The cytoplasmic phosphate level has a central regulatory role in the phosphate starvation response of Caulobacter crescentus

In bacteria, the availability of environmental inorganic phosphate is typically sensed by the conserved PhoRB two-component signaling pathway, which uses the flux through the Pst phosphate trans­porter as a readout of the extracellular phosphate level to control a variety of phosphate-responsive genes. While the sensing of environmental phosphate is well-established, the regulatory effects of cyto­plas­mic phos­phate are still unclear. Here, we disentangle the physiological and transcriptional responses of Caulo­bacter crescentus to chan­­ges in the environmental and cyto­plasmic phos­phate levels. To this end, we are uncoupling phosphate uptake from the activity of the Pst system by producing an additional, hetero­logous phosphate transporter. This approach reveals a bi-pronged response of C.crescentus to phos­phate limitation, in which the PhoRB signaling mostly facilitates the utilization of alternative phosphate sour­ces, whereas the cyto­plasmic phosphate level controls the morphological and physiological adap­tation of cells to growth in conditions of global phosphate limitation. These findings open the door to a more comprehensive under­standing of phosphate signaling in bacteria. Duplicate mRNA profiles of C. crescentus WT and mutant (ΔphoB and ΔpstS) cells expressing or not the heterologous PitA transporter from Escherichia coli, were generated by next-generation sequencing with an Illumina NextSeq 500. We next procceeded to comparative transcript analysis of the phosphate strarved mutants (ΔphoB and ΔpstS) against strains with restored cytoplamsic phosphate levels either due to the presence of the PitA transporter (ΔphoB Pxyl::Pxyl-PitA and ΔpstS Pxyl::Pxyl-PitA) or due to the presence of the native Pst transport system (WT and WT Pxyl::Pxyl-PitA)