Broad-Spectrum Inhibitor of Bacterial Polyphosphate Homeostasis Attenuates Virulence Factors and Helps Reveal Novel Physiology of Klebsiella pneumoniae and Acinetobacter baumannii

Two endogenous Dictyostelium discoideum chemorepellents use different mechanisms to induce repulsion

The directed movement of eukaryotic cells is critical for processes such as development and immune responses. While much is known about chemoattraction, much less is known about chemorepulsion. The eukaryotic amoeba Dictyostelium discoideum secretes a 60 kDa chemorepellent protein called AprA to cause cells at the edge of a colony to move away from the colony. In addition to AprA, cells secrete a <10 kDa chemorepellent. Here, we show that the <10 kDa chemorepellent is a polymer of phosphates (polyphosphate; polyP). D. discoideum cells move by activating cortical Ras at one edge of the cell to initiate pseudopod formation. AprA induces repulsion by inhibiting Ras activation and pseudopod formation on the side of the cell closest to the source of AprA, without affecting the overall frequency of pseudopod formation. In contrast, polyP activates Ras at multiple regions of the cortex and increases pseudopod formation frequency, especially at the side of the cell furthest from the source of polyP. At least 20 signal transduction proteins are needed for both AprA and polyP repulsion, 9 are needed by polyP but not AprA, and 4 are needed by AprA but not polyP. Together, these results indicate that proliferating D. discoideum cells use two different chemorepellents, that one of the repellents is the unusual molecule polyphosphate, and that the two repellents activate partially overlapping and partially different pathways to induce repulsion by two basically different mechanisms.

Current and novel therapies for management of Acinetobacter baumannii-associated pneumonia

Acinetobacter baumannii is a common pathogen associated with hospital-acquired pneumonia showing increased resistance to carbapenem and colistin antibiotics nowadays. Infections with A. baumannii cause high patient fatalities due to their capability to evade current antimicrobial therapies, emphasizing the urgency of developing viable therapeutics to treat A. baumannii-associated pneumonia. In this review, we explore current and novel therapeutic options for overcoming therapeutic failure when dealing with A. baumannii-associated pneumonia. Among them, antibiotic combination therapy administering several drugs simultaneously or alternately, is one promising approach for optimizing therapeutic success. However, it has been associated with inconsistent and inconclusive therapeutic outcomes across different studies. Therefore, it is critical to undertake additional clinical trials to ascertain the clinical effectiveness of different antibiotic combinations. We also discuss the prospective roles of novel antimicrobial therapies including antimicrobial peptides, bacteriophage-based therapy, repurposed drugs, naturally-occurring compounds, nanoparticle-based therapy, anti-virulence strategies, immunotherapy, photodynamic and sonodynamic therapy, for utilizing them as additional alternative therapy while tackling A. baumannii-associated pneumonia. Importantly, these innovative therapies further require pharmacokinetic and pharmacodynamic evaluation for safety, stability, immunogenicity, toxicity, and tolerability before they can be clinically approved as an alternative rescue therapy for A. baumannii-associated pulmonary infections.

Pharmacological inhibition of host pathways enhances macrophage killing of intracellular bacterial pathogens

After ingestion into macrophage phagosomes, some bacterial pathogens such as Mycobacterium tuberculosis ( Mtb ) evade killing by preventing phagosome acidification and fusion of the phagosome with a lysosome. Mtb accumulates extracellular polyphosphate (polyP), and polyP inhibits macrophage phagosome acidification and bacterial killing. In Dictyostelium discoideum , polyP also inhibits bacterial killing, and we identified some proteins in D. discoideum that polyP requires to suppress the killing of ingested bacteria. Here, we find that pharmacological inhibition of human orthologues of the D. discoideum proteins, including P2Y1 receptors, mammalian Target of Rapamycin (mTOR), and inositol hexakisphosphate kinase, enhances the killing of Mtb , Legionella pneumophila , and Listeria monocytogenes by human macrophages. Mtb inhibits phagosome acidification, expression of the proinflammatory marker CD54, and autophagy, and increases expression of the anti-inflammatory marker CD206. In Mtb -infected macrophages, the polyP-degrading enzyme polyphosphatase (ScPPX) and inhibitors reversed these effects, with ScPPX increasing CD54 expression more in female macrophages compared to male macrophages. In addition, Mtb inhibits proteasome activity, and some, but not all, inhibitors reversed these effects. While the existence of a dedicated polyP signaling pathway remains uncertain, our findings suggest that pharmacological inhibition of select host proteins can restore macrophage function and enhances the killing of intracellular pathogens.

