Isolation of self sustaining nitrogen fixing bacteria from soil

Abstract

Nitrogen fixation is energetically an expensive process and therefore the nitrogen-fixing microorganisms which are collectively called diazotrophs must acquire sufficient energy for nitrogen-fixation process to go on. There are reports that free-living nitrogen-fixing bacteria derive energy from breakdown of cellulose by cellulolytic heterotrophs. In this connection, widespread cooperation between Azotobacter spp. and some cellulolytic bacteria like Cellulomonas spp. and Bacillus spp. have been reported. Such cooperative nitrogen-fixation has also been reported between Azospirillum spp. and Cellulomonas spp. and Bacillus spp. This cooperative process not only has great ecological significance but is also important from agricultural point of view. The cellulolytic flora need nitrogen to carry out cellulose breakdown and therefore cause depletion of available soil nitrogen if it is not continuously replenished by nitrogen-fixing flora. Such depletion of soil nitrogen then affects further breakdown of cellulose materials. In the cooperative process in which both cellulolytic microflora and free-living nitrogen-fixing microflora coexist, the process of cellulose breakdown continues without further depletion of nitrogen as both types are benefited by this process. But there is a disadvantage in this process in that, the cooperative process is restricted by various environmental factors which may not be suitable for two types of organisms to work under the same sets of conditions. Further, the cooperative process is uneconomic as the limited energy is shared by both types of organisms and as a result neither the energy produced nor the nitrogen fixed in the process is saved for other microorganisms. The nitrogen share of plant also remains limited. Contrary to the above cooperative process, an interesting phenomenon has been reported in 1983 which however has not been given due importance it actually deserved. This is related to peculiar ability of certain free-living nitrogen-fixing bacteria to sustain themselves by...