The physiology and metabolism of Campylobacter jejuni and Helicobacter pylori

Summary, 16S 2. Introduction, 16S 3. Characteristics of Campylobacter jejuni and Helicobacter pylori, 17S 3.1 Associations with disease, 17S 3.2 Growth requirements and the spiral to coccoid cell transition, 17S 4. Solute transport systems, 18S 4.1 Overview, 18S 4.2 Iron acquisition, 18S 5. Central metabolic pathways, 18S 5.1 Experimental approaches, 18S 5.2 Carbon catabolism and anaplerotic reactions, 19S 5.3 2‐Oxoacid metabolism and the citric acid cycle, 19S 6. Electron transport chains, 20S 6.1 Campylobacter jejuni, 20S 6.2 Helicobacter pylori, 20S 7. Microaerobic growth and carbon dioxide requirement, 20S 7.1 Microaerophily and oxidative stress, 20S 7.2 Carbon dioxide requirement, 21S 8. Conclusions, 21S 9. Acknowledgements, 22S 10. References, 22S Although closely related phylogenetically and sharing many phenotypic similarities, Campylobacter jejuni and Helicobacter pylori are distinct in some major aspects of their physiology and metabolism. In this paper, comparative aspects of the physiology of these pathogens is discussed in the light of recent biochemical and genome sequence data. Campylobacter jejuni is emerging as a more versatile and metabolically active pathogen, with a complete citric acid cycle, and a complex and highly branched respiratory chain which allows both aerobic and anaerobic respiration with a variety of alternative electron acceptors. These properties enable it to survive in a number of environments in addition to the mammalian or avian gut. In vivo, anaerobic growth of C. jejuni could be an important factor allowing intestinal colonization. Helicobacter pylori is a more specialized pathogen, largely restricted to the human stomach, with a unique combination of virulence factors, an incomplete citric acid cycle, a simpler respiratory chain with only a single terminal oxidase and fewer regulatory systems. Both bacteria are microaerophiles and, while there is likely to be no single explanation for their oxygen sensitivity, there is evidence that the possession of oxygen‐sensitive enzymes and an increased sensitivity to oxidative stress play an important role.