Ppx1 putative exopolyphosphatase is essential for polyphosphate accumulation in Lacticaseibacillus paracasei

The linear polymer polyphosphate (poly-P) is present across all three domains of life and serves diverse physiological functions. The enzyme polyphosphate kinase (Ppk) is responsible for poly-P synthesis, whereas poly-P degradation is carried out by the enzyme exopolyphosphatase (Ppx). In many Lactobacillaceae, the Ppk-encoding gene (ppk) is found clustered together with two genes encoding putative exopolyphosphatases (ppx1 and ppx2) each having different domain compositions, with the gene order ppx1-ppk-ppx2. However, the specific function of these ppx genes remains unexplored. An in-frame deletion of ppx1 in Lacticaseibacillus paracasei BL23 resulted in bacteria unable to accumulate poly-P, whereas the disruption of ppx2 did not affect poly-P synthesis. The expression of ppk was not altered in the Δppx1 strain, and poly-P synthesis in this strain was only restored by expressing ppx1 in trans. Moreover, no poly-P synthesis was observed when ppk was expressed from a plasmid in the Δppx1 strain. Purified Ppx2 exhibited in vitro exopolyphosphatase activity, whereas no in vitro enzymatic activity could be demonstrated for Ppx1. This observation corresponds with the absence in Ppx1 of conserved motifs essential for catalysis found in characterized exopolyphosphatases. Furthermore, assays with purified Ppk and Ppx1 evidenced that Ppx1 enhanced Ppk activity. These results demonstrate that Ppx1 is essential for poly-P synthesis in Lc. paracasei and have unveiled, for the first time, an unexpected role of Ppx1 exopolyphosphatase in poly-P synthesis.IMPORTANCEPoly-P is a pivotal molecular player in bacteria, participating in a diverse array of processes ranging from stress resilience to pathogenesis while also serving as a functional component in probiotic bacteria. The synthesis of poly-P is tightly regulated, but the underlying mechanisms remain incompletely elucidated. Our study sheds light on the distinctive role played by the two exopolyphosphatases (Ppx) found in the Lactobacillaceae bacterial group, of relevance in food and health. This particular group is noteworthy for possessing two Ppx enzymes, supposedly involved in poly-P degradation. Remarkably, our investigation uncovers an unprecedented function of Ppx1 in Lacticaseibacillus paracasei, where its absence leads to the total cessation of poly-P synthesis, paralleling the impact observed upon eliminating the poly-P forming enzyme, poly-P kinase. Unlike the anticipated role as a conventional exopolyphosphatase, Ppx1 demonstrates an unexpected function. Our results added a layer of complexity to our understanding of poly-P dynamics in bacteria.

Loss of LasR function leads to decreased repression of Pseudomonas aeruginosa PhoB activity at physiological phosphate concentrations

While the Pseudomonas aeruginosa LasR transcription factor plays a role in quorum sensing (QS) across phylogenetically-distinct lineages, isolates with loss-of-function mutations in lasR (LasR- strains) are commonly found in diverse settings including infections where they are associated with worse clinical outcomes. In LasR- strains, the transcription factor RhlR, which is controlled by LasR, can be alternately activated in low inorganic phosphate (Pi) concentrations via the two-component system PhoR-PhoB. Here, we demonstrate a new link between LasR and PhoB in which the absence of LasR increases PhoB activity at physiological Pi concentrations and raises the Pi concentration necessary for PhoB inhibition. PhoB activity was also less repressed by Pi in mutants lacking different QS regulators (RhlR and PqsR) and in mutants lacking genes required for the production of QS-regulated phenazines suggesting that decreased phenazine production was one reason for decreased PhoB repression by Pi in LasR- strains. In addition, the CbrA-CbrB two-component system, which is elevated in LasR- strains, was necessary for reduced PhoB repression by Pi and a Δcrc mutant, which lacks the CbrA-CbrB-controlled translational repressor, activated PhoB at higher Pi concentrations than the wild type. The ΔlasR mutant had a PhoB-dependent growth advantage in a medium with no added Pi and increased virulence-determinant gene expression in a medium with physiological Pi, in part through reactivation of QS. This work suggests PhoB activity may contribute to the virulence of LasR- P. aeruginosa and subsequent clinical outcomes.

