HOW DO MICROBES "FIX" NITROGEN FROM THE AIR? — NICHOLAS 459 



Most of the world's agricultural nitrogen is still supplied by soil 

 microorganisms. A grass-clover pasture is capable of fixing over 500 

 pounds of nitrogen per acre in a year. Some interesting and exciting 

 possibilities exist for inducing other types of microorganisms to fix 

 nitrogen and encouraging symbiotic associations with other economic 

 crops. Why should not grasses, cereals, or brassica crops or fruit trees 

 have their own built-in symbiotic associations with nitrogen-fixing 

 microorganisms? The answers to such questions — which could revo- 

 lutionize agriculture and go a long way to producing food supplies 

 cheaply — must await the results of fundamental research work on the 

 basic mechanism and requirements of the fixation process in free-living 

 microorganisms and in those in symbiotic association with plants. The 

 immediate requirement is the separation and purification of the nitro- 

 gen fixing enzymes from cell-free preparations of microorganisms. 

 There is no doubt that the mechanism of activation of nitrogen gas 

 will be resolved eventually with the aid of chemical and physical tech- 

 niques now being developed, but these studies must also seek an un- 

 derstanding of the cell organization and structure. 



How the industrial process for forming ammonia from nitrogen and 

 hydrogen works is still not completely understood, though it was 

 developed at the turn of the century. It provides a relatively simple 

 inorganic model for ammonia production, involving a solid catalyst 

 based on iron oxide supplemented with salts of aluminum and prob- 

 ably those of molybdenum and vanadium, but it is significant that the 

 main clues to the mechanism of nitrogen fixation have come from work 

 with the biological system. It has been suggested in some quarters 

 that by solving the problem of nitrogen fixation by microbial enzymes 

 the process might then be exploited to produce nitrogenous fertilizers 

 cheaply. This view may be too optimistic. There is no doubt, how- 

 ever, that some novel features in catalysis involving iron and possibly 

 molybdenum will be found when the nitrogen-fixing enzyme system 

 is eventually crystallized and analyzed by modem methods. 



