MrdH, a Novel Metal Resistance Determinant of Pseudomonas putida KT2440, Is Flanked by Metal-Inducible Mobile Genetic Elements

A. Haritha (1) , P. Sagar (1) , A. Tiwari (1) , P. Kiranmayi (1) , Agnès Rodrigue (2) , P. M. Mohan (1) , S. S. Singh (1)

1 Osmania University
2 MAP - Microbiologie, adaptation et pathogénie

We report here the identification and characterization of mrdH, a novel chromosomal metal resistance determinant , located in the genomic island 55 of Pseudomonas putida KT2440. It encodes for MrdH, a predicted protein of 40 kDa with a chimeric domain organization derived from the RcnA and RND (for resistance-nodulation-cell division) metal efflux proteins. The metal resistance function of mrdH was identified by the ability to confer nickel resistance upon its complementation into rcnA mutant (a nickel-and cobalt-sensitive mutant) of Escherichia coli. However, the disruption of mrdH in P. putida resulted in an increased sensitivity to cadmium and zinc apart from nickel. Expression studies using quantitative reverse transcription-PCR showed the induction of mrdH by cadmium, nickel, zinc, and cobalt. In association with mrdH, we also identified a conserved hypothetical gene mreA whose encoded protein showed significant homology to NreA and NreA-like proteins. Expression of the mreA gene in rcnA mutant of E. coli enhanced its cadmium and nickel resistance. Transcriptional studies showed that both mrdH and mreA underwent parallel changes in gene expression. The mobile genetic elements Tn4652 and IS1246, flanking mrdH and mreA were found to be induced by cadmium, nickel, and zinc, but not by cobalt. This study is the first report of a single-component metal efflux transporter, mrdH, showing chimeric domain organization, a broad substrate spectrum, and a location amid metal-inducible mobile genetic elements. Bacterial efflux systems for inorganic metal cations and an-ions play an imperative role in the regulatory network governing metal homeostasis. These efflux systems are also important for the environmental adaptability of the bacteria thriving in metal-rich serpentine environments. Bioinformatic and functional genomic analyses have revealed that the efflux systems belonging to the resistance-nodulation-cell division (RND), cation diffusion facilitator (CDF), and P-type ATPases constitute the majority of the multiple layers of heavy metal resistance in an organism (36). Members of the RND protein family include group of bacterial transport proteins involved in heavy metal resistance, nodulation, and cell division. The best-characterized RND family members include the efflux systems CzcCBA (Cd 2 , Zn 2 , and Co 2 resistance), CnrCBA (Co 2 and Ni 2 resistance), and NccCBA (Ni 2 , Co 2 , and Cd 2 resistance) from Cupriavidus metallidurans (Alcaligenes metal-lidurans or Ralstonia metallidurans) and the CznCBA efflux system (Co 2

Domaines: Bactériologie; Génomique, Transcriptomique et Protéomique [q-bio.GN]; Biochimie [q-bio.BM]; Biologie moléculaire

A. Haritha, P. Sagar, A. Tiwari, P. Kiranmayi, Agnès Rodrigue, et al.. MrdH, a Novel Metal Resistance Determinant of Pseudomonas putida KT2440, Is Flanked by Metal-Inducible Mobile Genetic Elements. Journal of Bacteriology, 2009, 191 (19), pp.5976 - 5987. ⟨10.1128/JB.00465-09⟩. ⟨hal-01667581⟩