequence (GenBank X59281), primers were designed at intervals along the gene and used to amplify glgC from S. Gallinarum strains 9, 287/91 and 21-92, and S. Pullorum strain 3. The fragments were then cloned into pGEM-T Easy (Promega), and plasmid-specific primers were used as sequencing primers. DNA sequencing was carried out using a PRISM Ready Reaction DyeDeoxy Terminator Cycle Sequencing kit (Applied Biosystems, Inc.) and the Applied Biosystems 373 DNA sequencer. Nucleotide sequences were analysed by comparison with the published sequence for S. Typhi and S. Typhimurium (www.sanger.ac.uk/Projects/Salmonella/ and www.salmonella.org/).

Measurement of bacterial growth.
For each strain to be tested, triplicate cultures were diluted to between 103 and 104 c.f.u. ml–1 in M9 medium, and 300 µl was inoculated per well of a honeycomb microplate. Growth was measured using a Bioscreen C automatic turbidimetric analyser (Thermo Electron Corp., Basingstoke, UK). A higher inoculum (106–107 c.f.u. ml–1) was used for S. Gallinarum and S. Pullorum, since preliminary studies demonstrated poorer growth in M9, compared with that of S. Typhimurium.

Intestinal colonization.
Specific-pathogen-free chickens that were free of Salmonella and free of antibody against Salmonella enterica were used. Studies of intestinal colonization were carried out in two ways. In the first method, the spread of infection was observed by infecting three out of 20 four-day-old Light Sussex chickens with 0·3 ml containing 109 c.f.u. of the strain to be tested. At weekly intervals, cloacal swabs were taken (Smith & Tucker, 1975) and plated onto Brilliant Green agar (BGA) plates containing sodium nalidixate (20 µg ml–1) and novobiocin (1 µg ml–1). Bacteria that might be non-culturable by direct plating were enriched by incubating the swabs in selenite broth overnight at 37 °C, before plating on BGA, as before. In the second method, all 20 chickens were infected directly with the same inoculum level as that of the first method.

Virulence assays.
For virulence assays, Rhode Island Red chickens from the IAH flock were used. These have moderate susceptibility to systemic salmonellosis and were reared as described previously (Barrow et al., 1988). For infection with S. Typhimurium, day-old chicks were used, and for S. Gallinarum, three-week-olds were used. Groups of 20 chickens were inoculated orally into the crop with 3x108 c.f.u. of the strain to be tested in 100 µl. Animals were observed for signs of salmonellosis, and when it became severe, were killed humanely. The livers of the birds were cultured for the inoculated strain on XLD and BGA (Oxoid). Groups of 10 BALB/c mice were inoculated orally directly into the stomach with 107 c.f.u. of the strain to be tested in 50 µl. Mice were observed frequently, and those showing signs of salmonellosis were killed humanely and their livers cultured as above. Statistical analysis was carried out using the chi-square test.

Survival in faeces, water and saline.
Survival in faeces was investigated as follows. Material was collected from the bottom of the cages of chickens that had been infected with either S. Typhimurium F98 or its glgC derivative 3 weeks previously. Fresh samples of faeces, which had been produced within the previous hour, were collected. They were pooled in a glass bottle, and each pool of samples was homogenized crudely with a pestle and mortar. Samples were incubated at room temperature and bacterial counts made at intervals. For survival in water, deionized water was collected into sterile tissue culture bottles, and 50 ml aliquots filtered into 500 ml sterile flasks for use. Bacterial cultures were washed twice in PBS and resuspended in water to a starting count of approximately 106 c.f.u. ml–1. They were incubated statically at 4 and 37 °C. Samples were withdrawn at intervals and the numbers of viable bacteria estimated. For survival in saline, strains were diluted to approximately 1x104 c.f.u. ml–1 in 0·85 % NaCl and incubated without shaking at 37 °C. Bacterial cells were enumerated by plating appropriate dilutions onto Colombia base agar containing 5 % defibrinated horse blood (Oxoid). Statistical analysis was carried out using a two-tailed t test.

