| Topic | Key finding | Organism/system | Year | Source URL | Notes/quantitative data | Citation ID |
|---|---|---|---|---|---|---|
| Identity mapping | The target gene **ppk = PP_5217** in *Pseudomonas putida* KT2440 encodes the main **polyphosphate kinase (PPK1)** corresponding to UniProt **Q88CG4**; the encoded protein is reported as 727 aa and ~34% identical to *E. coli* Ppk. | *Pseudomonas putida* KT2440 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | Deleting **ppk** caused a **70–90% decrease** in intracellular polyP, experimentally validating PP_5217 as the principal polyP-synthesizing enzyme; distinct from **PPK2**, which preferentially uses polyP to regenerate NTPs, especially GTP. | (pqac-00000000, pqac-00000001, pqac-00000013) |
| Enzymatic reaction and core role | PPK1 catalyzes reversible transfer of the terminal phosphate of ATP/NTP to a growing polyphosphate chain: effectively **ATP + polyP(n) → ADP + polyP(n+1)**, with the reaction reversible in principle. | Bacteria; directly relevant to *P. putida* PPK1 | 2013, 2024 | https://doi.org/10.1186/1475-2859-12-50; https://doi.org/10.3390/biom14080937 | PPK1 is the primary polymerase for cytoplasmic polyP formation; polyP functions as a phosphate/energy reserve, ATP buffer, and stress-protective polymer. Recent summaries note bacterial PPK1 is cytoplasmic and works with PPX in polyP homeostasis. | (pqac-00000001, pqac-00000020) |
| Domain/family-based functional inference | PPK1 proteins are large polyP polymerases with strong ATP preference for synthesis and a mechanism involving an autophosphorylated conserved histidine; PPK1 generally favors synthesis over reverse reaction. | Bacterial PPK1 family | 2023 | N/A | Review-level synthesis reports PPK1 as ~75 kDa, four-domain, Mg2+-dependent, highly processive, and typically producing long chains; useful functional inference for Q88CG4 when direct biochemical data for the *P. putida* enzyme are limited. | (pqac-00000018) |
| Cellular localization / pathway context | PPK1 operates in the **cytoplasm**, where it collaborates functionally with PPX and other polyP-utilizing enzymes to maintain intracellular polyP pools. | Bacteria; applicable to *P. putida* | 2024 | https://doi.org/10.3390/biom14080937 | In *P. putida*, **ppk (PP_5217)** and **ppx (PP_5216)** are convergent/overlapping rather than arranged in the classic bicistronic operon seen in enterobacteria, implying different transcriptional control. | (pqac-00000020, pqac-00000013) |
| P. putida mutant phenotype: polyP pool | **Δppk** causes a strong low-polyP phenotype in *P. putida* KT2440. | *P. putida* KT2440 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | PolyP decreased by **~70–90%** across tested conditions; Δppk retained only a minor residual pool (~15–20%), implying limited Ppk-independent polyP synthesis. | (pqac-00000000, pqac-00000005, pqac-00000007) |
| P. putida mutant phenotype: motility and biofilm | Loss of **ppk** reduces swimming motility and impairs biofilm/surface colonization. | *P. putida* KT2440 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | Described as “very limited flagellar activity” and significantly poorer abiotic-surface colonization, consistent with reduced access to high-energy phosphate. | (pqac-00000008, pqac-00000029) |
| P. putida mutant phenotype: stress tolerance | **Δppk** is more sensitive to multiple stresses, including UV, β-lactam antibiotics, heavy metals, solvent stress, and heat. | *P. putida* KT2440 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | Reported stressors include **Cd2+**, **Cu2+**, toluene/solvents, heat shock, and β-lactams; some growth-inhibition differences were significant at **P < 0.05**. | (pqac-00000004, pqac-00000008, pqac-00000009, pqac-00000029) |
| P. putida mutant phenotype: stationary phase and regulation | **Δppk** lowers survival in stationary phase and decreases **rpoS** expression. | *P. putida* KT2440 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | Stationary-phase cultures showed more PI-positive cells and lower viable counts; **PrpoS** activity fell by about **40–50%** in Δppk. | (pqac-00000009, pqac-00000011, pqac-00000012) |