Identifying the suite of genes central to swimming in the biocontrol bacterium Pseudomonas protegens Pf-5

Swimming motility is a key bacterial trait, important to success in many niches. Biocontrol bacteria, such as Pseudomonas protegens Pf-5, are increasingly used in agriculture to control crop diseases, where motility is important for colonization of the plant rhizosphere. Swimming motility typically involves a suite of flagella and chemotaxis genes, but the specific gene set employed for both regulation and biogenesis can differ substantially between organisms. Here we used transposon-directed insertion site sequencing (TraDIS), a genome-wide approach, to identify 249 genes involved in P. protegens Pf-5 swimming motility. In addition to the expected flagella and chemotaxis, we also identified a suite of additional genes important for swimming, including genes related to peptidoglycan turnover, O-antigen biosynthesis, cell division, signal transduction, c-di-GMP turnover and phosphate transport, and 27 conserved hypothetical proteins. Gene knockout mutants and TraDIS data suggest that defects in the Pst phosphate transport system lead to enhanced swimming motility. Overall, this study expands our knowledge of pseudomonad motility and highlights the utility of a TraDIS-based approach for analysing the functions of thousands of genes. This work sets a foundation for understanding how swimming motility may be related to the inconsistency in biocontrol bacteria performance in the field.

Pseudomonas aeruginosa kills Staphylococcus aureus in a polyphosphate-dependent manner

Due to their frequent coexistence in many polymicrobial infections, including in patients with burn or chronic wounds or cystic fibrosis, recent studies have started to investigate the mechanistic details of the interaction between the opportunistic pathogens Pseudomonas aeruginosa and Staphylococcus aureus. P. aeruginosa rapidly outcompetes S. aureus under in vitro co-cultivation conditions, which is mediated by several of P. aeruginosa's virulence factors. Here, we report that polyphosphate (polyP), an efficient stress defense system and virulence factor in P. aeruginosa, plays a role for the pathogen's ability to inhibit and kill S. aureus in a contact-independent manner. We show that P. aeruginosa cells characterized by low polyP level are less detrimental to S. aureus growth and survival while the gram-positive pathogen is significantly more compromised by the presence of P. aeruginosa cells that produce high level of polyP. We show that the polyP-dependent phenotype could be a direct effect by the biopolymer, as polyP is present in the spent media and causes significant damage to the S. aureus cell envelope. However, more likely is that polyP's effects are indirect through the regulation of one of P. aeruginosa's virulence factors, pyocyanin. We show that pyocyanin production in P. aeruginosa occurs polyP-dependent and harms S. aureus through membrane damage and the generation of reactive oxygen species, resulting in increased expression of antioxidant enzymes. In summary, our study adds a new component to the list of biomolecules that the gram-negative pathogen P. aeruginosa generates to compete with S. aureus for resources.

Acinetobacter baumannii adaptation to the host pH microenvironment is mediated by allelic variation in a single residue of BauA protein

Acinetobacter baumannii has been listed as one of the most critical pathogens in nosocomial infections; however, the key genes and mechanisms to adapt to the host microenvironment lack in-depth understanding. In this study, a total of 76 isolates (from 8 to 12 isolates per patient, spanning 128 to 188 days) were longitudinally collected from eight patients to investigate the within-host evolution of A. baumannii. A total of 70 within-host mutations were identified, 80% of which were nonsynonymous, indicating the important role of positive selection. Several evolutionary strategies of A. baumannii to increase its potential to adapt to the host microenvironment were identified, including hypermutation and recombination. Six genes were mutated in isolates from two or more patients, including two TonB-dependent receptor genes (bauA and BJAB07104_RS00665). In particular, the siderophore receptor gene bauA was mutated in multiple isolates from four patients with three MLST types, and all mutations were at amino acid 391 in ligand-binding sites. With 391T or 391A, BauA was more strongly bound to siderophores, which promoted the iron-absorption activity of A. baumannii at acidic or neutral pH, respectively. Through the A/T mutation at site 391 of BauA, A. baumannii displayed two reversible phases to adapt to distinct pH microenvironments. In conclusion, we demonstrated the comprehensive within-host evolutionary dynamics of A. baumannii, and discovered a key mutation of BauA site 391 as a genetic switch to adapt to different pH values, which may represent a model in the pathogen evolutionary adaption of the host microenvironment.