Measurement of rpoS expression.
The expression of rpoS in wild-type (WT) and glgC mutant was measured using reporter plasmid pRW50 carrying promoterless lacZY genes inserted behind the rpoS promoter (Lodge et al., 1992). Overnight cultures harbouring the pRW50 : : rpoSlacZ reporter plasmid were inoculated into 10 ml LB supplemented with 5 µg tetracycline ml–1, and incubated with shaking for 2 h. This culture was diluted 1/100 into 100 ml fresh pre-warmed LB supplemented with tetracycline and 0·1 M glucose. WT and glgC mutant strains were analysed for rpoS expression at different times during growth by a {beta}-galactosidase assay (Miller, 1972).


   RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
Glycogen production by different Salmonella serotypes
In total, 256/339 Salmonella strains produced glycogen (Table 2). None of 62 strains of S. Gallinarum or 21 strains of S. Pullorum produced glycogen (Table 2). In contrast, 10/10 strains of S. Enteritidis and 208/208 strains of S. Dublin were positive for glycogen production. These are closely related serotypes, belonging to group D1 (Li et al., 1993). The phenotype of the S. Typhimurium glgC mutant and Glc+ transductants was confirmed after staining with potassium iodide.


View this table:
[in this window]
[in a new window]
 
Table 2. Glycogen production by different Salmonella serotypes and related genera

 
glgC sequence analysis
The glgC gene sequence of S. Gallinarum 9 was 11 bp shorter than that of S. Typhimurium and had a CCC (proline) insertion after position 597 (//;Fig. 1a). Bases 459 to 471 inclusive (13 bp) were replaced by TT, such that the remaining transcribed sequence would have been out of frame, leading to the generation of a number of stop codons. It is likely that the ADP-glucose pyrophosphorylase activity would be non-functional, since the substrate and allosteric effector binding site is thought to be between positions 567 and 594 (Leung & Preiss, 1987b). The complete glgC gene was also sequenced in S. Gallinarum strains 287/91 and 21-92. The sequences were identical, with the same CCC insertion and 11 bp deletion. In addition, recently published incomplete genome sequence information (www.sanger.ac.uk/Projects/Salmonella) indicates shortening of glgB by 52 bp in S. Gallinarum 287/91. The glgC sequence of a single S. Pullorum strain 3 was found to more closely resemble that of S. Typhimurium (Fig. 1b). The published incomplete genome sequence of S. Pullorum (www.salmonella.org/genomics/spu.all) also indicates considerable reductions in the size of glgB and glgP, although this remains to be confirmed.



View larger version (34K):
[in this window]
[in a new window]
 
Fig. 1. Nucleotide sequence of section (424–623) of glgC of S. Typhimurium, indicating differences with respect to the corresponding sequences of (a) S. Gallinarum strains 9, 287/91 and 21-92, and (b) S. Pullorum strain 3. The S. Typhimurium sequence is displayed with nucleotide differences shown above, including the CCC insertion after position 597 and the deletion in the S. Gallinarum sequence between 459–469.

 
Influence of glgC on growth
Yields and exponential-phase growth rates were higher when casamino acids were present (Fig. 2a). The growth rate of S. Typhimurium glgC was only marginally less than that of the parent and did not reach the same final OD in stationary phase. There was little effect of a Glc+ phenotype on the growth of S. Gallinarum; however, Glc+ S. Pullorum achieved a higher OD in log and stationary phase (Fig. 2b). This may be attributed to the increased cell density that occurs with accumulation of intracellular polysaccharide.



View larger version (15K):
[in this window]
[in a new window]
 
Fig. 2. (a) Growth of S. Typhimurium F98 WT (circles) and glgC mutant (squares) in M9 with (closed symbols) and without (open symbols) casamino acids at 37 °C; n=9. (b) Growth of S. Gallinarum 9 WT ({bullet}) and S. Pullorum 3 WT ({blacktriangleup}) and their Glc+ derivatives ({blacksquare} and {blacklozenge}, respectively) in M9 with 0·5 % casamino acids at 37 °C. Error bars show SEM; n=3.

