CagA delivery by the Helicobacter pylori Cag-Type IV Secretion System confers fitness benefits and costs during stomach infection

Helicobacter pylori strains encoding the cag-pathogenicity island (cag-PAI) and the effector toxin cagA are associated with worse disease outcomes. The cag-PAI encodes the Cag type IV secretion system (Cag-T4SS) which injects CagA and other bacterial products into gastric epithelial cells. Prior work revealed that host adaptive immunity promotes recombination in the cag-PAI gene cagY to attenuate Cag-T4SS activity during chronic infection, suggesting a fitness cost to assembling an active Cag-T4SS. To explore potential selective benefits and costs for the Cag-T4SS and CagA, we employed single strain and competitive infections at both acute and chronic timepoints in wildtype mice and transgenic mice that either attenuate innate immune responses or promote gastric pathology independent of H. pylori infection to examine the relative fitness of mutant H. pylori strains. Our results suggest that an active Cag-T4SS and CagA confer a fitness benefit during initial colonization through Cag-T4SS activity-dependent epithelial cell interactions that activate cancer-related signaling pathways. However, increasing gastric inflammation confers a fitness cost to CagA translocation, promoting Cag-T4SS shutoff. Targeted and whole genome sequencing revealed multiple mechanisms of Cag-T4SS attenuation, with recombination-mediated changes in cagY prevalent at early timepoints and mutations in a variety of Cag-T4SS structural genes accumulating as disease progresses. The need for Cag-T4SS activity and CagA translocation during initial gland colonization likely underlies the mutational pattern observed. Collectively this work reveals new insights into selective constraints on the H. pylori Cag-T4SS as well as resultant genetic adaptation processes that lead to retention of the cag-PAI and virulence.