Nitrogen fixing ability of rhizobium is significant for the growth of grass family. The stronger of its ability, the less chemical fertilizer will be used. Molybdenum is a key integral part of nitrogen fixing enzyme in rhizobium and Mo is also important for the growth of plants themselves. However, Mo is heavy mental. The abuse of it will cause environment pollution. Hence, spot application of Mo is of great importance. A plasmid was transfer into E.coli Promethus to make it express fusion protein, one side of which anchors on the out membrane and the other side of which,ModA,catches molybdate. With the help of organic acid tendency system, our Promethus will head for the roots. A suicide system depending on time is also design for the reason of bio-safety. E.coli Promethus will deliver Mo directly to the root of plants. This will also open a new chapter of biological fertilizer.