Multiple Peptidoglycan Modification Networks Modulate Helicobacter pylori's Cell Shape, Motility, and Colonization Potential

Abstract

Helical cell shape of the gastric pathogen Helicobacter pylori has been suggested to promote virulence through viscosity-dependent enhancement of swimming velocity. However, H. pylori csd1 mutants, which are curved but lack helical twist, show normal velocity in viscous polymer solutions and the reason for their deficiency in stomach colonization has remained unclear. Characterization of new rod shaped mutants identified Csd4, a DL-carboxypeptidase of peptidoglycan (PG) tripeptide monomers and Csd5, a putative scaffolding protein. Morphological and biochemical studies indicated Csd4 tripeptide cleavage and Csd1 crosslinking relaxation modify the PG sacculus through independent networks that coordinately generate helical shape. csd4 mutants show attenuation of stomach colonization, but no change in proinflammatory cytokine induction, despite four-fold higher levels of Nod1-agonist tripeptides in the PG sacculus. Motility analysis of similarly shaped mutants bearing distinct alterations in PG modifications revealed deficits associated with shape, but only in gel-like media and not viscous solutions. As gastric mucus displays viscoelastic gel-like properties, our results suggest enhanced penetration of the mucus barrier underlies the fitness advantage conferred by H. pylori's characteristic shape.

Worldwide Population Structure, Long-Term Demography, and Local Adaptation of Helicobacter pylori

“…We expect that, apart from a generally important role of adaptation to the human gastrointestinal environment, the differing ecophysiological conditions found in the gastric niche of worldwide human hosts, based on diverse diets and different bacterial compositions, could likely generate differential selective pressure on specific bacterial traits leading to locally adaptive events. For instance, an increase in pathogenicity seems to have occurred in H. pylori during the colonization of East Asia and could be partially explained by the presence of different alleles of virulence factors (e.g., CagA, VacA, and OipA; Yamaoka 2010); also, colonization of the stomach niche has been optimized by regulation of motility and by bacterial cell shape (Sycuro et al 2012).To disentangle the signatures of demographic processes from the effects of natural selection on the distribution of allele frequencies, we first investigated the demographic history of our worldwide genome sample. Given that the genetic structure retrieved among the bacterial genomes mirrors the geographic distribution of human populations Breurec et al 2011;Moodley et al 2012), the vast literature on human demographic history provides a solid basis for the study (e.g., Cavalli-Sforza et al 1994), but modeling human-H. pylori coevolution would also require knowledge of transmission dynamics and within-host variation.…”

“…We expect that, apart from a generally important role of adaptation to the human gastrointestinal environment, the differing ecophysiological conditions found in the gastric niche of worldwide human hosts, based on diverse diets and different bacterial compositions, could likely generate differential selective pressure on specific bacterial traits leading to locally adaptive events. For instance, an increase in pathogenicity seems to have occurred in H. pylori during the colonization of East Asia and could be partially explained by the presence of different alleles of virulence factors (e.g., CagA, VacA, and OipA; Yamaoka 2010); also, colonization of the stomach niche has been optimized by regulation of motility and by bacterial cell shape (Sycuro et al 2012).…”

Helical Shape of Helicobacter pylori Requires an Atypical Glutamine as a Zinc Ligand in the Carboxypeptidase Csd4

“…H. pylori is a specialized Gram(Ϫ) human pathogen of the ⑀ class of proteobacteria that colonizes the epithelial surface of the gastric mucous layer and is the causative agent of gastric ulcers and gastric cancer (11). Deletion of H. pylori csd4 led to the loss of helical shape, resulting in slightly curved or straight rods that were impaired in murine stomach colonization assays (8). A similar study in C. jejuni, a closely related human diarrheal pathogen, revealed that deletion of the csd4 homolog, pgp1, led to a similar straight rod phenotype with impaired chick colonization ability, a model representing the natural reservoir of this pathogen (9).…”

Colonize, evade, flourish

“…62 csd4 mutants show a straight rod morphology, suggesting that even seemingly minor trimming of the PG layer can lead to dramatic effects in overall cell morphology. 56 The authors suggest that these changes in PG structure contribute to generation of helical shape in the following ways: localized removal of crosslinks between glycan chains is thought to relax connectivity of the rigid glycan framework at critical points and possibly along multiple axes, creating an offset curvature and twist that generates the helix. Trimming by Csd3 and Csd4 may contribute by limiting cross-linking between shortened muropeptides, or potentially signaling the bacteria to insert new PG fragments as dipeptide indicates aging PG.…”

“…Trimming by Csd3 and Csd4 may contribute by limiting cross-linking between shortened muropeptides, or potentially signaling the bacteria to insert new PG fragments as dipeptide indicates aging PG. 54,56 Importantly, all Csd mutants show defects in colonization of a mouse gastric infection model, but only Csd4 mutants display defects in motility. This phenotype is likely due to the complete lack of curvature in this particular mutant as opposed to the curved Csd1-3 mutants.…”