Role of the Group B Antigen of Streptococcus agalactiae: A Peptidoglycan-Anchored Polysaccharide Involved in Cell Wall Biogenesis

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.

SpyAD, a Moonlighting Protein of Group A Streptococcus Contributing to Bacterial Division and Host Cell Adhesion

“…As previously reported (28)(29)(30), the depletion of proteins involved in the cell division/separation process in both Gram-positive and Gram-negative bacteria produces a phenotype very similar to that observed with the spyAD knockout strain.…”

The Capsular Polysaccharide of Staphylococcus aureus Is Attached to Peptidoglycan by the LytR-CpsA-Psr (LCP) Family of Enzymes

“…This step is poorly characterized and the molecular principles for capsule attachment in Gram-positive bacteria have rarely been addressed. For example, NMR analysis of mutanolysin cleaved sacculi revealed that CPS type III of GBS is linked via a glycosidic linker to N-acetylglucosamine residues of peptidoglycan (6), whereas the Lancefield group B carbohydrate of GBS appears to be linked to N-acetylmuramic residues of peptidoglycan with an intervening linkage unit (6,58). In Bacillus anthracis, the capsule is composed of a poly-D-␥-glutamate polymer, and is also attached to peptidoglycan.…”

“…7). Considering the involvement of LCP proteins in transferring polymers for which synthesis is initiated by TagO (31,37,50,51,58,59,66,67), we examined whether capsule assembly requires tagO in S. aureus. Furthermore, recent work has shown that heterologous expression of Pseudomonas aeruginosa O11 lipopolysaccharide synthesis genes, which include wbpL, a UDP-FucNAc-1-phosphate transferase, together with CP5 genes capHIJK was sufficient to synthesize lipid-linked CP5 polymer repeats in E. coli (68).…”

GacA is essential for Group A Streptococcus and defines a new class of monomeric dTDP‐4‐dehydrorhamnose reductases (RmlD)

“…Teichoic or teichuronic acids are typical and well‐studied SCWP in Gram‐positive bacteria and play an important role in normal cell function and infection (Weidenmaier and Peschel, 2008). Many β‐hemolytic streptococcal species appear to lack expression of typical teichoic or teichuronic acid structures (Sutcliffe et al ., 2008; Caliot et al ., 2012) and instead express a rhamnose‐rich polymer, which comprises approximately half of the cell wall mass (McCarty, 1952). Historically, expression of these evolutionary conserved glycans underlies classification of β‐hemolytic streptococci in Lancefield groups (A, B, C, G …) (Lancefield, 1933), a feature that is still applied in contemporary rapid test kits to diagnose streptococcal infections.…”