Mechanisms and implications of two-component signal transduction in Campylobacter jejuni

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The ability of bacteria to sense and respond to different conditions is essential to their survival. A conserved means to enact this is the two-component signal transduction system (TCS). In typical two-component systems, a sensor protein on the bacterial surface senses an external signal and activates a regulator protein in the cytoplasm. The regulator then binds DNA to alter gene expression, which in turn alters bacterial behavior in response to the signal. The organism we study, Campylobacter jejuni, is a prevalent enteric pathogen that lives optimally inside commensal animal hosts such as chickens. However, it can also survive (and often thrive) in unfavorable environments such as water and food processing plants, in the dirt, and on poultry surfaces in the grocery store, as well as within susceptible human hosts. Paradoxically, the percentage of the C. jejuni genome devoted to regulatory genes such as TCSs is much smaller than that of other enteric bacteria like E. coli and more similar to the human stomach-restricted Helicobacter pylori. These observations led us to hypothesize that critical TCSs in C. jejuni will control multiple aspects of the C. jejuni lifestyle. Indeed, we have found that the TCSs that form the basis of this research program are required for survival in chickens and also modulate key aspects of bacterial physiology. The goal of this research program is to identify which genes these systems influence both directly and indirectly, explore other bacterial factors that may interact with these systems, and reveal signals to which the systems respond. This will provide insight into important mechanisms governing C. jejuni behavior and provide models for other organisms which may likewise need to traverse diverse niches using limited regulatory machinery.