Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School



The effect on nitrogen fixation of additions of washings and the dialysate derived from the Aerobacter aerogenes culture fixing nitrogen has been studied. The effects on nitrogen fixation of limited supplements of casein hydrolysate and ammonium acetate as sole sources of nitrogen and in combination have been compared. Data has been presented to show that addition of washings or the dialysate to the growth medium stimulates nitrogen fixation. Similarly, in the presence of casein hydrolysate, the starved and the nonstarved cells fixed nitrogen much earlier than the control cultures with no supplements of exogenous nitrogen. On the other hand, in the presence of added ammoniacal nitrogen diauxic growth was exhibited. On mixed supplements of casein hydrolysate and ammonium acetate diauxic lag was suppressed to a lesser or greater extent, depending on the amount of ammoniacal nitrogen present in the medium. The duration of the diauxic lag and the amount of ammoniacal nitrogen in the medium bore a direct relationship to each other. Aspartic acid had an effect similar to that of casein hydrolysate on nitrogen fixation. The data has been discussed in relationship to the other adaptive systems. Indications are that the nitrogenase system in this strain of A. aerogenes is inducible. Casein hydrolysate seems to stimulate the activity of nitrogenase, whereas ammoniacal nitrogen seems to repress it. The diauxic lag seems to represent the period during which the enzyme protein is increasing without any detectable cell growth.

Library of Congress Subject Headings

Nitrogen -- Fixation
Nitrogen-fixing microorganisms


Includes bibliographical references



Number of Pages