 
Intestinal colonization
The patterns of faecal excretion of S. Typhimurium F98 and its glgC mutant by chickens are shown in Fig. 3. The excretion rates are compared with those of S. Choleraesuis B195, a strain that has been shown not to colonize the avian alimentary tract or be excreted extensively in the faeces (Barrow et al., 1988). The excretion rate of the glgC mutant was marginally less than that of the parent, indicating that it colonized less well, but the differences were not significant. Caecal carriage for the parent and glgC strain was 62 % and 58 %, respectively, at the end of the trial. When naïve chickens were mixed with those infected experimentally (Fig. 3b), the glgC mutant colonized less rapidly over the first 4 weeks, but at the end of the trial, excretion rates were similar.



View larger version (18K):
[in this window]
[in a new window]
 
Fig. 3. Intestinal colonization of chickens by S. Typhimurium F98 NalR and other strains expressed as percentage of chickens in each group excreting the inoculated strain at different times after infection. (a) All chickens inoculated directly; (b) chickens infected by placing them in contact with experimentally infected chickens. Excretion of parent strain ({bullet}); glgC mutant ({blacksquare}) and S. Choleraesuis B195 ({blacktriangleup}) non-colonizing control strain.

 
Virulence of glgC mutants
S. Typhimurium F98 was highly virulent for chickens, with a mortality rate of 18/20 (90 %) in chickens. A reduction of virulence was observed for the glgC mutant, producing mortality in 15/20 (75 %) chickens. This was of marginal statistical significance (P=0·02). When S. Typhimurium F98 and its glgC derivative were cultured in LB broth without glucose, both strains were equally virulent for newly hatched chicks (data not shown). The virulence of the S. Typhimurium glgC mutant in mice was not statistically different from that of the parent (data not shown).

Both S. Gallinarum 9 and its Glc+ transductant produced severe fowl typhoid in all 20 three-week-old chickens inoculated, birds becoming ill at the same rate (data not shown).

Survival in faeces, water and saline
In faeces, the S. Typhimurium glgC mutant survived significantly less well than the parent strain (Fig. 4a). In water at 4 °C, the parent survived better than the glgC strain only after prior culture in LB broth containing 0·5 % glucose. When cultured in LB without glucose, both the glgC mutant and the parent survived equally well during the period of observation (Fig. 4b). At 37 °C, the rate of decline in viability was more rapid, and this was more marked when grown in the spresence of glucose (data not shown). When tested for survival in 0·85 % NaCl, different patterns were observed with S. Typhimurium, S. Gallinarum and S. Pullorum (Fig. 4c, d, e). Up to 7 days, the S. Typhimurium glgC mutant survived as well as the parent, but the numbers fell away more rapidly after this time (Fig. 4c), and by day 12, the glgC mutant survived significantly less well (P<0·05). The Glc+ derivatives of S. Gallinarum and S. Pullorum survived as well as the respective parent strains (Fig. 4d, e).



View larger version (18K):
[in this window]
[in a new window]
 
Fig. 4. Survival of S. Typhimurium F98 WT ({bullet}) and glgC mutant ({blacksquare}) in faeces at 20 °C (a) and in water at 4 °C (b). In (b), the same strains are shown (circles and squares, respectively) cultured with (closed symbols) or without (open symbols) glucose. Survival at 37 °C in saline of S. Typhimurium F98 (c), S. Gallinarum 9 (d) and S. Pullorum 3 (e) WT and the respective glgC mutant (c) or Glc+ transductant (d, e). Mean values from three experiments are shown. {bullet}, WT; {blacksquare}, glgC mutant or Glc+ transductant. Error bars show SEM.

 
rpoS expression in WT and glgC mutant
Since glycogen synthesis is under the control of rpoS (Hengge-Aronis & Fischer, 1992), we wanted to see if mutation in glgC affected rpoS expression in our S. Typhimurium F98 WT and glgC strains. Levels of rpoS expression in the parent strain rose nearly ninefold as the organisms approached stationary phase, as expected. In a glgC background, rpoS promoter activity was reduced by slightly less than 50 %, compared to the parent (Fig. 5).



View larger version (18K):
[in this window]
[in a new window]
 
Fig. 5. Expression of {beta}-galactosidase from the rpoS promoter in plasmid pRW50, during growth in LB supplemented with 0·5 % glucose, in S. Typhimurium F98 WT parent ({bullet} and black bars) and glgC mutant ({square} and white bars). Error bars show SEM; n=3.

