Although the Pho regulon system is most widely studied in Escherichia coli it is found in other bacterial species such as Pseudomonas fluorescens and Bacillus subtilis. In Pseudomonas fluorescens, the transcriptional response regulator (PhoB/PhoR) retain the same function they play in E. coli. Bacillus subtilis also shares some similarities when encountering low intracellular phosphate concentrations. Under phosphate-starved conditions B. subtilis binds its transcription regulator, PhoP and the histidine kinase, PhoR to the Pho-regulon gene which induces a production of teichuronic acid. Furthermore, recent studies have suggested the critical role that techoic acid plays in the cell wall of B. subtilis, by acting as a phosphate reservoir and storing the necessary amount of inorganic phosphate in phosphate-starved conditions.