THE INFLUENCE OF FIXED NITROGEN ON AZOTOBACTER

Abstract

The nitrogen-fixing organism, Azotobacter, has been little studied with reference to its normal physiological behavior in fixed nitrogen, and especially in comparison with that in free nitrogen. A knowledge of the physiology of Azotobacter growing in readily available fixed nitrogen is highly essential to controlling the interpretation of the physiological behavior of Azotobacter when fixing nitrogen, particularly in connection with ascertaining the nature of the chemical mechanism of nitrogen fixation. In accordance with this logical principle, Burk (1930) has already shown, for example, that the unique oxygen pressure functions of Azotobacter with respect to respiration, growth, nitrogen fixa-tion, efficiency of growth, efficiency of nitrogen fixation, pH, and humic acid are qualitatively identical whether the nitrogen supply is either free or fixed, and hence that these functions do not concern directly the chemical mechanism of fixation. Bonazzi (1924), Zoond (1926), Kostyschew, Ryskaltschuk and Schwezowa (1926), and others have shown that Azotobacter is able to utilize nitrates, ammonium salts, amino acids, and pep-tones, etc., in preference to free nitrogen, and that fixation is, indeed, not an essential function. In establishing the quantitative aspects of these relations, however, previous investigators have been handicapped by the lack of a suitable manometric technique, and have employed the older chemical methods involving nitrogen and sugar analyses. Their experiments usually required several days or weeks, rather than a few hours, so that it was impossible to maintain constant, reproducible