| Category | Key points | Best supporting sources (with year and DOI/URL where available) |
|---|---|---|
| Identity | **Target verified:** UniProt **Q88GC8** in *Pseudomonas putida* KT2440 corresponds to **pvdA / PP_3796**, an **L-ornithine N5-monooxygenase (ornithine hydroxylase)** in pyoverdine biosynthesis; this matches the UniProt description and the broader Pseudomonas pyoverdine literature. *P. putida* studies treat **pvdA** as a pyoverdine structural gene, while foundational biochemical characterization is mainly from the close homolog in *P. aeruginosa*. (pqac-00000008, pqac-00000010) | Barrientos-Moreno et al., **2019**, *J Bacteriol*; DOI: https://doi.org/10.1128/jb.00454-19. Rice, **2010** (primary characterization thesis/article excerpt). |
| Reaction | **Primary function:** catalyzes **N5-hydroxylation of L-ornithine** to make **N5-hydroxyornithine**, which is then **formylated by PvdF** to produce **L-fOHOrn** for incorporation into the pyoverdine peptide backbone. This is an early, committed tailoring step in pyoverdine assembly. (pqac-00000001, pqac-00000004, pqac-00000008) | Dell’Anno et al., **2022**, DOI: https://doi.org/10.3390/ijms231911507. Schalk, **2025**, DOI: https://doi.org/10.1038/s41579-024-01090-6. |
| Cofactors & mechanism | PvdA belongs to the **flavin-dependent N-hydroxylating monooxygenase / Class B FMO** family. Mechanistic evidence from *Pseudomonas* and related homologs indicates use of **FAD**, **molecular oxygen**, and typically **NADPH** as reductant; catalysis proceeds through a **C4a-hydroperoxyflavin** intermediate. Purified bacterial NMOs can require **exogenous FAD** because recombinant proteins may be partially flavin-deficient. A kinetic study cited in recent reviews reports that in PvdA, **substrate binding triggers O2 addition but not flavin reduction**. (pqac-00000003, pqac-00000006, pqac-00000009, pqac-00000011) | Chocklett, **2009** (mechanistic NMO background). Rice, **2010** (PvdA characterization excerpt). Schalk, **2025**, DOI: https://doi.org/10.1038/s41579-024-01090-6. |
| Pathway role | PvdA functions in the **cytoplasmic phase** of **pyoverdine siderophore biosynthesis**, supplying a modified amino acid building block needed by the **NRPS assembly line**. Pyoverdine is the major/specific siderophore used by fluorescent pseudomonads for **high-affinity Fe(III) acquisition**; the mature siderophore has extremely high ferric affinity (~**10^-32 M^-1** reported in the pathway literature). (pqac-00000002, pqac-00000004, pqac-00000005, pqac-00000007, pqac-00000016) | Dell’Anno et al., **2022**, DOI: https://doi.org/10.3390/ijms231911507. Manko et al., **2024**, DOI: https://doi.org/10.3390/ijms25116013. Stein et al., **2023**, DOI: https://doi.org/10.1128/spectrum.02300-23. |
| Cellular localization & complex context | Pyoverdine biosynthesis starts in the **cytoplasm**, with later **periplasmic maturation** and secretion. Recent cell-biological studies in *P. aeruginosa* indicate that PvdA can **physically interact with all four pyoverdine NRPSs** and is part of a **membrane-associated multienzyme “siderosome” context**; Schalk’s review also notes an **N-terminal hydrophobic inner-membrane-anchoring region** and varying interaction stoichiometries with NRPS partners. Direct isolation of the full complex remains incomplete. (pqac-00000001, pqac-00000002, pqac-00000004) | Manko et al., **2024**, DOI: https://doi.org/10.3390/ijms25116013. Dell’Anno et al., **2022**, DOI: https://doi.org/10.3390/ijms231911507. Schalk, **2025**, DOI: https://doi.org/10.1038/s41579-024-01090-6. |
