 It is probable that "Natronomonas" uses ferredoxin and not NADH as the electron donor for all three reductive conversions.This is evident from the occurrence of conserved ferredoxin-binding residues within the N. pharaonis NirA protein and ferredoxin dependence of nitrate and nitrite reductases in the halophile "Haloferax mediterranei".Strains of "N. pharaonis" were first isolated from highly saline soda lakes in Egypt and Kenya, which show pH values around 11.