Juan Imperial

Molybdenum Metabolism and Nitrogen Fixation

Molybdenum is an essential element for nitrogen fixation. No nitrogen fixation can occur in its absence in Klebsiella pneumoniae and no other metal can replace it. However, this is difficult to prove under normal experimental conditions due to the high affinity of nitrogen-fixing cells for molybdenum. Traces present in media or glassware are usually enough to support nitrogen fixation. We devised a method to remove these traces from the medium taking advantage of the high affinity Mo-binding protein of Azotobacter vinelandii. The addition of 10 nM MoO42− to A. vinelandii- treated medium is sufficient for maximum nitrogenase activity in K. pneumoniae. Other sources of Mo, either Mo(VI), Mo(V), or Mo(IV), are also efficiently utilized. In particular, MoS2, the insoluble major natural reservoir, could satisfy the requirements for both Mo and S.