| Regulation & conditions | pvdA is embedded in the canonical **iron-starvation-responsive pyoverdine regulon**, typically controlled by **Fur** and pyoverdine sigma-factor circuitry in pseudomonads. In *P. putida* KT2440, **arginine biosynthesis defects** alter pyoverdine gene expression: **pvdA** and **pvdD** increase, but **pvdE** decreases, consistent with impaired maturation/export rather than simple biosynthetic shutdown. Recent 2024 work in *P. aeruginosa* identified **BfmRS** as a direct regulator of siderophore genes under **osmotic stress**; homologous BfmR from *P. putida* KT2440 could bind promoters of key siderophore genes, suggesting conservation of this regulatory logic across pseudomonads. Also, **parXY** expression is iron responsive: **10 µM FeCl3** reduced parXY promoter activity by ~**7-fold**, whereas **1 mM bipyridyl** increased it ~**2-fold**. (pqac-00000008, pqac-00000010, pqac-00000018, pqac-00000021) | Barrientos-Moreno et al., **2019**, DOI: https://doi.org/10.1128/jb.00454-19. Song et al., **2024**, DOI: https://doi.org/10.1038/s42003-024-05995-z. Stein et al., **2023**, DOI: https://doi.org/10.1128/spectrum.02300-23. |
| Phenotypes & quantitative data | In *P. putida* KT2440, pyoverdine homeostasis is tightly linked to secretion and stress adaptation. **ΔargG/ΔargH** mutants show **higher pvdA/pvdD expression** but **reduced extracellular pyoverdine** with **intracellular retention**, and **higher ROS** by CellROX assays; figure-based evidence shows increased intracellular vs extracellular pyoverdine and reduced **pvdE** expression. For secretion, Stein et al. found that in a **ΔpvdRT-opmQ ΔmdtA** background (**Δpm**), adding **ΔparX** caused the strongest extra defect under iron limitation: **AUC ~40% of Δpm**, while a pyoverdine-nonproducer was ~**2% of Δpm**. **1 µM FeCl3** rescued the triple-mutant growth defect to Δpm levels, and **10 µM pyoverdine** gave the best rescue; **1 µM CuSO4** did not. parX deletion also caused ~**2-fold** lower **mdtABC-opmB** and **pvdL** expression in reporter assays. (pqac-00000010, pqac-00000012, pqac-00000017, pqac-00000018, pqac-00000021) | Barrientos-Moreno et al., **2019**, DOI: https://doi.org/10.1128/jb.00454-19. Stein et al., **2023**, DOI: https://doi.org/10.1128/spectrum.02300-23. |
| Recent developments & applications | **2023–2024** work has shifted from simple gene-function assignment to **pathway organization and export control**: (i) **ParXY** was added to the network of overlapping pyoverdine secretion systems in *P. putida* KT2440; (ii) **PvdL/NRPS spatial organization** and PvdA interactions were visualized in live cells; (iii) **BfmRS** linked environmental stress to siderophore regulation. Reviews emphasize broader applications of pyoverdine biology in **biotechnology, synthetic biology, antimicrobial targeting, and environmental metal acquisition**, making PvdA relevant both as a **biosynthetic engineering node** and as a potential **anti-virulence target** by blocking siderophore production. (pqac-00000000, pqac-00000002, pqac-00000016) | Stein et al., **2023**, DOI: https://doi.org/10.1128/spectrum.02300-23. Manko et al., **2024**, DOI: https://doi.org/10.3390/ijms25116013. Dell’Anno et al., **2022**, DOI: https://doi.org/10.3390/ijms231911507. Schalk, **2025**, DOI: https://doi.org/10.1038/s41579-024-01090-6. |


*Table: This table summarizes the best-supported functional annotation for *Pseudomonas putida* KT2440 pvdA (UniProt Q88GC8), integrating organism-specific evidence with mechanistic data from closely characterized homologs. It highlights reaction chemistry, pathway role, localization, regulation, phenotypes, and recent 2023–2024 developments.*