 

   DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
We have found that, in common with other members of the Enterobacteriaceae, most Salmonella serotypes produce glycogen. In contrast, none of the strains of the avian pathogens S. Gallinarum and S. Pullorum that were tested produced glycogen under the test conditions. To our knowledge, this is the first report of this phenotype in serovars Gallinarum and Pullorum. The loss of glycogen synthesis ability by these serovars is another example of pseudogene accumulation by host-restricted serovars, and is indicative of functions no longer required due to niche specialization. In addition, host adaptation is often concomitant with extensive gene deletions (Boyd et al., 2003) and complex nutritional requirements, as observed in other host-adapted serovars, such as S. Typhi.

It was initially tempting to attribute the absence of ADP-glucose pyrophosphorylase activity to the major sequence change that was found in the glgC gene of the three strains of S. Gallinarum, which had been isolated from different parts of the world, particularly since the product of the glgC gene is responsible for considerable regulation of glycogen synthesis through allosteric competition by fructose 1,6-bisphosphate (Leung & Preiss, 1987a). However, the absence of this change in S. Pullorum suggested that this was not the sole reason. The ability to transduce these serotypes to a glycogen-positive phenotype suggested that additional mutations to a glycogen-negative phenotype had occurred elsewhere in an ancestor of both these serotypes and presumably within ~40 kb of the adjacent glpD gene. Analysis of the published incomplete sequence showed this to be the case, with different mutations in both glgP and glgB in both serotypes. The absence of the additional accumulation of mutations in the other genes in these operons suggests that the changes have taken place relatively recently, with several additional mutations occurring in the glgC gene of S. Gallinarum.

Glycogen is known to be a major energy reserve in the Enterobacteriaceae, the significance of which has been unclear until relatively recently. Glycogen reserves have been reported to be important for biofilm formation and virulence of S. Enteritidis (Bonafonte et al., 2000). The production of excess glycogen can be induced by mutation in a number of regulatory genes, such as glgX, glgR, glgQ and csrA, the last, at least, of which is known to be pleiotropic (Preiss, 1996; Baker et al., 2002; Dauvillee et al., 2005) and to regulate the expression of some virulence genes (Altier et al., 2000). Glycogen is known to be of importance to sporulating bacteria such as Clostridium and Bacillus (Preiss, 1984), but its known contribution to survival in E. coli has so far been limited to a role in prolonged survival under starvation conditions (Strange, 1968). The literature on the role of glycogen outside the host is apparently conflicting and species specific. The presence of large amounts of glycogen is thought to compromise survival ability in Sarcina lutea (Burleigh & Dawes, 1967). In contrast, accumulation of glycogen acts to promote survival of Streptococcus mitis under starvation conditions (Van Houte & Jansen, 1970). We have found that glycogen production contributes to the survival of S. Typhimurium in faeces and water. However, transductants of serovars Gallinarum and Pullorum expressing glycogen-synthesis ability did not display a fitness advantage. In saline, functional glgC appeared to contribute more to long-term survival. Henrissat et al. (2002) found that a higher proportion of obligately parasitic bacteria lack enzymes for glycogen elaboration and speculated that this is related to lifestyle. On this basis, the avian serovars Gallinarum and Pullorum are more highly adapted to their host than are the other pathogenic serovars. However, the results of our experimental work suggest that the explanation may be more complex.

A running hypothesis was that glycogen reserves increase virulence if the organism has had the opportunity to accumulate them. This occurs with some other storage compounds, such as ferritin (Ftn), so that growth in iron-rich media contributes to survival ability in iron-depleted media, but only when the organisms are pre-grown in iron-rich media (Abdul-Tehrani et al., 1999). However, in our study, there was no indication that WT strains subjected to prior culture in the presence of glucose were more virulent than those pre-cultured in the absence of glucose, although this improved the recovery of organisms from samples. Glycogen production did not contribute to the virulence of serovars Typhimurium or Gallinarum in either an avian or murine model of salmonellosis.

