Molybdate transporter ModABC is important for Pseudomonas aeruginosa chronic lung infection.

Simone Périnet,Julie Jeukens,Myriam M Ouellet,Steve J Charette,Irena Kukavica-Ibrulj,Roger C Levesque

doi:10.1186/s13104-016-1840-x

Abstract

BackgroundMechanisms underlying the success of Pseudomonas aeruginosa in chronic lung infection among cystic fibrosis (CF) patients are poorly defined. The modA gene was previously linked to in vivo competitiveness of P. aeruginosa by a genetic screening in the rat lung. This gene encodes a subunit of transporter ModABC, which is responsible for extracellular uptake of molybdate. This compound is essential for molybdoenzymes, including nitrate reductases. Since anaerobic growth conditions are known to occur during CF chronic lung infection, inactivation of a molybdate transporter could inhibit proliferation through the inactivation of denitrification enzymes. Hence, we performed phenotypic characterization of a modA mutant strain obtained by signature-tagged mutagenesis (STM_modA) and assessed its virulence in vivo with two host models.ResultsThe STM_modA mutant was in fact defective for anaerobic growth and unable to use nitrates in the growth medium for anaerobic respiration. Bacterial growth and nitrate usage were restored when the medium was supplemented with molybdate. Most significantly, the mutant strain showed reduced virulence compared to wild-type strain PAO1 according to a competitive index in the rat model of chronic lung infection and a predation assay with Dictyostelium discoideum amoebae. As the latter took place in aerobic conditions, the in vivo impact of the mutation in modA appears to extend beyond its effect on anaerobic growth.ConclusionsThese results support the modABC-encoded transporter as important for the pathogenesis of P. aeruginosa, and suggest that enzymatic machinery implicated in anaerobic growth during chronic lung infection in CF merits further investigation as a potential target for therapeutic intervention.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-016-1840-x) contains supplementary material, which is available to authorized users.

Highlights

Mechanisms underlying the success of Pseudomonas aeruginosa in chronic lung infection among cystic fibrosis (CF) patients are poorly defined
In the 6.3 Mbp genome of P. aeruginosa strain PAO1, modA (PA1863) is encoded in a putative operon with modB (PA1862) and modC (PA1861) (Fig. 1). Their products correspond to the 26.4 kDa (252 AA) molybdate-binding periplasmic protein precursor ModA, molybdenum membrane transport protein ModB (24.4 kDa) and ATPase ModC (39.8 kDa). These annotations are based on AA identity with ModABC from E.coli [31], where the modABC transcription unit codes for an ATP-binding cassette (ABC) transporter of molybdate, and were confirmed by Pederick and colleagues [18] using a modA deletion mutant
Wild-type modABC was provided in trans to the mutant strain for complementation analysis using the expression vector pUCP19

Summary

Introduction

Mechanisms underlying the success of Pseudomonas aeruginosa in chronic lung infection among cystic fibrosis (CF) patients are poorly defined. The modA gene was previously linked to in vivo competitiveness of P. aeruginosa by a genetic screening in the rat lung This gene encodes a subunit of transporter ModABC, which is responsible for extracellular uptake of molybdate. This compound is essential for molybdoenzymes, including nitrate reductases. Since anaerobic growth conditions are known to occur during CF chronic lung infection, inactivation of a molybdate transporter could inhibit proliferation through the inactivation of denitrification enzymes. Mo is incorporated into the molybdenum cofactor (MoCo) and was found to be essential for the activity of molybdoenzymes These enzymes catalyze various oxidation/reduction reactions and are implicated in the metabolism of nitrogen, carbon and sulfur. All nitrate reductases required for P. aeruginosa anaerobic growth require a MoCo cofactor [11], which can contain either Mo or tungsten (W) [14]

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Conclusion