Hp initiates the stringent response upon nutrient and pH downshift [41]. To determine whether CO2 deprivation induces the stringent response in Hp,

we assessed intracellular nucleotide pools by high-performance liquid chromatography (HPLC) (Figure 8). In the presence of 10% CO2, intracellular ppGpp level was 0.17 nmol per mg bacterial protein, but pppGpp was not detected. Lack of CO2 significantly increased the ppGpp level, suggesting induction of the stringent response. We noted that uracil RG7112 nmr was also significantly higher in cells cultured without CO2. Furthermore, levels of uridine 5′-monophosphate (UMP) and deoxycytidine triphosphate (dCTP), but not cytosine or cytidine-5′-triphosphate (CTP), appeared higher in these cells, although the differences were not significant. Figure 8 Increased

intracellular ppGpp levels in Hp cells in the absence of CO 2 . Hp 26695 was cultured in liquid media for 1 h under an GSK923295 cell line aerobic condition in the absence or presence of 10% CO2, and intracellular nucleotide levels were determined by HPLC analysis. Results are presented as mean ± SD of values obtained from triplicate cultures. Data shown are representative of three independent experiments. Discussion Hp has long been considered a microaerophile that requires O2 for growth but is highly sensitive to atmospheric O2 levels. In the present study, however, we demonstrate C646 clinical trial that atmospheric O2 tension does not kill Hp cells but promotes growth of cells when inoculated at high density, and Hp is unique in that it absolutely requires high CO2 tension for optimal growth Bay 11-7085 and long-term survival. Eliminating the need to remove O2 makes it considerably easier to culture Hp in the laboratory. Bury-Moné et al. reported that Hp strains showed similar growth profiles under aerobic and microaerobic conditions. However, when cells were inoculated in medium containing 0.2% β-cyclodextrin to low density (107 CFU/ml), growth was not detected under 15% O2 and 6% CO2 (generated with CO2 Gen gas packs)

[31]. In contrast, we found that atmospheric O2 tension did not kill Hp cells but did prolong the lag period of cultures inoculated at low cell density (3 × 104 CFU/ml). The conflicting results may have been due to different experimental conditions. We used 10% CO2 to culture Hp, whereas the previous study used 6% CO2. Culture medium pH may increase faster under lower CO2 levels than under 10% CO2, thereby inhibiting bacterial growth, particularly under 20% O2. Further, because the lag period of low-density cultures is prolonged under 20% O2, the culture period in the previous study may have been insufficient to detect growth. Bury-Moné et al. investigated whether growth inhibitory factors played a role in the lack of Hp growth under aerobic conditions.