The absence of a major contribution of glycogen to intestinal colonization by S. Typhimurium suggests that if it is indeed produced in the gut, it is also utilized in situ. A recent school of thought suggests that most bacterial growth in the large intestine (caeca/colon) occurs at the interface of the mucosa and the plug/core of chyme (Poulson et al., 1995). Here, bacteria may be able to utilize components of mucin that would contribute to glycogen synthesis. This may enhance survival rates in the core of the caecal contents, where microbial growth is likely to be virtually zero. It may be expected, therefore, that survival of the parent in faeces would be greater than that of a glgC mutant, which is indeed the case.

The relatively minor effect of mutations in glgC on rpoS expression in our experiments was interesting and unexpected, since during starvation, and when glycogen reserves are depleted, RpoS levels might be expected to increase. This shows that the interaction between energy-rich reserves and the small-molecular-mass intracellular metabolites that regulate RpoS expression is complex (Preiss, 1996; Romeo, 1998). Glycogen may provide a steady and non-varying supply of carbon for metabolism and biosynthesis during periods when growth rates may fluctuate considerably and where the replenishment of glycogen and other carbon sources may be intermittent.

In conclusion, under the conditions examined, glycogen has a complex but comparatively minor role in virulence and colonization, but has a more significant role in survival. The fact that S. Typhimurium glgC mutants die off more rapidly in saline, and survive less well in both faeces and water, suggests that glycogen has a role in full survival and, hence, in prolonging the infectivity of broad-host-range Salmonella outside the host.


   ACKNOWLEDGEMENTS
 
The authors would like to acknowledge the Department of the Environment, Food and Rural Affairs (DEFRA), UK, for financial support. A. M. is supported by a scholarship from the British Egg Marketing Board Research and Education Trust, UK.


   REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
 
Abdul-Tehrani, H., Hudson, A. J., Chang, Y.-S., Timms, A. R., Hawkins, C., Williams, J. M., Harrison, P. M., Guest, J. R. & Andrews, C. (1999). Ferritin mutants of Escherichia coli are iron deficient and growth impaired, and fur mutants are iron deficient. J Bacteriol 181, 1415–1428.[Abstract/Free Full Text]

Altier, C., Suyemoto, M. & Lawhon, S. D. (2000). Regulation of Salmonella enterica serovar Typhimurium invasion genes by csrA. Infect Immun 68, 6790–6797.[Abstract/Free Full Text]

Baker, C. S., Morozov, I., Suzuki, K., Romeo, T. & Babitzke, P. (2002). CsrA regulates glycogen biosynthesis by preventing translation of glgC in Escherichia coli. Mol Microbiol 44, 1599–1610.[CrossRef][Medline]

Barrow, P. A., Simpson, J. M., Lovell, M. A. & Binns, M. M. (1987a). Contribution of Salmonella gallinarum large plasmid toward virulence in fowl typhoid. Infect Immun 55, 388–392.[Medline]

Barrow, P. A., Huggins, M. B., Lovell, M. A. & Simpson, J. M. (1987b). Observations on the pathogenesis of experimental Salmonella typhimurium infection in chickens. Res Vet Sci 42, 194–199.[Medline]

Barrow, P. A., Tucker, J. F. & Simpson, J. M. (1987c). Inhibition of colonisation of the chicken alimentary tract with Salmonella typhimurium by Gram-negative facultatively anaerobic bacteria. Epidemiol Infect 98, 311–322.[Medline]

Barrow, P. A., Simpson, J. M. & Lovell, M. A. (1988). Intestinal colonization in the chicken of food-poisoning Salmonella serotypes; microbial characteristics associated with faecal excretion. Avian Pathol 17, 571–588.

Bonafonte, M. A., Solano, C., Sesma, B., Alvarez, M., Montuenga, L., Garcia-Ros, D. & Gamazo, C. (2000). The relationship between glycogen synthesis, biofilm formation and virulence in Salmonella enteritidis. FEMS Microbiol Lett 191, 31–36.[CrossRef][Medline]

Boyd, E. F., Porwollik, S., Blackmer, F. & McClelland, M. (2003). Differences in gene content among Salmonella enterica serovar Typhi isolates. J Clin Microbiol 41, 3823–3828.[Abstract/Free Full Text]

Burleigh, I. G. & Dawes, E. A. (1967). Studies on the endogenous metabolism and senescence of starved Sarcina lutea. J Biochem 102, 236–250.

