Helicobacter pylori rocF is required for arginase activity and acid protection in vitro but is not essential for colonization of mice or for urease activity

Arginase of the Helicobacter pylori urea cycle hydrolyzes L-arginine to L-o rnithine and urea. H. pylori urease hydrolyzes urea to carbon dioxide and a mmonium, which neutralizes acid. Both enzymes are involved in H. pylori nit rogen metabolism. The roles of arginase in the physiology of H. pylori were investigated in vitro and in vivo, since arginase in H. pylori is metaboli cally upstream of urease and urease is known to be required for colonizatio n of animal models by the bacterium. The H. pylori gene hp1399, which is or thologous to the Bacillus subtilis rocF gene encoding arginase, was cloned, and isogenic allelic exchange mutants of three H. pylori strains were made by using two different constructs: 236-2 and rocF::aphA3. In contrast to w ild-type (WT) strains, all rocF mutants were devoid of arginase activity an d had diminished serine dehydratase activity, an enzyme activity which gene rates ammonium. Compared with WT strain 26695 of H. pylori, the rocF::aphA3 mutant was similar to 1,000-fold more sensitive to acid exposure. The acid sensitivity of the rocF::aphA3 mutant was not reversed by the addition of L-arginine, in contrast to the WT, and yielded a similar to 10,000-fold dif ference in viability. Urease activity was similar in both strains and both survived acid exposure equally well when exogenous urea was added, indicati ng that rocF is not required for urease activity in vitro. Finally, H. pylo ri mouse adapted strain SS1 and the 236-2 rocF isogenic mutant colonized mi ce equally well: 8 of 9 versus 9 of 11 mice, respectively. However, the roc F::aphA3 mutant of strain SS1 had moderately reduced colonization (4 of 10 mice). The geometric mean levels of H. pylori recovered from these mice (in log(10) CFU) were 6.1, 5.5, and 4.1, respectively. Thus, H. pylori rocF is required for arginase activity and is crucial for acid protection in vitro but is not essential for in vivo colonization of mice or for urease activi ty.