Global characterization of the Pho regulon in Caulobacter crescentus

Abstract

Bacteria must sense and respond to their environment in order to survive and proliferate. Adapting to phosphate-limited conditions is particularly critical, as phosphate is a central component of many important biomolecules. Most bacteria respond to phosphate limitation through a widely conserved pathway, composed of the phosphate transport Pst system, and downstream signal transduction pathway, PhoR-PhoB, termed the Pho system. In this thesis, I use the model organism Caulobacter crescentus to characterize the response to phosphate limitation. I use ChIP-Seq on the transcriptional regulator PhoB to globally map the Pho regulon in Caulobacter in both phosphate-starved and -replete conditions. I find that the regulatory regions of over 50 genes are bound by PhoB following phosphate limitation, and I identify a consensus PhoB binding motif in Caulobacter. I then examine the function of PhoU, which is a putative negative regulator of the Pho regulon in Caulobacter and many other bacteria. I use morphological and microarray data to demonstrate that PhoU is not a negative regulator of the Pho regulon, and that it instead acts outside the PhoR-PhoB pathway. I find that the function of PhoU is tightly linked to cellular phosphate metabolism. This work offers insight into how Caulobacter responds to nutrient stress, as well as a better understanding of the connectivity and output of the phosphate limitation response pathway.