Investigation of the PhoPR two-component signal transduction system in Bacillus subtilis, Staphylococcus aureus and Staphylococcus epidermidis

Abstract

Investigation of the PhoPR two-component signal transduction system in Bacillus subtilis, Staphylococcus aureus and Staphylococcus epidermidis.

Michael Prunty

The PhoPR two-component signal transduction system (TCS) regulates phosphate homeostasis in bacteria (PHO response). It monitors phosphate availability and responds to limiting conditions by directing expression of enzymes to liberate phosphate from macromoleular sources and transport it into the cell. PhoPR has the additional role in Bacillus subtilis of adjusting anionic polymer metabolism to conditions of limited phosphate availability. However, no function has yet been ascribed to PhoPR in Staphylococcus aureus or Staphylococcus epidermidis, nor has it been reported to be involved in staphylococcal pathogenicity. The focus of this study was to further investigate the mechanism of PhoPR activation/deactivation proposed by Botella et al. (2014) in B. subtilis and to establish the physiological role of PhoPR in S. aureus and S. epidermidis. We have established that the PHO responses in B. subtilis subsp subtilis (strain 168) and subsp spizizenii (strain W23) are distinct and we propose that PhoR autokinase activity is initially activated by a surge of the cellular level of either the TagA or TagB enzyme product, both of which are intermediates in wall teichoic acid (WTA) metabolism. We show that while the activation signal for PhoR autokinase activity is the same in both B. subtilis subspecies, the distinct kinetics of their PHO responses emanates from (i) differences in the WTA composition i.e. PhoR autokinase activity is inhibited by poly(glycerol phosphate) but not by poly(ribitol phosphate) WTA biosynthetic intermediates; (ii) differences in genomic organization and (iii) dfference in regulation of expression of the WTA biosynthetic genes. Furthermore, we show that the PhoPR TCS in S. aureus and S. epidermidis plays a similiar role in phosphate homeostasis but is not involved in adjustment of anionic polymer synthesis in these bacteria. A global analysis of PhoPR TCS function in S. aureus shows that when activated, it may also play a role in regulating the expression of a number of important virulence factors.