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Abstract
It was reported recently (Oomen and Corden, 1970) that a group of natives of highland New Guinea were leading active and healthy lives while consuming much less than the minimum daily requirement (MDR) for protein nitrogen (approximately 4g/day, whereas the MDR is around 10g/day [Oemen, 1970]) On the basis of detailed nutritional analyses, Oomen made the radical suggestion that the key to this anomaly lay in a unique adaptation of the intestinal flora; atmospheric nitrogen could be fixed by the bacterial population and nitrogenous products absorbed as nutrients to supplement the nitrogen-deficient diet (Oomen, 1970) Following this suggestion, Bergersen and Hlpsley (1970) reported isolating nitrogen-fixing bacteria, predominantly strains of Klebsiella pneumoniae. "at high titers" from the feces of the New Guineans At a time when many sincere individuals the world over are working in an atmosphere of permanent crisis to solve the world food problem, one might expect that these studies would stimulate a major effort to substantiate and explain the unusual findings However, no further attempt to either prove or disprove Oomen's radical proposal has been reported.
Fixation of atmospheric nitrogen ranks with photosynthesis as one of the most important processes in the economies of both nature and man By fixation the inert dlnitrogen molecule is split and reduced to two molecules of the more reactive ammonia which is capable of undergoing the complex transformations of nitrogen metabolism Although it is difficult to measure accurately on a global scale, biological fixation provides on the order of 2/3 of all fixed nitrogen (Hardy and Havelka, 1975) This enzymatic fixation is carried on by a variety of free-living and symbiotic bacteria There are no known eukaryotic organisms capable of fixing nitrogen The biochemistry of nitrogen fixation has been subjected to extensive study and many details of the process are known (Hardy and Burns 1968; Streicher and Valentine 1973) The genetics and molecular biology of the nitrogen-fixing enzyme complex have also received much attention especially with the hope of transferring the nitrogen fixation genes to higher organisms (Shanmugam and Valentine 1975). A potentially more important development however may be improved symbiotic relationships (Marx 1974).
Fixation in plant symbionts has received the majority of attention since this is a key point at which man may hope to improve agricultural yields However several nitrogen-fixing animal symbionts are known: in termites they seem to be capable of supplying the entire nitrogen needs of whole colonies (Benemann, 1973; Breznak et al. 1973); in ruminants nitrogen-fixing bacteria have been isolated by a number of workers (Postgate, 1970; Elleway et al. 1971; Granhall and Ciszuk, 1971); and finally in man (Bergersen and Hipsley 1970) The suggestion has been made that the possibly unique symbiosis apparently existing in the intestines of the New Guineans might serve as a model for "solving the protein supply problem directly" (Benemann and Valentine 1972), However* again, there have been no reported efforts to further investigate this intriguing possibility.
The object of the present study was to explore the prevalence of these bacteria In human feces by attempting to titer, isolate, and identify nitrogen-fixing bacteria from readily available stool samples. Preliminary tests indicated that a variety of organisms isolated from human feces are able to grow on nitrogen-free media However, sufficient quantities of fixed nitrogen can occur as contaminants in the gaseous, liquid or solid components of the culture's environment to allow slow growth to take place Therefore, since the conversion of acetylene to ethylene is a specific property of the nitrogen fixation system, the very sensitive acetylene reduction assay was applied to verify nitrogen fixing ability and to estimate rates of nitrogen fixation The results obtained and a variety of theoretical considerations suggest that Oomen's hypothesis may be correct.
