Evidence for the occurrence of the alternative, vanadium-containing nitrogenase in the cyanobacterium<i>Anabaena variabilis</i>

Abstract

Anabaena variabilis can be grown with dependence on either molybdenum (Mo) or vanadium (V) in the medium with essentially the same growth rates. Vanadium cultures reduce C2H2 to C2H4 and partly (to 2–3%) to C2H6. These C2H4 and C2H6 formations can be shown to be strictly light dependent, proving that the gases are formed by the cyanobacterium. C2H4 and C2H6 productions are accompanied by a H2 formation which is much higher than in Mo cultures. Maximal C2H2-formation rates are 2/3 lower in V-grown cells compared to Mo control cultures. This is the first demonstration of a light-dependent ethane formation and of the occurrence of the alternative nitrogenase in any phototroph.