Zinc toxicity and ATP production in Pseudomonas fluorescens.

AIMS

To identify the molecular networks in Pseudomonas fluorescens that convey resistance to toxic concentrations of Zn, a common pollutant and hazard to biological systems.

METHODS AND RESULTS

Pseudomonas fluorescens strain ATCC 13525 was cultured in growth medium with millimolar concentrations of Zn. Enzymatic activities and metabolite levels were monitored with the aid of in-gel activity assays and high-performance liquid chromatography, respectively. As oxidative phosphorylation was rendered ineffective, the assimilation of citric acid mediated sequentially by citrate lyase (CL), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) appeared to play a key role in ATP synthesis via substrate-level phosphorylation (SLP). Enzymes generating the antioxidant, reduced nicotinamide adenine dinucleotide phosphate (NADPH) were enhanced, while metabolic modules mediating the formation of the pro-oxidant, reduced nicotinamide adenine dinucleotide (NADH) were downregulated.

CONCLUSIONS

Pseudomonas fluorescens reengineers its metabolic networks to generate ATP via SLP, a stratagem that allows the microbe to compensate for an ineffective electron transport chain provoked by excess Zn.

SIGNIFICANCE AND IMPACT OF THE STUDY

The molecular insights described here are critical in devising strategies to bioremediate Zn-polluted environments.