SPREAD: An ensemble predictor based on DNA autoencoder framework for discriminating promoters in Pseudomonas aeruginosa

Regulatory elements in DNA sequences, such as promoters, enhancers, terminators and so on, are essential for gene expression in physiological and pathological processes. A promoter is the specific DNA sequence that is located upstream of the coding gene and acts as the "switch" for gene transcriptional regulation. Lots of promoter predictors have been developed for different bacterial species, but only a few are designed for Pseudomonas aeruginosa, a widespread Gram-negative conditional pathogen in nature. In this work, an ensemble model named SPREAD is proposed for the recognition of promoters in Pseudomonas aeruginosa. In SPREAD, the DNA sequence autoencoder model LSTM is employed to extract potential sequence information, and the mean output probability value of CNN and RF is applied as the final prediction. Compared with G4PromFinder, the only state-of-the-art classifier for promoters in Pseudomonas aeruginosa, SPREAD improves the prediction performance significantly, with an accuracy of 0.98, recall of 0.98, precision of 0.98, specificity of 0.97 and F1-score of 0.98.

Decoding Acinetobacter baumannii biofilm dynamics and associated protein markers: proteomic and bioinformatics approach

Biofilm formation by Acinetobacter baumannii is one of the major cause of its persistence in hospital environment. Biofilm phenotypes are more resistant to physical as well as chemical stresses than their planktonic counterparts. The present study was carried in quest of biofilm-associated protein markers and their association with various biological pathways of A. baumannii. The study was designed with an aim to highlight the crucial common factor present in the majority of the A. baumannii strains irrespective of its resistance nature. A label-free proteome comparison of biofilm and planktonic phenotypes of A. baumannii was done using QExactive tandem mass spectrometry. Our investigation suggests key elevation of adhesion factors, acetate metabolism, nutrient transporters, and secretion system proteins are required for biofilm formation in A. baumannii. Elevation of biofilm-associated proteins revealed that biofilm is the unique phenotype with the potential to form robust matrix-embedded colonies and defeat stress condition. Further, core protein markers of biofilm phenotypes could be used as targets for new clinical interventions to combat biofilm-associated infections.

The Regulatory Hierarchy Following Signal Integration by the CbrAB Two-Component System: Diversity of Responses and Functions

CbrAB is a two-component system, unique to bacteria of the family Pseudomonaceae, capable of integrating signals and involved in a multitude of physiological processes that allow bacterial adaptation to a wide variety of varying environmental conditions. This regulatory system provides a great metabolic versatility that results in excellent adaptability and metabolic optimization. The two-component system (TCS) CbrA-CbrB is on top of a hierarchical regulatory cascade and interacts with other regulatory systems at different levels, resulting in a robust output. Among the regulatory systems found at the same or lower levels of CbrAB are the NtrBC nitrogen availability adaptation system, the Crc/Hfq carbon catabolite repression cascade in Pseudomonas, or interactions with the GacSA TCS or alternative sigma ECF factor, such as SigX. The interplay between regulatory mechanisms controls a number of physiological processes that intervene in important aspects of bacterial adaptation and survival. These include the hierarchy in the use of carbon sources, virulence or resistance to antibiotics, stress response or definition of the bacterial lifestyle. The multiple actions of the CbrAB TCS result in an important competitive advantage.

The structure of exopolyphosphatase (PPX) from Porphyromonas gingivalis in complex with substrate analogs and magnesium ions reveals the basis for polyphosphate processivity

The enzymes exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (PPX/GppA) play important roles in the bacterial stringent response. PPX degrades inorganic polyphosphate (polyP), a polymer composed of a few to hundreds of phosphate residues supporting cell survival in the stationary phase. The crystal structure of PPX from Porphyromonas gingivalis (PgPPX) in complex with catalytic magnesium ions and several sulfate ions was solved. PgPPX contained two domains and represented a "closed" configuration. Four sulfate ions forming a linear dispersed chain were observed in the aqueduct of the PPX dimer, which the long polyP chain most likely occupied. The side chain of R255 stretched into the cavity where polyP could be located, obstructing the entrance of larger substrates such as NTP and NDP. This study provided the first view into the structure of the PPX/GppA homolog in complex with magnesium ions and substrate analogs and explained how PgPPX implemented its functionality.