Importance

Human macrophages engulf bacteria into phagosomes, which then fuse with lysosomes to kill the bacteria. However, after engulfment, pathogenic bacteria such as Mycobacterium tuberculosis , Legionella pneumophila , and Listeria monocytogenes can block phagosome-lysosome fusion, allowing their survival. Here, we show that pharmacological inhibition of specific macrophage proteins reverses these effects and enhances bacterial killing. These findings suggest that targeting host factors involved in these processes may provide a therapeutic strategy to improve macrophage function against infections such as tuberculosis, Legionnaires' disease, and listeriosis.

A Novel Silver-Ruthenium-Based Antimicrobial Kills Gram-Negative Bacteria Through Oxidative Stress-Induced Macromolecular Damage

Amplified by the decline in antibiotic discovery, the rise of antibiotic resistance has become a significant global challenge in infectious disease control. Extraintestinal Escherichia coli (ExPEC), known to be the most common instigators of urinary tract infections (UTIs), represent such global threat. Novel strategies for more efficient treatments are therefore desperately needed. These include silver nanoparticles, which have been used as antimicrobial surface-coatings on catheters to eliminate biofilm-forming uropathogens and reduce the risk of nosocomial infections. AGXX® is a promising silver coating that presumably kills bacteria through the generation of reactive oxygen species (ROS) but is more potent than silver. However, neither is AGXX®'s mode of action fully understood, nor have its effects on Gram-negative bacteria or bacterial response and defense mechanisms towards AGXX® been studied in detail. Here, we report that the bactericidal effects of AGXX® are primarily based on ROS formation, as supplementation of the media with a ROS scavenger completely abolished AGXX®-induced killing. We further show that AGXX® impairs the integrity of the bacterial cell envelope and causes substantial protein aggregation and DNA damage already at sublethal concentrations. ExPEC strains appear to be more resistant to the proteotoxic effects of AGXX® compared to non-pathogenic E. coli, indicating improved defense capabilities of the uropathogen. Global transcriptomic studies of AGXX®-stressed ExPEC revealed a strong oxidative stress response, perturbations in metal homeostasis, as well as the activation of heat shock and DNA damage responses. Finally, we present evidence that ExPEC counter AGXX® damage through the production of the chaperone polyphosphate.

Fluoride and gallein regulate polyphosphate accumulation in dental caries-associated Lacticaseibacillus

Inorganic polyphosphates (polyPs) are energy-storing biopolymers synthesized by all three domains of life. PolyP accumulation has been well studied with respect to its role in stress response, but its role in dental disease has received less attention. Dental decay can be promoted by changes in pH as well as the chemical activity of ions such as phosphate in oral fluids at the enamel interface. Previous work has shown that the drawdown of phosphate from biofilm fluids can alter the saturation state of oral fluids to thermodynamically favour mineral dissolution. The members of the Lactobacillaceae are known to accumulate polyP and play a role in early-stage and late-stage dental caries. In this study, we examined the effects of potential metabolic inhibitors on polyP accumulation in Lacticaseibacillus rhamnosus. We observed that two inhibitors of the enzyme responsible for polyP synthesis, gallein and fluoride, inhibited polyP accumulation in a balanced medium. However, fluoride and gallein treatments amended with either glucose or lactate were found to enhance polyP accumulation. These results illustrate the potential complexity of polyP metabolism in the oral environment.

