Helicobacter pylori salvages purines from extracellular host cell DNA utilizing the Outer Membrane-Associated nuclease NucT

Helicobacter pylori is a bacterial pathogen that establishes life-long infections in humans, and its presence in the gastric epitheliumis strongly associated with gastritis, peptic ulcer disease, and gastric cancer. Having evolved in this specific gastric niche forhundreds of thousands of years, this microbe has become dependent on its human host. Bioinformatic analysis reveals that H.pylori has lost several genes involved in the de novo synthesis of purine nucleotides, and without this pathway present, H. pylorimust salvage purines from its environment in order to grow. While the presence and abundance of free purines in various mammaliantissues has been loosely quantified, the concentration of purines present within the gastric mucosa remains unknown.There is evidence, however, that a significant amount of extracellular DNA is present in the human gastric mucosal layer as aresult of epithelial cell turnover, and this DNA has the potential to serve as an adequate purine source for gastric purine auxotrophs.In this study, we characterize the ability of H. pylori to grow utilizing only DNA as a purine source. We show that thisability is independent of the ComB DNA uptake system, and that H. pylori utilization of DNA as a purine source is largely influencedby the presence of an outer membrane-associated nuclease (NucT). A ΔnucT mutant exhibits significantly reduced extracellularnuclease activity and is deficient in growth when DNA is provided as the sole purine source in laboratory growth media.These growth defects are also evident when this nuclease mutant is grown in the presence of AGS cells or in purine-free tissueculture medium that has been conditioned by AGS cells in the absence of fetal bovine serum. Taken together, these results indicatethat the salvage of purines from exogenous host cell DNA plays an important role in allowing H. pylori to meet its purinerequirements for growth.