Bacteria can express nitrogenase that can fix atmospheric N 2 but they won't work with the critical cereal crops unless the bacteria can interact with roots in the "rhizosphere", the layers of dirt in...Bacteria can express nitrogenase that can fix atmospheric N 2 but they won't work with the critical cereal crops unless the bacteria can interact with roots in the "rhizosphere", the layers of dirt intimately in contact with roots.