A Dual-Specificity Inhibitor Targets Polyphosphate Kinase 1 and 2 Enzymes To Attenuate Virulence of Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa is a leading cause of nosocomial infections, which are becoming increasingly difficult to treat due to antibiotic resistance. Polyphosphate (polyP) plays a key role in P. aeruginosa virulence, stress response, and antibiotic tolerance, suggesting an attractive drug target. Here, we show that the small molecule gallein disrupts polyphosphate homeostasis by inhibiting all members of both polyphosphate kinase (PPK) families (PPK1 and PPK2) encoded by P. aeruginosa, demonstrating dual-specificity PPK inhibition for the first time. Inhibitor treatment phenocopied ppk deletion to reduce cellular polyP accumulation and attenuate biofilm formation, motility, and pyoverdine and pyocyanin production. Most importantly, gallein attenuated P. aeruginosa virulence in a Caenorhabditis elegans infection model and synergized with antibiotics while exhibiting negligible toxicity toward the nematodes or HEK293T cells, suggesting our discovery of dual-specificity PPK inhibitors as a promising starting point for the development of new antivirulence therapeutics.

A Novel Small RNA Promotes Motility and Virulence of Enterohemorrhagic Escherichia coli O157:H7 in Response to Ammonium

The process by which bacteria sense environmental cues to regulate their virulence is complex. Several studies have focused on regulating the expression of the locus of enterocyte effacement pathogenicity island in the typical gut pathogenic bacterium, O157.

Enterohemorrhagic Escherichia coli serotype O157:H7 (O157) is a critical, foodborne, human intestinal pathogen that causes severe acute hemorrhagic diarrhea, abdominal cramping, and even death. Small RNAs (sRNAs) are noncoding regulatory molecules that sense environmental changes and trigger various virulence-related signaling pathways; however, few such sRNAs have been identified in O157. Here, we report a novel sRNA, EsrF that senses high ammonium concentrations in the colon and enhances O157 pathogenicity by promoting bacterial motility and adhesion to host cells. Specifically, EsrF was found to directly interact with the 5′ untranslated regions of the flagellar biosynthetic gene, flhB, mRNA and increase its abundance, thereby upregulating expression of essential flagellar genes, including flhD, flhC, fliA, and fliC, leading to elevated O157 motility and virulence. Meanwhile, an infant rabbit model of O157 infection showed that deletion of esrF and flhB significantly attenuates O157 pathogenicity. Furthermore, NtrC—the response regulator of the NtrC/B two-component system—was found to exert direct, negative regulation of esrF expression. Meanwhile, high ammonium concentrations in the colon release the inhibitory effect of NtrC on esrF, thereby enhancing its expression and subsequently promoting bacterial colonization in the host colon. Our work reveals a novel, sRNA-centered, virulence-related signaling pathway in O157 that senses high ammonium concentrations. These findings provide novel insights for future research on O157 pathogenesis and targeted treatment strategies.

Model systems for studying polyphosphate biology: a focus on microorganisms

Polyphosphates (polyP) are polymers of inorganic phosphates joined by high-energy bonds to form long chains. These chains are present in all forms of life but were once disregarded as 'molecular fossils'. PolyP has gained attention in recent years following new links to diverse biological roles ranging from energy storage to cell signaling. PolyP research in humans and other higher eukaryotes is limited by a lack of suitable tools and awaits the identification of enzymatic players that would enable more comprehensive studies. Therefore, many of the most important insights have come from single-cell model systems. Here, we review determinants of polyP metabolism, regulation, and function in major microbial systems, including bacteria, fungi, protozoa, and algae. We highlight key similarities and differences that may aid in our understanding of how polyP impacts cell physiology at a molecular level.

Attenuation of Acinetobacter baumannii virulence by inhibition of polyphosphate kinase 1 with repurposed drugs

Acinetobacter baumannii is clinically one of the most significant pathogens, especially in intensive care settings, because of its multidrug-resistance (MDR). Repurposing of high-affinity drugs is a faster and more plausible approach for combating the emergence of MDR and to tackle bacterial infections. This study was aimed to evaluate the approved drugs potentially inhibiting A. baumannii PPK1 (AbPPK1) mediated synthesis of polyphosphates (polyP). Based on virtual screening, molecular dynamic simulation, and CD spectroscopy for thermal stability, two stable ligands, etoposide and genistein, were found with promising contours for further investigation. Following in vitro inhibition of AbPPK1, the efficacy of selected drugs was further tested against virulence traits of A. baumannii. These drugs significantly reduced the biofilm formation, surface motility in A. baumannii and led to decreased survival under desiccation. In addition to inhibition of PPK1, both drugs increased the expression of polyP degrading enzyme, exopolyphosphatase (PPX), that might be responsible for the decrease in the total cellular polyP. Since polyP modulates the virulence factors in bacteria, destabilization of the polyP pool by these drugs seems particularly striking for their therapeutic applications against A. baumannii.

