Phosphate Starvation-Inducible Proteins of Bacillus subtilis : Proteomics and Transcriptional Analysis

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Abstract
The phosphate starvation response in Bacillus subtiliswas analyzed using two-dimensional (2D) polyacrylamide gel electrophoresis of cell extracts and supernatants from phosphate-starved cells. Most of the phosphate starvation-induced proteins are under the control of ςB, the activity of which is increased by energy depletion. In order to define the proteins belonging to the Pho regulon, which is regulated by the two-component regulatory proteins PhoP and PhoR, the 2D protein pattern of the wild type was compared with those of a sigB mutant and aphoR mutant. By matrix-assisted laser desorption ionization–time of flight mass spectrometry, two alkaline phosphatases (APases) (PhoA and PhoB), an APase-alkaline phosphodiesterase (PhoD), a glycerophosphoryl diester phosphodiesterase (GlpQ), and the lipoprotein YdhF were identified as very strongly induced PhoPR-dependent proteins secreted into the extracellular medium. In the cytoplasmic fraction, PstB1, PstB2, and TuaD were identified as already known PhoPR-dependent proteins, in addition to PhoB, PhoD, and the previously described PstS. Transcriptional studies of glpQ and ydhFconfirmed the strong PhoPR dependence. Northern hybridization and primer extension experiments showed that glpQ is transcribed monocistronically from a ςA promoter which is overlapped by four putative TT(A/T)ACA-like PhoP binding sites. Furthermore, ydhF might be cotranscribed withphoB initiating from the phoB promoter. Only a small group of proteins remained phosphate starvation inducible in bothphoR and sigB mutant and did not form a unique regulation group. Among these, YfhM and YjbC were controlled by ςB-dependent and unknown PhoPR-independent mechanisms. Furthermore, YtxH and YvyD seemed to be induced after phosphate starvation in the wild type in a ςB-dependent manner and in the sigB mutant probably via ςH. YxiE was induced by phosphate starvation independently of ςB and PhoPR.

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