Pseudomonas aeruginosa

Ni-Dependent Glyoxalase I (Ni-GloI)#

Detoxifies methylglyoxal, a toxic byproduct of glycolysis that accumulates during rapid growth and metabolic stress.^{[1]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 1 ↓}

The prokaryotic GloI in P. aeruginosa is nickel (Ni)-dependent (unlike the zinc (Zn)-dependent mammalian form), making it a potential drug target with selectivity over the host enzyme.

Also found in other pathogens (N. meningitidis, Y. pestis, Clostridia), but P. aeruginosa is a key model.

Ni-Acireductone Dioxygenase (ARD)#

Part of the methionine salvage pathway. The nickel (Ni)-bound form produces different products than the iron (Fe)-bound form, giving P. aeruginosa metabolic flexibility depending on metal availability. Found across all pathogenic gamma-proteobacteriaceae.

Fe-Dependent Virulence#

Iron is essential for growth and virulence gene expression. Multiple iron-regulated virulence factors: elastase, exotoxin A, alkaline protease. Pyoverdine itself acts as a signaling molecule: iron (Fe)-pyoverdine binding triggers a signaling cascade (FpvA/FpvR/PvdS) that activates virulence gene expression.

Pyoverdine (PVD)—Primary Siderophore#

High-affinity iron chelator, but also binds aluminum(III) (Al3+), cobalt(II) (Co2+), copper(II) (Cu2+), Eu3+, nickel(II) (Ni2+), lead(II) (Pb2+), Tb3+, and zinc(II) (Zn2+) extracellularly.^{[2]Presence of the siderophores pyoverdine and pyochelin in the extracellular medium reduces toxic metal accumulation in Pseudomonas aeruginosa and increases bacterial metal toleranceBraud A, Geoffroy V, Hoegy F et al. · 2010Open reference 2 ↓} Only iron is efficiently imported via the TonB-dependent FpvA pathway; other metals are chelated outside the cell but not taken up.

This extracellular sequestration reduces intracellular accumulation of toxic metals—a defensive strategy.

copper(II) and nickel(II) specifically induce PVD production (290% and 380% increase respectively at 10 uM), suggesting PVD production is a direct response to nickel/copper stress.

Pyochelin (PCH)—Secondary Siderophore#

Chelates aluminum(III) (Al3+), cobalt(II) (Co2+), copper(II) (Cu2+), nickel(II) (Ni2+), lead(II) (Pb2+), and zinc(II) (Zn2+) in addition to iron. PCH is more efficient than PVD at reducing intracellular accumulation of cobalt(II), iron(III) (Fe3+), nickel(II), and zinc(II). Imported via the FptA receptor (iron-loaded only).

Pseudopaline Metallophore#

Nicotianamine-like metallophore analogous to staphylopine in Staphylococcus aureus.^{[1]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 1 ↓} Primary mechanism for nickel acquisition in chelating (metal-restricted) environments. Exported and reimported as metal-pseudopaline complexes via the CntI/CntO system.

Nutritional Immunity Evasion#

The dual siderophore system gives P. aeruginosa a two-pronged strategy: acquire iron for growth while simultaneously detoxifying host-deployed metal poisons. Host calprotectin restricts zinc (Zn) and manganese (Mn) at infection sites; pseudopaline counteracts this.

In the CF lung, chronic iron limitation drives PVD/PCH production, which in turn activates virulence gene expression—creating a positive feedback loop between metal scarcity and pathogenicity.

Connection to Environmental Metal Exposure#

P. aeruginosa is ubiquitous in soil, water, and hospital environments where metal contamination is common. Its siderophore-based metal tolerance system means environmental metal pollution selects for more virulent strains (higher PVD/PCH production = more virulence gene activation).

Nickel-contaminated water sources may promote P. aeruginosa populations with enhanced metal tolerance and virulence capacity.