Terminal Oxidases Are Essential To Bypass the Requirement for ResD for Full Pho Induction in Bacillus subtilis

Abstract

The Bacillus subtilis Pho signal transduction network, which regulates the cellular response to phosphate starvation, integrates the activity of three signal transduction systems to regulate the level of the Pho response. This signal transduction network includes a positive feedback loop between the PhoP/PhoR and ResD/ResE two-component systems. Within this network, ResD is responsible for 80% of the Pho response. To date, the role of ResD in the generation of the Pho response has not been understood. Expression of two terminal oxidases requires ResD function, and expression of at least one terminal oxidase is needed for the wild-type Pho response. Previously, our investigators have shown that strains bearing mutations in resD are impaired for growth and acquire secondary mutations which compensate for the loss of the a-type terminal oxidases by allowing production of cytochrome bd. We report here that the expression of cytochrome bd in a ⌬resDE background is sufficient to compensate for the loss of ResD for full Pho induction. A ctaA mutant strain, deficient in the production of heme A, has the same Pho induction phenotype as a ⌬resDE strain. This demonstrates that the production of a-type terminal oxidases is the basis for the role of ResD in Pho induction. Terminal oxidases affect the redox state of the quinone pool. Reduced quinones inhibit PhoR autophosphorylation in vitro, consistent with a requirement for terminal oxidases for full Pho induction in vivo.The Bacillus subtilis phosphate starvation response (Pho response) is under the control of a complex regulatory network that allows the cell to respond to the level of inorganic phosphate (P i ) in the environment. This system is critical to survival because phosphate is the limiting nutrient in soil (33), the natural environment for B. subtilis.Central to the B. subtilis Pho response is the PhoP/PhoR two-component signal transduction system. The phoPR operon (23, 43) is subject to activation by PhoP under phosphate starvation conditions (34). PhoP/PhoR directly regulates the expression of genes involved in the cellular response to phosphate starvation. The histidine kinase, PhoR, is autophosphorylated in response to an environmental signal and then phosphorylates its cognate response regulator, PhoP. PhoPϳP activates the transcription of the alkaline phosphatases (19), phoA (formerly phoAIV) (20), and phoB (formerly phoAIII) (7); phosphodiesterases, phoD (11), and glpQ (1); a high-affinity phosphate transport system, pstS (37); teichuronic acid synthetic genes (teichuronic acid is a cell wall polymer lacking phosphate), tuaABCDEFGH (27, 46); and a gene encoding a 60-residue peptide of unknown function, ykoL (38). PhoPϳP has been shown to repress the expression of the tagAB and tagDEF genes responsible for the production of teichoic acid (a cell wall polymer containing phosphate) (26). The collective action of these products allows the cell to scavenge extracellular phosphate and to release additional P i from the cell wall.The regulation of the Pho respon...

Direct Regulation ofBacillus subtilis phoPRTranscription by Transition State Regulator ScoC

“…Reduced quinones were shown to inhibit autophosphorylation of the PhoR in vitro, suggesting that it was the ResD role in terminal oxidase production that positively modulates the PhoR signal (35) upstream of PhoPR. Consistent with this idea, resD mutants containing a spontaneous mutation in rex (formerly ydiH), a repressor of cydABCD encoding bd oxidase (34), allowed expression of cydABCD during Pho induction, which bypassed the requirement for ResD for full Pho induction (35).…”

“…Reduced quinones were shown to inhibit autophosphorylation of the PhoR in vitro, suggesting that it was the ResD role in terminal oxidase production that positively modulates the PhoR signal (35) upstream of PhoPR. Consistent with this idea, resD mutants containing a spontaneous mutation in rex (formerly ydiH), a repressor of cydABCD encoding bd oxidase (34), allowed expression of cydABCD during Pho induction, which bypassed the requirement for ResD for full Pho induction (35). Together, these data indicate that the terminal oxidase bd, encoded by cydABCD, was sufficient to replace the loss of caa 3 and aa 3 in the resD mutant strain by restoring the terminal oxidase function of oxidation of reduced quinones that inhibit PhoR autophosphorylation.…”

“…P A3 is more strongly induced in vivo than in vitro, probably because it lacks an unknown activator required to compensate for its poor Ϫ35 consensus (27). To date, we have accumulated data that uncover layers of regulation placed on the Pho response by exploring the ResDE TCS, CcpA, and Spo0AϳP (19,27,32,35), but how transition state regulators affect the Pho response in B. subtilis during transition from late exponential growth to the early stationary phase (when P i concentration is Ͻ0.1 mM) (21) remains a question. AbrB binds extensively to the phoPR operon promoter region (M. A. Strauch and F. M. Hulett, unpublished data).…”

CcpA Causes Repression of the phoPR Promoter through a Novel Transcription Start Site, P A6

“…A resD-abrB double mutant is incapable of inducing Pho regulon genes upon phosphate starvation (54). The role of ResD is indirect via its essential role in the production of a-type terminal oxidases that oxidize reduced quinones that were shown to inhibit PhoR autophosphorylation in vitro (50), suggesting that ResD is required for modulation of the Pho signal. The role of AbrB remains unclear, but extensive protection of the phoPR promoter region by AbrB suggests that it may have a direct role in phoPR transcription (M. Strauch and F. M. Hulett, unpublished data).…”

Virulence Gene Expression Is Independent of ResDE-Regulated Respiration Control inBacillus anthracis

“…One explanation for the difference in these findings from those of Vetter and Schlievert (26) may stem from the propensity of resD deletion strains in all species to accumulate compensatory mutations that spontaneously appear as faster-growing opaque papillae when resD strains are grown on media without glucose. In B. subtilis, resD deletion strains spontaneously develop compensatory mutations, some of which upregulate the expression of cytochrome bd, an alternative terminal oxidase not requiring expression of the ResD-regulated ctaA gene (20)(21)(22).…”