Background: The β and β′ subunits of RNA polymerase are fused in all Helicobacters, but separate in most other taxa. Prior studies had shown that this fusion is not essential for viability in culture or in vivo, but had not tested it for potentially important quantitative effects on phenotype. Methods: The effect of separating rpoB and rpoC sequences on Helicobacter pylori growth was tested in culture and during mouse infection. Results: Derivatives of strains X47 and SS1 carrying this "rpoBCsplit" allele colonized mice less vigorously than their wild-type parents in competition tests. With X47 rpoBCsplit, this reduced vigor was evident in wild-type mice, whereas with SS1 rpoBCsplit it was seen only in cytokine IL-10- and IL-12β-deficient mice. In culture, the rpoBCsplit allele sensitized each of four strains tested (X47, SS1, 88-3887, and AM1) to urea, a metabolite that is secreted into the gastric mucosa; urea sensitization was more severe in X47 than in SS1 genetic backgrounds. The rpoBCsplit allele also caused poorer growth on Ham's F12 agar, a nutritionally limiting medium, but had little effect on sensitivity to mild acidity. Conclusions: H. pylori's normal RNA polymerase β-β′ subunit fusion contributes quantitatively to fitness. We propose that urea, although important to H. pylori in vivo, also be considered inhibitory; and that H. pylori's natural β-β′ subunit fusion helps it cope with urea exposure.
- Mouse infection