strain CIB [21], the fdx gene belongs to a cluster of genes involved in anaerobic catabolism of aromatic compounds (Figure 2). In Thauera aromatica, Fdx receives electrons from 2-oxoglutarate:Fdx #HKI272 randurls[1|1|,|CHEM1|]# oxidoreductase and donates them to benzoyl-CoA reductase, the ATP-dependent dearomatizing enzyme [17]. By similarity, the fdx gene likely belongs to a catabolic operon [16] in the other anaerobic benzoate-degrading bacteria displaying clustered homologous genes [19, 21]. Figure 2 Genomic context around genes of the AlvinFdx family in selected bacteria. The predicted ORFs neighbouring fdx are approximately drawn to scale (shown at the bottom) with arrows indicating the direction of

transcription. Genes and encoded proteins: P. aeruginosa PAO1: PA0364, probable oxidoreductase; coaD, phosphopantetheine adenylyltransferase; PA0361, probable γ-glutamyltranspeptidase precursor; PA0360, conserved hypothetical protein. E. coli K12-MG1655: yfhH, conserved hypothetical PCI-34051 in vivo protein; acpS, CoA:apo-[acyl-carrier-protein] pantetheinephosphotransferase; pdxJ, pyridoxin 5′-phosphate synthase;

recO, protein that interacts with RecR and possibly RecF proteins. H. pylori 26695: addB, ATP-dependent nuclease; HP0276, hypothetical protein; gppA, guanosine pentaphosphate phosphohydrolase; rfaC, lipopolysaccharide heptosyltransferase-1. T. aromatica: bcrAD, two of the four subunits of benzoyl-CoA reductase; orf1 and orf2, hypothetical proteins. The Figure was prepared with tools available at http://​cmr.​jcvi.​org and with the data in [20]. A case of interest is that of Azoarcus sp. EbN1 (called Aromatoleum aromaticum strain EbN1 in the most recent literature) which anaerobically degrades aromatics and displays a ferredoxin gene (improperly designated by fxd) in the

bcr (benzoyl CoA reductase) genomic cluster [22]. Although it most probably binds two [4Fe-4S] clusters, the “”Fxd”" ferredoxin Montelukast Sodium does not have the sequence characteristics of Fdx (sequence [13] of Figure 1A). Furthermore, in another part of the genome downstream of the pantetheine-phosphate adenylyltransferase gene (coaD), Azoarcus sp. EbN1 does have a fdx gene (locus NT01AE0820, sequence [9] of Figure 1A), potentially encoding a Fdx of the AlvinFdx family. Thus it seems unlikely that the latter Fdx participates in the anaerobic degradation of aromatics in this bacterium. The coaD gene was found on the 5′ side of fdx in several bacteria including P. aeruginosa PAO1. However, the involvement of Fdx in the reaction catalyzed by phosphopantetheine adenylyltransferase has not been demonstrated, and the very high-energy electrons Fdx may provide are not required in the CoA biosynthetic pathway. Thus, coaD and fdx1 do not need to be functionally linked. Furthermore, coaD and fdx1 are not always close in the sequences of many genomes, in E. coli K12-MG1655 for instance (Figure 2), and the layout around fdx is highly variable (Figure 2). In P.