452 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



areas. The organisms responsible for nitrogen fixation in these non- 

 leguminous plants have not been definitely identified but they are 

 believed to be Actinomycetes. 



An interesting association has been found recently between a nitro- 

 gen-fixing bacterium occurring in "leaf nodules" of a subtropical plant 

 Psychotria hacteriophila. The bacterium, identified as a Klebsiella^ 

 is the first example of a symbiotic microorganism that will fix nitrogen 

 when grown in the absence of its host. Another interesting feature is 

 that this bacterium not only fixes nitrogen gas but is also involved in 

 the synthesis of substances that promote growth in the host plant and 

 are essential for its normal development. 



Not all the examples given in table 1 have been thoroughly checked 

 for their fixation abilities and it is still doubtful whether the yeast 

 Rhodotorula is able to fix gaseous nitrogen. Claims have been put 

 forward for other microorganisms either alone or in association with 

 other organisms such as actinomycetes, yeasts, mycorhiza, and lichens, 

 and for some unusual associations of bacteria with insects and goats. 

 These reports of nitrogen fixation, however, have still to be confirmed. 



Atmospheric nitrogen is relatively inert. The industrial synthesis 

 of ammonia from nitrogen and hydrogen requires temperatures of 

 about 500° C. and pressures above 350 atmospheres. The process con- 

 sumes a great deal of energy — equivalent to 5 tons of coal per ton of 

 nitrogen (see table 2). By contrast, microbial fixation works at 

 ordinary temperatures and pressures. 



Although the assimilation of carbon dioxide in photosynthesis in 

 green plants has been resolved, largely through the brilliant work of 

 Calvin and his associates at Berkeley, the equally important mecha- 

 nism of nitrogen fixation is still relatively unexplored. Since the 

 pioneer work carried out over 20 years ago by Virtanen and his col- 

 leagues in Helsinki, and by Burris and Wilson and their group at 

 the University of Wisconsin, progress has, until recently, been slow. 

 There were two main reasons. The first was the lack of success in 

 extracting the nitrogen-fixing enzymes from living cells, and the sec- 

 ond has been the absence of satisfactory isotopes of nitrogen for 

 "tracer" studies of the fate of nitrogen gas in the bacteria. Only 



Table 2. — Materials and energy requirements for the industrial production of 

 ammonia from nitrogen and hydrogen (1 ton liquefied ammonia) 



Natural gas (92 percent CH4) 26,000 cu. ft. 



Catalyst for shift reaction 0.3 lb. 



Synthesis catalyst 0.5 lb. 



Caustic soda 8 lb. 



Monethanolamine 0.3 lb. 



Fuel gas 22,000,000 B.t.u. 



Electricity 108kw-hr. 



Water 6,000 gal. 



