Ferredoxins are small electron carrier proteins that participate in various redox reactions. FdVI is an essential protein required for growth of R.capsulatus. May be involved in Fe-S cluster assembly. Binds 1 [2Fe-2S] cluster. Seems to be constitutively expressed. Is expressed at a similar level under N-limited and N-sufficient conditions. Disruption of this gene is lethal. Belongs to the adrenodoxin/putidaredoxin family.