The Phosphate Starvation Stimulon ofCorynebacterium glutamicumDetermined by DNA Microarray Analyses

Abstract

The phosphate (P i ) starvation stimulon of Corynebacterium glutamicum was characterized by global gene expression analysis by using DNA microarrays. Hierarchical cluster analysis of the genes showing altered expression 10 to 180 min after a shift from P i -sufficient to P i -limiting conditions led to identification of five groups comprising 92 genes. Four of these groups included genes which are not directly involved in P metabolism and changed expression presumably due to the reduced growth rate observed after the shift or to the exchange of medium. One group, however, comprised 25 genes, most of which are obviously related to phosphorus (P) uptake and metabolism and exhibited 4-to >30-fold-greater expression after the shift to P i limitation. Among these genes, the RNA levels of the pstSCAB (ABC-type P i uptake system), glpQ (glycerophosphoryldiester phosphodiesterase), ugpAEBC (ABC-type sn-glycerol 3-phosphate uptake system), phoH (unknown function), nucH (extracellular nuclease), and Cgl0328 (5-nucleotidase or related esterase) genes were increased, and pstSCAB exhibited a faster response than the other genes. Transcriptional fusion analyses revealed that elevated expression of pstSCAB and ugpAEBC was primarily due to transcriptional regulation. Several genes also involved in P uptake and metabolism were not affected by P i starvation; these included the genes encoding a PitA-like P i uptake system and a putative Na ؉ -dependent P i transporter and the genes involved in the metabolism of pyrophosphate and polyphosphate. In summary, a global, time-resolved picture of the response of C. glutamicum to P i starvation was obtained.Phosphorus (P) is an indispensable component of all cells in living organisms. In bacteria, P typically is assimilated as inorganic orthophosphate (P i ), which is transported into the cell by specific uptake systems. Alternatively, organophosphates and phosphonates may serve as sole P sources; either these compounds are imported by specific uptake systems and degraded intracellularly or P i that is liberated by extracellular degradation of the compounds is taken up into the cell. For several bacteria, particularly Escherichia coli and Bacillus subtilis, P metabolism and the regulatory mechanisms that permit adaptation to varying P availability have been well studied (22,47).E. coli possesses three P i uptake systems (19). PitA is expressed constitutively and transports phosphate in a proton motive force-dependent manner (47). When the extracellular P i concentration falls below about 4 M, P i is taken up primarily by the Pst system at the expense of ATP. The Pst system is an ABC transport system encoded by the pstSCAB genes of the pstSCAB-phoU operon, which is induced under P i starvation conditions (47). When formed, the PitB transporter encoded by a cryptic homolog of pitA is able to transport P i in a manner similar to the manner used by PitA (19). The genes constituting the P i starvation stimulon were identified in screening analyses based on transcriptional lacZ fusions (32) an...

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