aeruginosa (Figure 3), but little previous work addressed its regulation. The transcriptome subset varying between biofilm and planktonic cultures of P. aeruginosa Milciclib in vivo PAO1 has been reported [29]: fdx1 transcription was increased ca. 3 times in biofilms as compared to free living bacteria. However, such variations were not confirmed in another similar study [30]. Considering other members of the AlvinFdx family, one of the two fdx

genes in Campylobacter jejuni (sequence [14] of Figure 1A) was found to be iron-regulated and involved in the aerobic survival of cells in the stationary phase [31]. The sequence of another Fdx of this bacterium (sequence [7] of Figure 1A) is more similar to the Fdx consensus. We could not demonstrate iron regulation for the single fdx gene of P. aeruginosa or E. coli (not shown), in line with previous results obtained

with H. pylori [32] and P. aeruginosa [33]. H. pylori strains are of particular interest since their only annotated ferredoxin gene is of the type discussed here. The encoded protein has been associated with metronidazole resistance, at least for some strains AZD1480 concentration [34, 35], including because it is suspected to Luminespib clinical trial donate electrons to a nitroreductase (the product of the frxA gene) that is required to activate the drug. The observation that the gene could be deleted in some, but not all, H. pylori strains [35] did not help assigning a function to Fdx. In particular, the actual involvement of Fdx as low potential electron shuttle between oxidoreductases in H. pylori as suggested [34] remains to be clearly delineated since Fdx Meloxicam proteins have been shown to be poor electron donors/acceptors in coupled reactions using such enzymes [36, 37]. Indeed, flavodoxin has been assigned this role in H. pylori and C. jejuni [37]. Furthermore, the induced high-level expression of frxA resulting from the deletion of fdx in some H. pylori strains suggested a repressor function for fdx and additional important, but undefined, roles [35]. The genome context around the fdx genes is not conserved in different bacteria, and evidence for transcription

as part of an operon is lacking, with the exception of clusters of genes involved in the anaerobic degradation of aromatic compounds [19–21]. In P. aeruginosa several, often putative, oxidoreductases can be identified in the analysis of the genome, and many low-potential electron transfer molecules coexist. P. aeruginosa fdx1 is transcribed as a short messenger in a constitutive-like manner, and our attempts at deleting fdx1 indicated that it belongs to the minority of essential genes (estimated around 10% [38]) in this bacterium. This conclusion agrees with the absence of P. aeruginosa transposon mutants for PA0362, both in PAO1 http://​pseudomutant.​pseudomonas.​com/​index.​html and PA14 http://​pga.​mgh.​harvard.​edu/​Parabiosys/​projects/​host-pathogen_​interactions/​library_​construction.​php libraries.