Pseudomonas aeruginosa kills Staphylococcus aureus in a polyphosphate-dependent manner

Due to their frequent coexistence in many polymicrobial infections, including in patients with cystic fibrosis or burn/chronic wounds, many studies have investigated the mechanistic details of the interaction between the opportunistic pathogens Pseudomonas aeruginosa and Staphylococcus aureus. P. aeruginosa rapidly outcompetes S. aureus under in vitro cocultivation 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 in 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 levels 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 levels of polyP. The polyP-dependent phenotype of P. aeruginosa-mediated killing of S. aureus could at least in part be direct, as polyP was detected 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 modulating the production of one of P. aeruginosa's virulence factors, pyocyanin. We show that pyocyanin production in P. aeruginosa occurs polyP-dependently and harms S. aureus through membrane damage and potentially the generation of reactive oxygen species, resulting in the 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.IMPORTANCEHow do interactions between microorganisms shape the course of polymicrobial infections? Previous studies have provided evidence that the two opportunistic pathogens Pseudomonas aeruginosa and Staphylococcus aureus generate molecules that modulate their interaction with potentially significant impact on disease outcomes. Our study identified the biopolymer polyphosphate (polyP) as a new effector molecule that impacts P. aeruginosa's interaction with S. aureus. We show that P. aeruginosa kills S. aureus in a polyP-dependent manner, which occurs primarily through the polyP-dependent production of the P. aeruginosa virulence factor pyocyanin. Our findings add a new role for polyP to an already extensive list of functions. A more in-depth understanding of how polyP influences interspecies interactions is critical, as targeting polyP synthesis in bacteria such as P. aeruginosa may have a significant impact on other microorganisms and potentially result in dynamic changes in the microbial composition.

Comparative genome analysis reveals putative and novel antimicrobial resistance genes common to the nosocomial infection pathogens

The 21st century has witnessed several clinical outcomes regarding AMR. One health concept has been foreseen as a standard global public health initiative in ensuring human, animal and environmental health. The present study explores critical Gram-negative ESKAPE pathogens encompassing Acinetobacter baumannii (ACB), Klebsiella pneumoniae (KPX) and Pseudomonas aeruginosa (PAE). A comparative genomic analysis approach was utilized for identifying novel and putative genes coercing global health consequences stressing the significance of the above iatrogenic and nosocomial pathogens. O findings reveal that Pseudomonas aeruginosaPAO1 (PAE) possesses the largest genome, measuring 62,64,404 base pairs, containing 14,342 protein-coding genes and an elevated count of ORFs, surpassing other organisms. Notably, P. aeruginosa PAO1 exhibits a comprehensive metabolic landscape with 355 pathways and 1659 metabolic reactions, encompassing 200 biosynthesis and 132 degradation pathways. Transferases are the predominant enzyme category across all three genomes, followed by oxidoreductases and hydrolases. The pivotal role of beta-lactamase in conferring resistance against antibiotics is also evident in all three microbes. This investigation underscores the PAE genome harbours genes and enzymes associated with heightened virulence in antibiotic resistance. The holistic review combined with comparative genomics underlines the significance of delving into the genomes of these antimicrobial-resistant organisms. In silico methodologies are increasingly stressed in aiding the successful accomplishment of the United Nations Sustainable Development Goal -3: Good Health and Well-being. The prominent findings establish Carbapenem resistance and evolutionary lineages of the MCR-1 gene conferring AMR landscapes for future research.

In vitro and in vivo activities of scutellarein, a novel polyphosphate kinase 1 inhibitor against Acinetobacter baumannii infection

BACKGROUND

Inorganic polyphosphate (polyP)-targeted polyphosphate kinase 1 (PPK1) has attracted much attention by virtue of its importance in bacterial pathogenicity and persistence, as well as its exclusive presence in microorganisms. However, only very few drugs have been found to be efficacious in inhibiting the Acinetobacter baumannii (A. baumannii) PPK1 protein.