| P. putida mutant phenotype: catalytic vigor / biodegradation | **Δppk** reduces catalytic performance during oxidative biotransformation/biodegradation. | *P. putida* KT2440 carrying TOL plasmid pWW0 | 2013 | https://doi.org/10.1186/1475-2859-12-50 | Growth/catalytic vigor on **m-xylene** dropped to about **50% of wild type** and the mutant showed a longer lag phase; complementation with **ppk** restored the phenotype. | (pqac-00000004, pqac-00000006, pqac-00000011) |
| Industrial-scale transcriptional response | Under repeated glucose limitation / industrial-like mixing stress, **ppk** and related polyphosphate kinase genes are significantly upregulated as part of a rapid energy-buffering response. | *P. putida* KT2440 in STR-PFR scale-down system | 2020 | https://doi.org/10.1111/1751-7915.13571 | Interpreted as a stringent-response–like program supporting ATP homeostasis; context includes rapid starvation pulses, **128 s** PFR exit timepoint, and 3-HA/PHA-derived buffering with ~**1.1% biomass** as 3-HA. | (pqac-00000010) |
| Latest development: starvation/LPS remodeling | PPK controls starvation-linked outer membrane remodeling by enabling lipid A modifications required for polymyxin resistance. | *Escherichia coli* | 2024 | https://doi.org/10.1371/journal.pbio.3002558 | Label-free proteomics identified **92 significantly differentially expressed proteins** between WT and Δppk; Arn/EptA-dependent **L-Ara4N** and **pEtN** lipid A modifications were lost in Δppk. | (pqac-00000015, pqac-00000025) |
| Latest development: metabolic/pathogenesis links and inhibitor discovery | PPK1 was linked to metabolic rewiring and virulence, and compound screening yielded small-molecule inhibitors. | *Mycobacterium tuberculosis* | 2024 | https://doi.org/10.1073/pnas.2309664121 | Screen of **1,280 compounds** found **60** inhibiting PPK-1 activity by **≥50% at 100 µM**; prioritized compounds reduced intracellular polyP by **~35–65%**. | (pqac-00000019) |
| Latest development: anti-virulence inhibitor in vivo | **Scutellarein** was identified as a PPK1 inhibitor that reduced virulence-associated traits and improved infection outcomes. | *Acinetobacter baumannii* | 2024 | https://doi.org/10.1186/s12934-024-02540-9 | In *Galleria mellonella*, treatment at **20 mg/kg** improved survival by about **35%**; assays also used **32–64 µg/mL** in vitro. | (pqac-00000024) |
| Application: phosphorus-removal biotechnology | PolyP metabolism genes including **ppk/ppx** are informative markers of phosphorus-removal performance and stress responses in wastewater systems. | Activated sludge / EBPR-like systems | 2024 | https://doi.org/10.3389/fmicb.2024.1424938 | Chronic Fe(III) exposure over **155 days** shifted metabolism away from Poly-P-centered phosphorus cycling; intracellular P storage fell to **3.11–7.67 mg/g VSS** (**26.01–64.13%** of control). | (pqac-00000026) |
| Application: broader functional annotation relevance | The *P. putida* PPK1/polyP system is best interpreted as an energy/phosphate buffering module that supports stress endurance and industrial robustness rather than an essential central metabolic enzyme. | *P. putida* KT2440 and comparative bacterial systems | 2013–2024 | https://doi.org/10.1186/1475-2859-12-50; https://doi.org/10.1111/1751-7915.13571 | Expert interpretation from the *P. putida* literature emphasizes moderate but reproducible stress and performance phenotypes, supporting annotation as a cytoplasmic PPK1 in polyP homeostasis, starvation adaptation, and stress-linked fitness. | (pqac-00000011, pqac-00000010, pqac-00000017) |


*Table: This table compiles the accession-specific identity, core biochemistry, organism-specific phenotypes, and recent translational developments relevant to Pseudomonas putida KT2440 ppk/PP_5217 (UniProt Q88CG4). It is useful as a compact evidence map for functional annotation and recent literature context.*