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Role of the Group B antigen of Streptococcus agalactiae: a peptidoglycan-anchored polysaccharide involved in cell wall biogenesis.

Caliot É, Dramsi S, Chapot-Chartier MP, Courtin P, Kulakauskas S, Péchoux C, Trieu-Cuot P, Mistou MY - PLoS Pathog. (2012)

Bottom Line: Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus.Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis.Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta-hemolytic streptococci.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Unité des Bactéries Pathogènes à Gram positif, Paris, France.

ABSTRACT
Streptococcus agalactiae (Group B streptococcus, GBS) is a leading cause of infections in neonates and an emerging pathogen in adults. The Lancefield Group B carbohydrate (GBC) is a peptidoglycan-anchored antigen that defines this species as a Group B Streptococcus. Despite earlier immunological and biochemical characterizations, the function of this abundant glycopolymer has never been addressed experimentally. Here, we inactivated the gene gbcO encoding a putative UDP-N-acetylglucosamine-1-phosphate:lipid phosphate transferase thought to catalyze the first step of GBC synthesis. Indeed, the gbcO mutant was unable to synthesize the GBC polymer, and displayed an important growth defect in vitro. Electron microscopy study of the GBC-depleted strain of S. agalactiae revealed a series of growth-related abnormalities: random placement of septa, defective cell division and separation processes, and aberrant cell morphology. Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus. Finally, the subcellular localization of the PG hydrolase PcsB, which has a critical role in cell division of streptococci, was altered in the gbcO mutant. Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis. Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta-hemolytic streptococci.

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Structure of GBC and proposed scheme of GBC synthesis.(A) The multiantennary GBC is shown linked to an N-acetyl muramic (NAM) moiety, a component of PG. (B) The figure depicts the first steps of GBC synthesis where GbcO is proposed to catalyze the transfer of UDP-GlcNAc to a lipid phosphate carrier.
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ppat-1002756-g001: Structure of GBC and proposed scheme of GBC synthesis.(A) The multiantennary GBC is shown linked to an N-acetyl muramic (NAM) moiety, a component of PG. (B) The figure depicts the first steps of GBC synthesis where GbcO is proposed to catalyze the transfer of UDP-GlcNAc to a lipid phosphate carrier.

Mentions: Streptococcus agalactiae was first recognized as a veterinary pathogen causing mastitis in cattle and later as a human pathogen responsible for severe neonatal infections [1]–[4]. While it remains a major cause of morbidity and mortality in infants, S. agalactiae is a human commensal that colonizes the rectal and the vaginal mucosa of 15–30% of women [3], [5]. Rebecca Lancefield originally defined two cell wall carbohydrate antigens in S. agalactiae: the group B-specific antigen (GBC) common to all strains and the capsular antigen which currently defines 10 different serotypes (Ia, Ib, II to IX) [6]. The complex multiantennary structure of GBC based on the arrangement of four different oligosaccharides (rhamnose, galactose, N-acetylglucosamine, and glucitol) (Figure 1A) was solved in a series of seminal studies at the end of the 80's [7], [8]. More recently, the capsular polysaccharide and the group B carbohydrate were shown to be covalently bound to the peptidoglycan (PG) at separate sites, i.e. to N-acetylglucosamine and N-acetylmuramic acid respectively [9]. Based on an initial prediction made from genome analysis [10], a comprehensive in silico reconstruction of the biosynthetic pathway of GBC was recently proposed by Sutcliffe and coworkers [10], [11]. Despite the importance of GBC in medical microbiology, the biological role of this surface polysaccharide is unknown and the genetic basis of its biosynthesis was not addressed experimentally.


Role of the Group B antigen of Streptococcus agalactiae: a peptidoglycan-anchored polysaccharide involved in cell wall biogenesis.

Caliot É, Dramsi S, Chapot-Chartier MP, Courtin P, Kulakauskas S, Péchoux C, Trieu-Cuot P, Mistou MY - PLoS Pathog. (2012)

Structure of GBC and proposed scheme of GBC synthesis.(A) The multiantennary GBC is shown linked to an N-acetyl muramic (NAM) moiety, a component of PG. (B) The figure depicts the first steps of GBC synthesis where GbcO is proposed to catalyze the transfer of UDP-GlcNAc to a lipid phosphate carrier.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3375309&req=5

ppat-1002756-g001: Structure of GBC and proposed scheme of GBC synthesis.(A) The multiantennary GBC is shown linked to an N-acetyl muramic (NAM) moiety, a component of PG. (B) The figure depicts the first steps of GBC synthesis where GbcO is proposed to catalyze the transfer of UDP-GlcNAc to a lipid phosphate carrier.
Mentions: Streptococcus agalactiae was first recognized as a veterinary pathogen causing mastitis in cattle and later as a human pathogen responsible for severe neonatal infections [1]–[4]. While it remains a major cause of morbidity and mortality in infants, S. agalactiae is a human commensal that colonizes the rectal and the vaginal mucosa of 15–30% of women [3], [5]. Rebecca Lancefield originally defined two cell wall carbohydrate antigens in S. agalactiae: the group B-specific antigen (GBC) common to all strains and the capsular antigen which currently defines 10 different serotypes (Ia, Ib, II to IX) [6]. The complex multiantennary structure of GBC based on the arrangement of four different oligosaccharides (rhamnose, galactose, N-acetylglucosamine, and glucitol) (Figure 1A) was solved in a series of seminal studies at the end of the 80's [7], [8]. More recently, the capsular polysaccharide and the group B carbohydrate were shown to be covalently bound to the peptidoglycan (PG) at separate sites, i.e. to N-acetylglucosamine and N-acetylmuramic acid respectively [9]. Based on an initial prediction made from genome analysis [10], a comprehensive in silico reconstruction of the biosynthetic pathway of GBC was recently proposed by Sutcliffe and coworkers [10], [11]. Despite the importance of GBC in medical microbiology, the biological role of this surface polysaccharide is unknown and the genetic basis of its biosynthesis was not addressed experimentally.

Bottom Line: Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus.Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis.Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta-hemolytic streptococci.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Unité des Bactéries Pathogènes à Gram positif, Paris, France.

ABSTRACT
Streptococcus agalactiae (Group B streptococcus, GBS) is a leading cause of infections in neonates and an emerging pathogen in adults. The Lancefield Group B carbohydrate (GBC) is a peptidoglycan-anchored antigen that defines this species as a Group B Streptococcus. Despite earlier immunological and biochemical characterizations, the function of this abundant glycopolymer has never been addressed experimentally. Here, we inactivated the gene gbcO encoding a putative UDP-N-acetylglucosamine-1-phosphate:lipid phosphate transferase thought to catalyze the first step of GBC synthesis. Indeed, the gbcO mutant was unable to synthesize the GBC polymer, and displayed an important growth defect in vitro. Electron microscopy study of the GBC-depleted strain of S. agalactiae revealed a series of growth-related abnormalities: random placement of septa, defective cell division and separation processes, and aberrant cell morphology. Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus. Finally, the subcellular localization of the PG hydrolase PcsB, which has a critical role in cell division of streptococci, was altered in the gbcO mutant. Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis. Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta-hemolytic streptococci.

Show MeSH
Related in: MedlinePlus