The potential for polyphosphate metabolism in Archaea and anaerobic polyphosphate formation in Methanosarcina mazei

Inorganic polyphosphate (polyP) is ubiquitous across all forms of life, but the study of its metabolism has been mainly confined to bacteria and yeasts. Few reports detail the presence and accumulation of polyP in Archaea, and little information is available on its functions and regulation. Here, we report that homologs of bacterial polyP metabolism proteins are present across the major taxa in the Archaea, suggesting that archaeal populations may have a greater contribution to global phosphorus cycling than has previously been recognised. We also demonstrate that polyP accumulation can be induced under strictly anaerobic conditions, in response to changes in phosphate (Pi) availability, i.e. Pi starvation, followed by incubation in Pi replete media (overplus), in cells of the methanogenic archaeon Methanosarcina mazei. Pi-starved M. mazei cells increased transcript abundance of the alkaline phosphatase (phoA) gene and of the high-affinity phosphate transport (pstSCAB-phoU) operon: no increase in polyphosphate kinase 1 (ppk1) transcript abundance was observed. Subsequent incubation of Pi-starved M. mazei cells under Pi replete conditions, led to a 237% increase in intracellular polyphosphate content and a > 5.7-fold increase in ppk1 gene transcripts. Ppk1 expression in M. mazei thus appears not to be under classical phosphate starvation control.

Stringent Response Factors PPX1 and PPK2 Play an Important Role in Mycobacterium tuberculosis Metabolism, Biofilm Formation, and Sensitivity to Isoniazid In Vivo

Mycobacterium tuberculosis remains a global health threat largely due to the lengthy duration of curative antibiotic treatment, contributing to medical nonadherence and the emergence of drug resistance. This prolonged therapy is likely due to the presence of M. tuberculosis persisters, which exhibit antibiotic tolerance. Inorganic polyphosphate [poly(P)] is a key regulatory molecule in the M. tuberculosis stringent response mediating antibiotic tolerance. The polyphosphate kinase PPK1 is responsible for poly(P) synthesis in M. tuberculosis, while the exopolyphosphatases PPX1 and PPX2 and the GTP synthase PPK2 are responsible for poly(P) hydrolysis. In the present study, we show by liquid chromatography-tandem mass spectrometry that poly(P)-accumulating M. tuberculosis mutant strains deficient in ppx1 or ppk2 had significantly lower intracellular levels of glycerol-3-phosphate (G3P) and 1-deoxy-xylulose-5-phosphate. Real-time PCR revealed decreased expression of genes in the G3P synthesis pathway in each mutant. The ppx1-deficient mutant also showed a significant accumulation of metabolites in the tricarboxylic acid cycle, as well as altered arginine and NADH metabolism. Each poly(P)-accumulating strain showed defective biofilm formation, while deficiency of ppk2 was associated with increased sensitivity to plumbagin and meropenem and deficiency of ppx1 led to enhanced susceptibility to clofazimine. A DNA vaccine expressing ppx1 and ppk2, together with two other members of the M. tuberculosis stringent response, M. tuberculosis rel and sigE, did not show protective activity against aerosol challenge with M. tuberculosis, but vaccine-induced immunity enhanced the killing activity of isoniazid in a murine model of chronic tuberculosis. In summary, poly(P)-regulating factors of the M. tuberculosis stringent response play an important role in M. tuberculosis metabolism, biofilm formation, and antibiotic sensitivity in vivo.

Differential regulation of polyphosphate genes in Pseudomonas aeruginosa

Phosphate homeostasis is tightly regulated in bacteria. Phosphate scarcity is overcome by inducing the expression of genes associated with the scavenging of phosphate and phosphate-containing molecules, while phosphate surplus is stored in the form of polyphosphate (polyP). Regulation of the genes involved in polyP metabolism was investigated. Knockout of the most distal gene of the pstSCAB-phoU operon that encodes a Pi-transport system results in large accumulation of polyphosphate (polyP). Here, we show that the phoU mutation differentially affects the transcription of ppk and ppx, that respectively, encode a polyP kinase and a polyP exopolyphosphatase, by increasing the former and reducing the latter, further contributing the accumulation of polyP. We also show that ppk forms an operon with the upstream gene hemB and that neither ppk nor ppx positively respond to Pi starvation. Furthermore, a putative PHO-box sequence in ppx regulatory region did not show a strong affinity for the PHO response regulator PhoB, while the promoter of hemB does not carry a PHO-box sequence. Altogether, the data indicate that the main genes involved in polyP metabolism, ppk and ppx, are differentially regulated in the absence of phoU, but neither gene belongs to the PHO regulon.