RESULTS

In this study, we identified Scutellarein (Scu), a potent PPK1 inhibitor that could significantly influence PPK1-regulated motility, biofilm formation, and bacterial persistence, which was further validated by the results of transcriptome analysis. Mechanistic explorations revealed that Scu achieved its enzyme inhibitory activity predominantly through direct engagement with the active center of PPK1. Moreover, the survival rate of Galleria mellonella larvae was increased by about 35% with 20 mg/kg of Scu treatment. The remarkable therapeutic benefits of Scu were also observed in the mouse pneumonia model, shown mainly by reduced bacterial colonization, pathological lesions, and inflammatory factors.

CONCLUSION

Our results revealed that Scu could attenuate the pathogenicity and persistence of A. baumannii by interfering with its important kinase PPK1.

Enhancing L-Asparagine Bioproduction Efficiency Through L-Asparagine Synthetase and Polyphosphate Kinase-Coupled Conversion and ATP Regeneration

L-Asparagine, a crucial amino acid widely used in both food and medicine, presents pollution-related and side reaction challenges when prepared using chemical synthesis method. Although biotransformation methods offer significant advantages such as high efficiency and mild reaction conditions, they also entail increased costs due to the need for ATP supplementation. This study aimed to address the challenges associated with biopreparation of L-asparagine. Firstly, the functionality and characteristics of recombinant L-asparagine synthetase enzymes derived from Escherichia coli and Lactobacillus salivarius were evaluated to determine their practical applicability. Subsequently, recombinant expression of polyphosphate kinase from Erysipelotrichaceae bacterium was conducted. A reaction system for L-asparagine synthesis was established using a dual enzyme-coupled conversion approach. Under the optimal reaction conditions, a maximum yield of 11.67 g/L of L-asparagine was achieved, with an 88.43% conversion rate, representing a 5.03-fold increase compared to the initial conversion conditions. Notably, the initial addition of ATP was reduced to only 5.66% of the theoretical demand, indicating the effectiveness of our ATP regeneration system. These findings highlight the potential of our approach in enhancing the efficiency of L-asparagine preparation, offering promising prospects for the food and medical industries.

C-terminal Poly-histidine Tags Alter Escherichia coli Polyphosphate Kinase Activity and Susceptibility to Inhibition

In Escherichia coli, many environmental stressors trigger polyphosphate (polyP) synthesis by polyphosphate kinase (PPK1), including heat, nutrient restriction, toxic compounds, and osmotic imbalances. PPK1 is essential for virulence in many pathogens and has been the target of multiple screens for small molecule inhibitors that might serve as new anti-virulence drugs. However, the mechanisms by which PPK1 activity and polyP synthesis are regulated are poorly understood. Our previous attempts to uncover PPK1 regulatory elements resulted in the discovery of PPK1* mutants, which accumulate more polyP in vivo, but do not produce more in vitro. In attempting to further characterize these mutant enzymes, we discovered that the most commonly-used PPK1 purification method - Ni-affinity chromatography using a C-terminal poly-histidine tag - altered intrinsic aspects of the PPK1 enzyme, including specific activity, oligomeric state, and kinetic values. We developed an alternative purification strategy using a C-terminal C-tag which did not have these effects. Using this strategy, we were able to demonstrate major differences in the in vitro response of PPK1 to 5-aminosalicylic acid, a known PPK1 inhibitor, and observed several key differences between the wild-type and PPK1* enzymes, including changes in oligomeric distribution, increased enzymatic activity, and increased resistance to both product (ADP) and substrate (ATP) inhibition, that help to explain their in vivo effects. Importantly, our results indicate that the C-terminal poly-histidine tag is inappropriate for purification of PPK1, and that any in vitro studies or inhibitor screens performed with such tags need to be reconsidered in that light.

