The enigma of oxygen intolerance in Campylobacter jejuni: an integrative transcriptomic proteomic and physiological approach

Some bacteria get into the food that we eat and cause food-poisoning. Some of these bacteria are quite common but are usually killed during cooking. When chicken meat is not cooked properly, one of these types of bacteria, called Campylobacter jejuni, is a particular problem. If we can understand what allows C.jejuni to grow in chickens and reduce the level of contamination of chicken carcasses, this will help reduce the scale of the risk to human health. In the chicken gut, the oxygen concentrations are very low and C. jejuni has to adapt it's metabolism to this environment. This project is aimed at understanding how this happens and what genes and proteins are important in regulating this process. We will be looking at how the bacterium copes with low oxygen concentrations on the one hand, but also how it resists the potentially damaging effects of oxidative stress when it comes into contact with high oxygen levels. We will do this by using special continuous growth techniques in an apparatus called a fermenter. The results should help us to identify specific genes or proteins that are important in growth at high or low oxygen levels and these might be targets for intervention that might in the future allow the control of the growth of the bacteria in the chicken gut.

Campylobacter jejuni is a microaerophile which requires oxygen for growth, but is unable to grow at normal atmospheric oxygen tensions. The molecular bases for oxygen inhibition of growth on the one hand, and an oxygen requirement on the other, are very poorly understood in this pathogen. One problem that confounds comparative studies at a range of oxygen tensions in batch cultures is changes in growth rate and other cellular parameters that will have secondary effects on gene expression. In this project we propose to use defined chemostat cultures of Campylobacter jejuni, which will be carbon-limited at a constant growth rate, in which the oxygen tension can be varied to establish a series of steady-states. These will be sampled to determine any differences in gene and protein expression, using a combined transcriptomic and proteomic approach. Because cells are derived from cultures at the same growth rate, we will be able to ensure that changes that we observe are due to the influence of oxygen. Comparative changes in the activities of the respiratory chains and key metabolic enzymes will be compared with these results, in order to test hypotheses concerning the oxygen sensitivity of this pathogen. We are thus particularly interested in genes and proteins, which show significant up- or down-regulation/activity at oxygen tensions above that for optimum growth (yield) and these will be subjected to mutagenesis, phenotypic and proteomic analysis. The aim is to obtain an accurate picture of the molecular responses of this important pathogen to changes in oxygen. (Joint with BB/E014429/1)