Analysis of the role of the TAT protein translocation system in Campylobacter jejuni

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 certain proteins which are needed in this adaptation and which often function outside the cell, get to their final location using a special type of export system. We will try to find out what happens when the cell is prevented from exporting these proteins, and what the functions of some of them are. The results should help us to understand better the role that these types of exported proteins play in the overall biology of campylobacter and may even identify specific targets for intervention that might in the future allow the control of the growth of the bacteria in the avian gut.

Many of the primary dehydrogenases and terminal reductases in the electron transport chains of Campylobacter jejuni possess a 'twin-arginine' translocase (TAT) recognition motif, indicating that protein export by the TAT system may be crucial in the respiratory physiology of C. jejuni. However, in other bacteria it is now clear that the functions of the TAT system extend far beyond the assembly of electron transport chains, to include cell wall biosynthesis, adaptation to different growth conditions and virulence. We have identified a significant number of additional potential TAT substrates in C. jejuni, and now wish to understand the wider importance of the TAT system in this pathogen. In preliminary work we have constructed a tatC mutant and have characterised several novel TAT substrates. In this project we will (i) determine the consequences of the loss of the TAT system, by a detailed analysis of the phenotype of tatA and tatC mutants, (ii) Undertake a proteomic analysis of wild-type and tat mutant strains, to identify TAT substrate proteins and compare with predictions from the genome sequence and to determine the global effects of protein mislocalisation in tat mutants (iii) Investigate the physiological functions of a small selection of putative TAT substrates by a combination of mutageneis and biochemical characterisation of heterologously expressed protein.