The enzymes of the Wood-Ljungdahl pathway (a) and the corresponding gene cluster (b).

<p>Cluster I: two genes for formate dehydrogenase (<i>fdhF</i>) are organized together with three copies of a FeS-containing subunit of a [FeFe]-hydrogenase (<i>hycB</i>), a formate dehydrogenase accessory protein (<i>fdhD</i>) and another subunit of the [FeFe]-hydrogenase (<i>hydA2</i>). Cluster II: genes for formyl-THF synthetase (<i>fhs1</i>), methenyl-THF cyclohydrolase (<i>fchA</i>), methylene-THF dehydrogenase (<i>folD</i>) and methylene-THF reductase (<i>metF, metV</i>) are organized together with a RnfC-similar protein (<i>rnfC2</i>). Cluster III: genes for the subunits of the CO dehydrogenase/acetyl CoA synthase complex consisting of CO dehydrogenase (<i>acsA</i>), acetyl-CoA synthase (<i>acsB1</i>), corrinoid-iron sulfur protein (<i>acsCD</i>) and methyltransferase (<i>acsE</i>) are organized together with two copies of a CODH nickel-insertion accessory protein (<i>cooC</i>), a corrinoid activation/regeneration protein (<i>acsV</i>) and two hypothetical proteins (Orf1 and Orf2).