Campylobacter jejuni is an important pathogen that causes human bacterial gastroenteritis worldwide and can colonise the intestinal mucosa of all food-producing animals. Under such conditions C. jejuni is able to tolerate a variety of stresses, which they must in order to permit their transmission to a suitable environment for growth. C. jejuni is an obligate microaerophile, with the ability to survive in oxygen conditions and the natural environment indicating a potential to carry out aerobic respiration. This, in principle, allows growth in the absence and presence of oxygen. Despite its importance, effective control of Campylobacter spp. in the food chain and the design of disease prevention strategies are restricted by a poor understanding of the genetics, physiology and virulence of this organism. Therefore, to gain a greater understanding of its survival in different environments, it is important to understand how the respiratory pathway functions in C. jejuni in order to gain a greater understanding of its physiology. C. jejuni encodes a large respiratory enzyme complex, named NDH-I or complex I, which is composed of 14 different genes designated as the nuo operon. These genes are clustered in a conserved order in bacteria like Escherichia coli and Paracoccus denitrificans, however in C. jejuni the subunits nuoE and nuoF have been replaced by two subunits of unknown function, designated NuoX and NuoY (encoded by cj1575c and cj1574c genes respectively).