Regulation of the pstSCAB operon in Corynebacterium glutamicum by the regulator of acetate metabolism RamB

The pstSCAB operon of Corynebacterium glutamicum, which encodes an ABC transport system for uptake of phosphate (Pi), is induced during the P i starvation response. The two-component regulatory system PhoRS is involved in this response, but partial Pi starvation induction of pstSCAB in a ∆phoRS mutant indicated the involvement of additional regulator(s). Regulation of pstSCAB also involves the global transcriptional regulator GlxR. DNA affinity chromatography identified the regulator of acetate metabolism RamB as a protein binding to pstS promoter DNA in vitro. Gel mobility shift assays and mutational analysis of the pstS promoter region revealed that RamB binds to two sites localized at positions -74 to -88 and -9 to +2 with respect to the transcriptional start site of pstSCAB. Reporter gene studies supported the in vivo relevance of both binding sites for activation of pstSCAB by RamB. DNA microarray analysis revealed that expression of many Pi starvation inducible genes reached higher levels during the Pi starvation response on minimal medium with glucose as sole carbon source than in Pi starved acetate-grown C. glutamicum cells. In C. glutamicum, RamB is involved in expression control of pstSCAB operon. Thus, transcriptional regulation of pstSCAB is complex involving activation by the phosphate-responsive two-component regulatory system PhoSR and the regulators of carbon metabolism GlxR and RamB. Gene expression of C. glutamicum ATCC13032 after 90 min of phosphate starvation was compared in CGXII medium with different carbon sourse (4% glucose or 2% acetate) at the exponential growth phase. Biological duplicates were analyzed with dye-swaps.