Identification of a Streptococcus pneumoniae gene locus encoding proteins of an ABC phosphate transporter and a two-component regulatory system

The Escherichia coli Pst system belongs to the family of ABC transporters, It is part of a phosphate (PHO) regulon which is regulated by extracellular phosphate, Under conditions of phosphate limitation, the response regulato r PhoB is phosphorylated by the histidine kinase PhoR and binds to promoter s that share a consensus PHO box, Under conditions of phosphate excess, Pho R, Pst, and PhoU downregulate the PHO regulon. Screening of a library of pn eumococcal mutants with defects in exported proteins revealed a putative tw o-component regulatory system, PnpR-PnpS, and a downstream ABC transporter, similar to the Pst system in E. coli including a gene encoding a PhoU prot ein. Similar to E, coli, mutagenesis of the ATP-binding cassette gene, pstB , resulted in decreased uptake of phosphate, The effects of the loss of the pneumococcal Pst system extended to decreased transformation and lysis, Wi thdrawal of phosphate led to transformation deficiency in the parent strain R6x hut not to penicillin tolerance, suggesting that reduced bacterial dea th was independent of phosphate, None of these phenotypes was observed in t he pneumococcal loss-of-function mutant phoU, By using a lacZ reporter cons truct, it was demonstrated that expression of the two-component regulatory system PnpR-PnpS was not influenced by different concentrations of phosphat e, These results suggest a more complex role of the Pst system in pneumococ cal physiology than in that of E, coli.