Inorganic Polyphosphate Affects Biofilm Assembly, Capsule Formation, and Virulence of Hypervirulent ST23 Klebsiella pneumoniae

The emergence of hypervirulent Klebsiella pneumoniae (hvKP) strains poses a significant threat to public health due to high mortality rates and propensity to cause severe community-acquired infections in healthy individuals. The ability to form biofilms and produce a protective capsule contributes to its enhanced virulence and is a significant challenge to effective antibiotic treatment. Polyphosphate kinase 1 (PPK1) is an enzyme responsible for inorganic polyphosphate synthesis and plays a vital role in regulating various physiological processes in bacteria. In this study, we investigated the impact of polyP metabolism on the biofilm and capsule formation and virulence traits in hvKP using Dictyostelium discoideum amoeba as a model host. We found that the PPK1 null mutant was impaired in biofilm and capsule formation and showed attenuated virulence in D. discoideum compared to the wild-type strain. We performed a proteomic analysis to gain further insights into the underlying molecular mechanism. The results revealed that the PPK1 mutant had a differential expression of proteins involved in capsule synthesis (Wzi-Ugd), biofilm formation (MrkC-D-H), synthesis of the colibactin genotoxin precursor (ClbB), as well as proteins associated with the synthesis and modification of lipid A (ArnB-LpxC-PagP). These proteomic findings corroborate the phenotypic observations and indicate that the PPK1 mutation is associated with impaired biofilm and capsule formation and attenuated virulence in hvKP. Overall, our study highlights the importance of polyP synthesis in regulating extracellular biomolecules and virulence in K. pneumoniae and provides insights into potential therapeutic targets for treating K. pneumoniae infections.

Gallein and isoniazid act synergistically to attenuate Mycobacterium tuberculosis growth in human macrophages

Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis (TB), can be difficult to treat because of drug resistance. Increased intracellular polyphosphate (polyP) in Mtb enhances resistance to antibiotics, and capsular polyP in Neisseria gonorrhoeae potentiates resistance to antimicrobials. The mechanism by which bacteria utilize polyP to adapt to antimicrobial pressure is not known. In this study, we found that Mtb adapts to the TB frontline antibiotic isoniazid (INH) by enhancing the accumulation of cellular, extracellular, and cell surface polyP. Gallein, a broad-spectrum inhibitor of the polyphosphate kinase that synthesizes polyP, prevents this INH-induced increase in extracellular and cell surface polyP levels. Gallein and INH work synergistically to attenuate Mtb's ability to grow in in vitro culture and within human macrophages. Mtb when exposed to INH, and in the presence of INH, gallein inhibits cell envelope formation in most but not all Mtb cells. Metabolomics indicated that INH or gallein have a modest impact on levels of Mtb metabolites, but when used in combination, they significantly reduce levels of metabolites involved in cell envelope synthesis and amino acid, carbohydrate, and nucleoside metabolism, revealing a synergistic effect. These data suggest that gallein represents a promising avenue to potentiate the treatment of TB.

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.

Structural insight into substrate binding of Acinetobacter baumannii polyphosphate-AMP phosphotransferase (PPK2), a novel drug target

Acinetobacter baumannii is an opportunistic pathogen known for high morbidity and mortality. It causes life-threatening infections, such as ventilator-associated pneumonia (VAP), bacteremia, meningitis, wound and urinary tract infections (UTI). Increase in carbapenem resistance exhibited by A. baumannii has accentuated the need for novel targets for effective treatment. Despite the pronounced relevance of PPK2 as a pathogenicity determinant in several pathogens, it has not been explored as a drug target in A. baumannii. The present study was piloted to investigate the substrate binding by A. baumannii PPK2 (AbPPK2), a two-domain Class II polyphosphate kinase 2. A homology model of AbPPK2 was developed and validated for molecular docking of ATP and ADP in the predicted binding pocket. Further analysis of AbPPK2 revealed a set of common residues in the catalytic cleft interacting with ATP and ADP which would be useful for the screening of inhibitors against A. baumannii.