Chang, D.-E., Smalley, D. J., Tucker, D. L. & 8 other authors (2004). Carbon nutrition of Escherichia coli in the mouse intestine. Proc Natl Acad Sci U S A 101, 7427–7432.[Abstract/Free Full Text]

Dauvillee, D., Kinderf, I. S., Li, Z., Kosar-Hashemi, B., Samuel, M. S., Rampling, L., Ball, S. & Morell, M. K. (2005). Role of the Escherichia coli glgX gene in glycogen metabolism. J Bacteriol 187, 1465–1473.[Abstract/Free Full Text]

Govons, S., Vinopal, R., Ingraham, J. & Preiss, J. (1969). Isolation of mutants of Escherichia coli B altered in their ability to synthesize glycogen. J Bacteriol 97, 970–972.[Medline]

Hengge-Aronis, R. & Fischer, D. (1992). Identification and molecular analysis of glgS, a novel growth-phase-regulated and rpoS-dependent gene involved in glycogen synthesis in Escherichia coli. Mol Microbiol 6, 1877–1886.[Medline]

Henrissat, B., Deleury, E. & Coutinho, P. M. (2002). Glycogen metabolism loss: a common marker of parasitic behaviour in bacteria? Trends Genet 18, 437–440.[CrossRef][Medline]

Jin, X., Ballicora, M. A., Preiss, J. & Geiger, J. H. (2005). Crystal structure of potato tuber ADP-glucose pyrophosphorylase. EMBO J 24, 694–704.[Abstract/Free Full Text]

Leung, P. & Preiss, J. (1987a). Cloning of the ADPglucose pyrophosphorylase (glgC) and glycogen synthase (glgA) structural genes from Salmonella typhimurium LT2. J Bacteriol 169, 4349–4354.[Medline]

Leung, P. & Preiss, J. (1987b). Biosynthesis of bacterial glycogen; primary structure of Salmonella typhimurium ADP glucose synthetase as deduced from the nucleotide sequence of the glgC gene. J Bacteriol 169, 4355–4360.[Medline]

Li, J., Smith, N. H., Nelson, K., Cricton, P. B., Old, D. C., Whittam, T. S. & Selander, R. K. (1993). Evolutionary origin and radiation of the avian-adapted non-motile salmonellae. J Med Microbiol 38, 129–139.[Abstract]

Lodge, J., Fear, J., Busby, S., Gunasekaran, P. & Kamini, N. R. (1992). Broad-range plasmids carrying the Escherichia coli lactose and galactose operons. FEMS Microbiol Lett 74, 271–276.[Medline]

Makinoshima, H., Aizawa, S., Hayashi, H., Miki, T., Nishimura, A. & Ishihama, A. (2003). Growth phase-coupled alterations in cell structure and function of Escherichia coli. J Bacteriol 185, 1338–1345.[Abstract/Free Full Text]

Miller, J. H. (1972). Experiments in Molecular Genetics. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.

Milton, D. L., O'Toole, R., Hörstedt, P. & Wolf-Watz, H. (1996). Flagellin is essential for the virulence of Vibrio anguillarum. J Bacteriol 178, 1310–1319.[Abstract/Free Full Text]

Neidhardt, F. C. (editor) (1996). Metabolism and general physiology. In Escherichia coli and Salmonella – Cellular and Molecular Biology, 2nd edn, pp. 187–1072. Washington, DC: American Society for Microbiology.

Parker, M. T. & Collier, L. H. (1990). In Topley and Wilson's Principles of Bacteriology, Virology and Immunity: Systematic Bacteriology, vol. 2. Edited by M. T. Parker & B. I. Duerden. London: Edward Arnold.

