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Journal of Agricultural Rbsbarch Vol. 66 MARCH 15, 1943 No. 6 JOURNAL OF AGRICULTURAL RBSBARCH CONTENTS Page An Apparatus for Studying Respiration of Azotobacter in Relation to the Energy Involved in Nitrogen Fixation and Assimilation (Key No. Calif .-1^2) ' - - - " - - - - - - 229 J.M. FIFE Relationship of Certain Characteristics of Seed Cottons to Ginning . (Key JSÍO. M-3) - - - - - - - - - - - 249 W. SHARROTT SMITH, WILLIAM J. MARTIN* and NORMA L. PEARSON ISSUED BY AUTHORITY OF THE SECRETARY OF AGRICULTURE WITH THE COOPERATION OF THE ASSOQATION OF LAND-GRANT COLLEGES AND UNIVERSITIES For sale by the Superintendent of Documents, U» S. Government Minting Office Washington, D* C. - See page 2 of cover for prices JOINT COMMITTEE ON POLICY AND MANUSCRIPTS FOR THE UNITED STATES DEPARTMENT FOR THE ASSOCIATION OF lAND-GRANT OF AGRICULTURE COLLEGES AND UIíIVERSITIES P. N. ANNAND, CHAIRMAN V. R, GARDNER Chieff Bureau of Entomology and Plant Director^ Michigan Agricultural Experi- Quarantine^ Agricultural Research Ad- ment Station ministration JOHN W. ROBERTS C. B. HUTCHISON Principal Pathologist, Bureau of Plant Director^ California Agricultural Experi- Industry, Agricultural Research Ad- ment Stati&n, ministration BENJAMIN SCHWARTZ Principal Zoologist, Chief, Zoological Divi- W. H. MARTIN sion, Bureau of Animal Industry^ Directorf New Jersey Agricultural Ex- Agricultural Research Administration perimeTU Si(Uion EDITORIAL SUPERVISION M. C. MERRILL Chief of Publications, United States Department of Agriculture Articles for publication in the Journal must bear the formal approval of the chief of the department bureau, or of the director of the experiment station from which the paper emanates. Each manuscript must be accompanied by a state- ment that it has been read and approved by one or more persons (named) familiar with the subject. The data as represented by tables, graphs, summaries, and conclusions must be approved from the statistical viewpoint by someone (named) competent to judge. AH computations should be verified. Station manuscripts and correspondence concerning them should be addi*essed to V. R. Gardner, Director, Michigan Agricultural Experiment Station, East Lansing, Mich., who is chairman of the Station subcommittee. Published with the approval of the Director of the Budget. Issued on the 1st and 15th of each month. This volume will consist of 12 numbers and the contents and index. Subscription price: Entire Journal: Domestic, $3.25 a year (2 volumes) Foreign, $4.75 a year (2 volumes) Single numbers: Domestic, 15 cents Foreign, 20 cents Articles appearing in the Journal are printed separately and can be obtained by purchase at Scents a copy domestic; 8 cents foreign. When purchased in quantity of 100 or more, a reduction of 25 percent in the cost will be made. If separates are desired in quantity, they should be ordered at the time the manu- script is sent to the printer. Address all correspondence regarding subscriptions; and purchase of numbers and separates to the Superintendent of Documents, Government Printing Office, Washington, D. C. JOIMALOFAGKICOmiRAlESEARCH VOL. 66 WASHINGTON, D. C, MARCH 15, 1943 No. 6 AN APPARATUS FOR STUDYING RESPIRATION OF AZOTO- BACTER IN RELATION TO THE ENERGY INVOLVED IN NITROGEN FIXATION AND ASSIMILATION ' By J. M. FIFE 2 National Research Council fellow in the biological sciences, 1927-29, Division of Plant Nutrition and the Department of Chemistry, California, Agricultural Experiment Station INTRODUCTION The discovery of Azotohader by Beijerinck (i) Hn 1901, encouraged a vast amount of work on the physiology on this group of nitrogen- fixing bacteria. Since the free-energy data pubhshed by Lewis and Randall {10) appeared, the interest of other investigators (5, 6, 7, 12, 13) in these organisms has centered on the energetics and efficiency of the nitrogen-fixation process, the efficiency of growth, and also on the efficiency of oxygen utilization. Studies on the rate of respiration of Azotohader, while being sub- jected to a wide range of carefully controlled environmental conditions, were started in August 1929, at Berkeley, Calif., and continued during the following 2 years. In this paper the apparatus and methods used are described and certain of the results of the investigations are presented. The chemical reactions catalyzed by Azotohader to obtain the neces- sary energy for its metabolic processes vary greatly. Under aerobic conditions the oxidation of glucose to carbon dioxide and water is a typical reaction which is catalyzed by these organisms. It may be written, using the terminology of Lewis and Randall {10), C6Hi206+602=6C02+6H20;AH=-674,000 cal. The rate at which this reaction is carried out may be considered a direct measure of the metaboUc activity of the culture. Consequently the rate of respiration of a culture of Azotohader under different environmental conditions can be determined by measuring the rate at which this reaction proceeds. This rate may be measured in either of two ways: (1) by measuring the rate of disappearance of the reacting substances, such as the rate of absorption of oxygen; (2) by measuring the rate of formation of the end product, carbon dioxide, or the heat of the reaction. As long as the organismos are utilizing free oxygen, as opposed to combined oxygen, in the reactions catalyzed for a source of energy, a measure of either the rate of oxygen consumption or the rate of carbon dioxide production or the rate at which heat is evolved will give an accurate index to its metabolic activity. 