K. pneumoniae is closely related to the non-nitrogen fixing bacterium E. coli. Similar genetic analysis can be applied to both the organisms and genes could be transferred among them. Nitrogenase activity in E. coli carrying the nif plasmid pRDI was found to be equivalent to that in the parent K. pneumoniae strain under suitable conditions.

Transfer of pRDI to Agrobacterium tumefaciens did not result in nitrogen fixing recombinants. Mutants of Azotobacter Vinelandii lacking either nitrogenase compenent I or II regained these activities when pRDI was transferred to them. Azotobacter sp. are obligate aerobes. A protein which binds to the enzyme complex protects the nitrogenase from oxygen inactivation. It would be of great interest to isolate these genes which encode this protein and to trasfer the oxygen protection to other nitrogen fixing systems and to new hosts together with K. pneumoniae nif genes.

During nitrogen fixation hydrogen is evolved with concomitant ATP hydrolysis. Many nitrogen fixing bacteria have uptake hydrogenases which save energy by recycling hydrogen to water, releasing electrons. It will be advantageous to introduce such uptake hydrogenases along with nif genes into new hosts which do not possess them.

An attempt to get nif gene expression in eukaryotic cells will have to overcome considerable problems. There are basic differences in the organization, transcription and translation of genes in prokaryotes and eukaryotes. Technical difficulties of placing genes into cereals have been overcome but there are other problems to the overcome. The eukaryotic promoters and other control sequences have to be spliced into the operons to ensure expression in plant cells as nif genes are prokaryotic in nature.

If the nif genes get expressed, the plant would have to supply reducing power and 17 moles of ATP per mole of nitrogen fixed, and maintain the nitrogenase in oxygen depleted environment. This may lead to yield loss. However, since plants spend a great deal of energy for extracting nitrate from soil anyway, this energy deficit may not be deleterious to yield. Maize is capable of compensating for this energy loss than Soyabean.

The nif gene cluster from K. pneumoniae has been transferred to Saccharomyces cerevisiae but the expressions of the genes have not been reported.

As the cost of producing artificial fertilizers will probably continue to rise, it is an attractive proposition to produce agronomically desirable cultivars with a partial or total ability to fix atmospheric nitrogen. Such plants could make use of the readily available resource of gaseous nitrogen. Before this can be achieved, considerably more information must be obtained about the molecular mechanism of nitrogen fixation and about the means of transferring nif genes to obtain its expression. The difficulty of these tasks should not be underestimated at this time.

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