Putative binding mode of Escherichia coli exopolyphosphatase and polyphosphates based on a hybrid in silico/biochemical approach

The exopolyphosphatase of Escherichia coli processively and completely hydrolyses long polyphosphate chains to ortho-phosphate. Genetic surveys, based on the analysis of single ppx(-) or ppk(-) mutants and on the double mutant, demonstrate a relationship between these genes and the survival capacity. The exopolyphosphatase belongs to the ASKHA protein superfamily, hence, its active site is well known; however, the knowledge of the way in which this enzyme binds polyP remains incomplete. Here we present different computational approaches, site-direct mutagenesis and kinetic data to understand the relationship between structure and function of exopolyphosphatase. We propose H(378) as a fundamental gatekeeper for the recognition of long chain polyphosphate.

Purification, crystallization and X-ray crystallographic analysis of a putative exopolyphosphatase from Zymomonas mobilis

Exopolyphosphatase (PPX) enzymes degrade inorganic polyphosphate (poly-P), which is essential for the survival of microbial cells in response to external stresses. In this study, a putative exopolyphosphatase from Zymomonas mobilis (ZmPPX) was crystallized. Crystals of the wild-type enzyme diffracted to 3.3 Å resolution and could not be optimized further. The truncation of 29 amino acids from the N-terminus resulted in crystals that diffracted to 1.8 Å resolution. The crystals belonged to space group C2, with unit-cell parameters a = 122.0, b = 47.1, c = 89.5 Å, α = γ = 90, β = 124.5°. An active-site mutant that crystallized in the same space group and with similar unit-cell parameters diffracted to 1.56 Å resolution. One molecule was identified per asymmetric unit. Analytical ultracentrifugation confirmed that ZmPPX forms a dimer in solution. It was confirmed that ZmPPX possesses exopolyphosphatase activity against a synthetic poly-P substrate.

Pseudomonas aeruginosa Exopolyphosphatase Is Also a Polyphosphate: ADP Phosphotransferase

Pseudomonas aeruginosa exopolyphosphatase (paPpx; EC 3.6.1.11) catalyzes the hydrolysis of polyphosphates (polyP), producing polyP_n−1 plus inorganic phosphate (P_i). In a recent work we have shown that paPpx is involved in the pathogenesis of P. aeruginosa. The present study was aimed at performing the biochemical characterization of this enzyme. We found some properties that were already described for E. coli Ppx (ecPpx) but we also discovered new and original characteristics of paPpx: (i) the peptide that connects subdomains II and III is essential for enzyme activity; (ii) NH₄⁺ is an activator of the enzyme and may function at concentrations lower than those of K⁺; (iii) Zn²⁺ is also an activator of paPpx and may substitute Mg²⁺ in the catalytic site; and (iv) paPpx also has phosphotransferase activity, dependent on Mg²⁺ and capable of producing ATP regardless of the presence or absence of K⁺ or NH₄⁺ ions. In addition, we detected that the active site responsible for the phosphatase activity is also responsible for the phosphotransferase activity. Through the combination of molecular modeling and docking techniques, we propose a model of the paPpx N-terminal domain in complex with a polyP chain of 7 residues long and a molecule of ADP to explain the phosphotransferase activity.

phoU inactivation in Pseudomonas aeruginosa enhances accumulation of ppGpp and polyphosphate

Inorganic polyphosphate (polyP) is a linear polymer composed of several molecules of orthophosphate (Pi) linked by energy-rich phosphoanhydride bonds. In Pseudomonas aeruginosa, Pi is taken up by the ABC transporter Pst, encoded by an operon consisting of five genes. The first four genes encode proteins involved in the transport of Pi and the last gene of the operon, phoU, codes for a protein which exact function is unknown. We show here that the inactivation of phoU in P. aeruginosa enhanced Pi removal from the medium and polyP accumulation. The phoU mutant also accumulated high levels of the alarmone guanosine tetraphosphate (ppGpp), which in turn increased the buildup of polyP. In addition, phoU inactivation had several pleiotropic effects, such as reduced growth rate and yield and increased sensitivity to antibiotics and stresses. However, biofilm formation was not affected by the phoU mutation.