1 Received for publication January 12, 1942. This investigation was made possible by the >3ational 2 The author is indebted to G. N. Lewis, Merle Randall, D. R. Hoagland, A. R. Davis, and C.B. Lipman, of the university staff, and to F. C. Steward, of the Department of Botany, Birkbeck College, University of London, for interest shown in the work and for valuable suggestions and criticisms. 3 Italic numbers in parentheses refer to Literature Cited, p. 248. Journal of Agricultural Research, Vol- ö6, No. 6 Washingtonw asnmgion, Du.^. C ^^^March ^^ 15,Calif.-132 1943 514451—43 1 ■ (229) 230 Journal of Agricultural Research voi. 66, No. 6 However, there is evidence (2, 9) that Azotohacier catalyzes energy- Hberating reactions not involving free oxygen under anaerobic or partly anaerobic conditions. This has been confirmed by the author. Under such conditions, the rate at which the reaction proceeds does not give a complete measure of the metabolic activity of the culture or an indication of the total energy liberated. Consequently, experi- ments at low oxygen tensions in which only the rate of free oxygen utilization or the rate of carbon dioxide production is measured would be of little value in determining the efficiency of growth or of oxygen utilization per cell or the efficiency of the nitrogen-fixation process. CRITIQUE OF METHODS Most of the earlier work on the physiology of Azotohacier with respect to oxygen utilization and carbon dioxide production was done with a qualitative outlook and was carried out with few if any precau- tions taken to keep the partial pressure of oxygen and carbon dioxide in the culture constant. Nor was this work done in such a way that the reactions catalyzed by the organisms would proceed at a maxi- mum rate under the conditions imposed. The methods in these respiration studies were in general inadequate to give an accurate picture of the metabolic activity of Azotobacter over relatively short periods under carefully controlled conditions. This critique of the methods may be said to be especially valid where respiration studies were conducted with partial pressures of oxygen which deviated con- siderably from that in air. It will be desirable at this point to discuss certain methods used by later investigators. A consideration of their results will be post- poned until after the discussion of the experimental results presented in this paper. Bonazzi (2) made a study of the oxygen consumption oí Azotobacter, In one experiment 2,566 cc. of air was confined over 100 cc. of an inoc- ulated culture medium ^nd incubated for 52 days. From table 4, page 339, of Bonazzi's paper, it is evident that the partial pressure of the gases in the system varied greatly. In this experiment, the con- centration oí CO2 in the air above the culture increased 160-fold during the experiment. At the same time the partial pressure of oxygen decreased to one-twentieth. The composition of the medium with respect to certain ions was similarly changed. There were 44.36 mg. of CO2 dissolved in the 100 cc. of medium at the end of the experiment, making the medium 0.01 molal with respect to carbonic acid. As there were only 0.02 gm. of K2HPO4 (0.001 molal) to serve as a buffer, this concentration of carbonic acid, which would not be affected much by the other salts present, would bring the pH of the medium to about 5.5. There would result approximately a 300-fold change in the hydrogen-ion concentration. It is evident that the question of equilibrium was not taken into consideration in these experiments. During the first few hours in such experiments the available oxygen and carbon dioxide con- centration might have permitted a rapid aerobic respiration, but the conditions would soon have become more favorable for anaerobic respiration than for aerobic respii-ation. Meyerhof and Burk (13) and Lineweaver, Burk, and Horner (11) have made an extensive study of the physiology of Azotobacter by the use of the Warburg technique (IS). Mar. 15,1943 Apparatus fOf Studying Respiration of Azotohacter 231 The total volume of the apparatus used (4, 6) was about 12 to 16 cc. For the removal of carbon dioxide, these investigators relied entirely upon the normal rate of diffusion of the gas from an alkaline medium (buffered usually at pH 7.3) into the confined atmosphere above, aided only by a gentle rocking of the entire apparatus.
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