In addition, Hp uses anaerobic respiration utilizing H2 as an electron donor [16]. Since its discovery in 1984, Hp has been considered

a microaerophilic bacterium highly susceptible to environmental O2 tension [17]. Hp is a spiral-shaped bacillus that, when exposed to a high O2 concentration, converts to a full coccoid form that is viable but nonculturable [18, 19]. Hp is generally cultured under microaerobic conditions using a GasPak or CO2 chamber to achieve adequate growth, and its cultivation can be difficult and cumbersome [20]. Therefore, significant www.selleckchem.com/products/bmn-673.html efforts have been made to increase the efficiency of Hp cultivation [21–23]. There are many hypotheses for the microaerophilic requirements of bacteria: high sensitivity to toxic forms of oxygen present in the culture medium, excessive metabolic generation of toxic forms of oxygen, low respiratory rates, iron deficiency, lack of protective enzymes, unusually oxygen-sensitive cell constituents, and reliance on oxygen-labile

substrates (see reference [24] for review). The antioxidant defense system of Hp has been studied extensively VS-4718 because of its unique microaerophilic nature and clinical importance. Hp has been found to express oxidative stress resistance enzymes including superoxide dismutase (SodB), catalase (KatA), as well as peroxiredoxins, alkyl hydroxide reductases, bacterioferritin co-migratory protein and thiol peroxidase (see reference [25] for review). In addition, Hp expresses neutrophil-activating protein (NapA), which protects cells from oxidative stress damage, DNA repair proteins (Nth, MutS, RuvC), an oxidized protein repair system (Msr), and the thioredoxin system (thioredoxin and thioredoxin reductase) [25]. Despite these diverse antioxidant systems, Hp remains vulnerable to the toxicity of environmental levels of oxygen. Several lines of evidence have suggested that Hp may not be microaerophilic. Hp strains exhibit

a range of susceptibility to high O2 tension, Chlormezanone and two strains adapted to aerobic growth have been isolated [26]. In addition, researchers, including our group, routinely culture Hp strains in regular incubators supplied with 5% to 10% CO2 [27–30]. Bury-Moné et al. recently reported that at a high cell density and in the presence of 5% CO2, Hp showed similar growth profiles in liquid cultures under microaerobic and aerobic conditions, suggesting that Hp may not be microaerophilic [31]. Despite the clinical importance and extensive studies of Hp, many basic aspects of its microaerophilicity remain unclear. To extend our knowledge of its pathogenesis in host environments, we must first elucidate its response to O2 to characterize its physiology and energy metabolism.