A peptide of a type I toxin−antitoxin system induces Helicobacter pylori morphological transformation from spiral shape to coccoids

Abstract

Toxin−antitoxin systems are found in many bacterial chromosomes and plasmids with roles ranging from plasmid stabilization to biofilm formation and persistence. In these systems, the expression/activity of the toxin is counteracted by an antitoxin, which, in type I systems, is an antisense RNA. While the regulatory mechanisms of these systems are mostly well defined, the toxins’ biological activity and expression conditions are less understood. Here, these questions were investigated for a type I toxin−antitoxin system (AapA1−IsoA1) expressed from the chromosome of the human pathogen Helicobacter pylori. We show that expression of the AapA1 toxin in H. pylori causes growth arrest associated with rapid morphological transformation from spiral-shaped bacteria to round coccoid cells. Coccoids are observed in patients and during in vitro growth as a response to different stress conditions. The AapA1 toxin, first molecular effector of coccoids to be identified, targets H. pylori inner membrane without disrupting it, as visualized by cryoelectron microscopy. The peptidoglycan composition of coccoids is modified with respect to spiral bacteria. No major changes in membrane potential or adenosine 5′-triphosphate (ATP) concentration result from AapA1 expression, suggesting coccoid viability. Single-cell live microscopy tracking the shape conversion suggests a possible association of this process with cell elongation/division interference. Oxidative stress induces coccoid formation and is associated with repression of the antitoxin promoter and enhanced processing of its transcript, leading to an imbalance in favor of AapA1 toxin expression. Our data support the hypothesis of viable coccoids with characteristics of dormant bacteria that might be important in H. pylori infections refractory to treatment.

Myricetin as an Antivirulence Compound Interfering with a Morphological Transformation into Coccoid Forms and Potentiating Activity of Antibiotics against Helicobacter pylori

“…In the present study, we observed that MYR seems to have a stronger influence on the second stage of H. pylori murein modification (trimming of muropeptide monomers), with an approximately 4-fold reduction in the expression of these genes ( Figure 8 ). This is consistent with the observations showing the importance of dipeptides accumulation in coccoid H. pylori forms [ 35 , 36 , 37 ], and the participation of csd4 and amiA as determinants of this morphological transformation in both H. pylori [ 36 , 56 ] and Campylobacter jejuni [ 57 ]. Taking into account our results, we suspect that MYR may be responsible for the disturbance of the csd3 and csd6 activity (contributing to the decrease of substrates for the csd4 functioning), as well as the inhibition of amiA , a gene coordinating the work of the aforementioned determinants.…”

“…In this case, we selected genetical determinants involved in the peptidoglycan modeling, i.e., cleaving of cross-linking bridges of muropeptide dimers ( csd1, csd2 , and csd3 ) and shortening of muropeptide monomers ( csd3, csd6, csd4 , and amiA ) [ 25 ]. In particular, the activity of genes associated with the second peptidoglycan rearrangement pathway seemed important to us as it has been suggested that the trimming of penta-, tetra-, and tripeptides to dipeptides is a molecular marker associated with the formation of spherical H. pylori forms [ 35 , 36 , 37 ].…”

Toxin-Antitoxin Systems - A New Player in Morphological Transformation of Antibiotic-Exposed Helicobacter pylori?

“…(2017) , who first identified the existence of the type I TA system in H. pylori (called AapA1-IsoA1), and noted that the expression of the toxin significantly decreases the amount of culturable H. pylori cells. At this point it is worth mentioning that Mortaji et al. (2020) deepened the knowledge related to the above phenomenon.…”

“…The recently published original article by Mortaji et al. (2020) characterized for the first time the function of a type I toxin-antitoxin (TA) system in the gastric pathogen Helicobacter pylori .…”

“…(2020) deepened the knowledge related to the above phenomenon. They proved in their next original article that this decline was caused by a reduction in the culturability (observed as the optical density of the culture) but not the viability of H. pylori (preserved cell membrane integrity and a stable ATP level), and was accompanied by the transition of morphology from spiral to coccoidal ( Mortaji et al., 2020 ). This observation is very valuable from the scientific point of view and confirms the postulates presented by our research group, pointing to difficulties in the correct interpretation of the H. pylori viability (understood as the sum of various cell parameters suggesting its physiological activity) and frequent mistakes made by scientists taking the culturability (detected by culture optical density or CFU/mL) as the only determinant of the viability of this pathogen ( Krzyżek and Grande, 2020 ).…”