Polyphosphate Kinase Is Required for the Processes of Virulence and Persistence in Acinetobacter baumannii

Acinetobacter baumannii, one of the most successful bacteria causing severe nosocomial infection, was identified as a top-priority pathogen by the WHO. Thus, genetic manipulations to clarify the potential targets for fighting A. baumannii resistance and virulence are vital. Polyphosphate (polyP) kinase (PPK) is conserved in nearly all bacteria and is responsible for polyP formation, which is associated with bacterial pathogenicity and antibiotic resistance. In this study, ppk1-deficient (Δppk1::Apr), ppk1-complemented (Δppk1::Apr/PJL02-ppk1), and wild-type strains of A. baumannii ATCC 17978 were used to determine the influence of PPK1 on A. baumannii virulence and persistence mainly by polyP quantification, surface motility, biofilm formation, and bacterial persistence assays. Our work found that PPK1 is indispensable for polyP formation in vivo and that the motility of the PPK1-deficient strain was significantly impaired due to the lack of a pilus-like structure typically present compared with the complemented and wild-type strains. The deficiency of PPK1 also inhibited the biofilm formation of A. baumannii and decreased bacterial persistence under stimuli of high-concentration ampicillin (Amp) treatment, H₂O₂ stress, heat shock, and starvation stress. Furthermore, ppk1-deficient bacterium-infected mice showed a significantly reduced bacterial load and a decreased inflammatory response. However, complementation with PPK1 effectively rescued the impaired virulence and persistence of ppk1-deficient A. baumannii. In addition, metabonomic analysis revealed that PPK1 was associated with glycerophospholipid metabolism and fatty acid biosynthesis. Taken together, our results suggest that targeting PPK1 to control A. baumannii pathogenicity and persistence is a feasible strategy to fight this pathogen.

IMPORTANCEA. baumannii was identified as a top-priority pathogen by the WHO due to its antibiotic resistance. Meanwhile, the pathogenicity of A. baumannii mediated by several vital virulence factors also cannot be ignored. Here, the role of PPK1 in A. baumannii was also explored. We found that the motility ability and biofilm formation of a PPK1-deficient strain were significantly impaired. Furthermore, PPK1 was essential for its persistence maintenance to resist stimuli of high-concentration Amp treatment, H₂O₂ stress, heat shock, and starvation stress. Metabonomic analysis revealed that PPK1 was associated with glycerophospholipid metabolism and fatty acid biosynthesis. In addition, ppk1-deficient bacterium-infected mice showed significantly reduced bacterial loads and a decreased inflammatory responses in vivo. Together, our results suggest that PPK1 is vital for A. baumannii pathogenicity and persistence.

Polyphosphate Kinase 2 (PPK2) Enzymes: Structure, Function, and Roles in Bacterial Physiology and Virulence

Inorganic polyphosphate (polyP) has been implicated in an astonishing array of biological functions, ranging from phosphorus storage to molecular chaperone activity to bacterial virulence. In bacteria, polyP is synthesized by polyphosphate kinase (PPK) enzymes, which are broadly subdivided into two families: PPK1 and PPK2. While both enzyme families are capable of catalyzing polyP synthesis, PPK1s preferentially synthesize polyP from nucleoside triphosphates, and PPK2s preferentially consume polyP to phosphorylate nucleoside mono- or diphosphates. Importantly, many pathogenic bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii encode at least one of each PPK1 and PPK2, suggesting these enzymes may be attractive targets for antibacterial drugs. Although the majority of bacterial polyP studies to date have focused on PPK1s, PPK2 enzymes have also begun to emerge as important regulators of bacterial physiology and downstream virulence. In this review, we specifically examine the contributions of PPK2s to bacterial polyP homeostasis. Beginning with a survey of the structures and functions of biochemically characterized PPK2s, we summarize the roles of PPK2s in the bacterial cell, with a particular emphasis on virulence phenotypes. Furthermore, we outline recent progress on developing drugs that inhibit PPK2 enzymes and discuss this strategy as a novel means of combatting bacterial infections.