Poulson, L. K., Licht, T. R., Rang, C., Krogfelt, K. A. & Molin, S. (1995). Physiological state of Escherichia coli BJ4 growing in the large intestines of streptomycin-treated mice. J Bacteriol 177, 5840–5845.[Abstract/Free Full Text]

Preiss, J. (1984). Bacterial glycogen synthesis and its regulation. Annu Rev Microbiol 38, 419–458.[CrossRef][Medline]

Preiss, J. (1996). Regulation of glycogen synthesis. In Escherichia coli and Salmonella – Cellular and Molecular Biology, 2nd edn, pp. 1015–1024. Edited by F. C. Neidhardt. Washington, DC: American Society for Microbiology.

Preiss, J. & Romeo, T. (1989). Physiology, biochemistry and genetics of bacterial glycogen synthesis. Adv Microb Physiol 30, 183–238.[Medline]

Romeo, T. (1998). Global regulation by the small RNA-binding protein CsrA and the non-coding RNA molecule CsrB. Mol Microbiol 29, 1321–1330.[CrossRef][Medline]

Romeo, T. & Preiss, J. (1989). Genetic regulation of glycogen biosynthesis in Escherichia coli: in vitro effects of cyclic AMP and guanosine 5'-diphosphate 3'-diphosphate and analysis of in vivo transcripts. J Bacteriol 171, 2773–2782.[Medline]

Romeo, T., Gong, M., Liu, M. Y. & Brun-Zinkernagel, A. M. (1993). Identification and molecular characterisation of csrA, a pleiotropic gene from Escherichia coli that affects glycogen biosynthesis, gluconeogenesis, cell size and surface properties. J Bacteriol 175, 4744–4755.[Abstract]

Sambrook, J. & Russell, D. W. (1989). Molecular Cloning: a Laboratory Manual, 3rd edn. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.

Simon, R., Priefer, U. & Pühler, A. (1983). A broad host range mobilisation system for in vivo genetic engineering: transposon mutagenesis in Gram-negative bacteria. Biotechnology 1, 784–791.[CrossRef]

Smith, H. W. (1955). Observations on experimental fowl typhoid. J Comp Pathol Therapeut 65, 37–54.

Smith, H. W. & Tucker, J. F. (1975). The effect of antibiotic therapy on the faecal excretion of Salmonella typhimurium by experimentally infected chickens. J Hyg Camb 75, 275–292.

Steiner, K. E. & Preiss, J. (1977). Biosynthesis of bacterial glycogen: genetic and allosteric regulation of glycogen biosynthesis in Salmonella typhimurium LT-2. J Bacteriol 129, 246–263.[Medline]

Strange, R. E. (1968). Bacterial ‘glycogen’ and survival. Nature 220, 606–607.[Medline]

Turner, A. K., Lovell, M. A., Hulme, S. D., Zhang-Barber, L. & Barrow, P. A. (1998). Identification of Salmonella typhimurium genes required for colonization of the alimentary tract and for virulence in newly hatched chickens. Infect Immun 66, 2099–2106.[Abstract/Free Full Text]

Van Houte, J. & Jansen, H. M. (1970). Role of glycogen in survival of Streptococcus mitis. J Bacteriol 101, 1083–1085.[Medline]

Zhang-Barber, L., Turner, A. K., Martin, G., Frankel, G., Dougan, G. & Barrow, P. A. (1997). Influence of genes encoding proton-translocating enzymes on suppression of Salmonella typhimurium growth and colonization. J Bacteriol 179, 7186–7190.[Abstract/Free Full Text]

Received 23 June 2005; revised 14 September 2005; accepted 19 September 2005.



This Article
Abstract
Full Text (PDF)
Alert me when this article is cited
Alert me if a correction is posted
Citation Map
Services
Email this article to a friend
Similar articles in this journal
Similar articles in PubMed
Alert me to new issues of the journal
Download to citation manager
Google Scholar
Articles by McMeechan, A.
Articles by Barrow, P. A.
PubMed
PubMed Citation
Articles by McMeechan, A.
Articles by Barrow, P. A.
Agricola
Articles by McMeechan, A.
Articles by Barrow, P. A.


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
INT J SYST EVOL MICROBIOL MICROBIOLOGY J GEN VIROL
J MED MICROBIOL ALL SGM JOURNALS
Copyright © 2005 Society for General Microbiology.