Characteristics of the aerobic respiratory chains of the microaerophiles Campylobacter jejuni and Helicobacter pylori

The respiratory chain enzymes of microaerophilic bacteria should play a maj or role in their adaptation to growth at low oxygen tensions. The genes enc oding the putative NADH:quinone reductases (NDH-1), the ubiquinol:cytochrom e c oxidoreductases (bc(1) complex) and the terminal oxidases of the microa erophiles Campylobacter jejuni and Helicobacter pylori were analysed to ide ntify structural elements that may be required for their unique energy meta bolism. The gene clusters encoding NDH-1 in both C. jejuni and H. pylori la cked nuoE and nuoF, and in their place were genes encoding two unknown prot eins. The NuoG subunit in these microaerophilic bacteria appeared to have a n additional Fe-S cluster that is not present in NDH-1 from other organisms , but C. jejuni and H. pylori differed from each other in a cysteine-rich s eg ment in this subunit, which is present in some but not all NDH-1. Both o rganisms lacked genes orthologous to those encoding NDH-2. The subunits of the bc(1) complex of both bacteria were similar, and the Rieske Fe-S and cy tochrome b subunits had significant similarity to those of Paracoccus denit rificans and Rhodobacter capsulatus, well-studied bacterial bc(1) complexes . The composition of the terminal oxidases of C. jejuni and H. pylori was d ifferent; both bacteria had cytochrome cbb(3) oxidases, but C. jejuni also contained a bd-type quinol oxidase. The primary structures of the major sub units of the cbb(3)-type (terminal) oxidase of C. jejuni and H. pylori indi cated that they form a separate group within the cbb(3) protein family. The implications of the results for the function of the enzymes and their adap tation to microaerophilic growth are discussed.