โ Scribed by Cox, Rosalie M.
No coin nor oath required. For personal study only.
In long-term experiments, nitrogen fixation in photosynthetic organisms is usually dependent upon the presence of light (FoGG and THAN TUN, 1960; F_au and FOGG, 1962) although certain photosynthetic nitrogen-fixers can grow and fix nitrogen in the dark using organic media (Nostoc muscorum, ALLISON, Hoovv,~, and MorRIS, 1937; Chlorogloea ]ritschii, FAY, 1965). One obvious dependency of nitrogen fixation upon light is for a source of carbon skeletons to assimilate the fixed nitrogen. There have, however, also been suggestions that the requirement of reducing power and energy for nitrogen reduction may also be supplied by light energy. Such suggestions have been made for Chromatium sp. (A~o~, LOSADA, NOZAKI, and TAGAWA, 1961), Rhodospirillum rubrum (P~AT~ and F~E~EL, 1959), Chlorogloea/ritschii (FAY and FOGG, 1962) and Anabaena cylindrica (FGGG and THAN TUN, 1958 ; COBB and MYERS, 1964). FOCG and THAW TuN (1958) found that more oxygen was evolved in the light under nitrogen-fixing conditions than by cells incubated under argon, an effect interpreted as a photoreduction of nitrogen using water as the hydrogen donor. However, THAN TuN and HARnIS (quoted FooG, 1961) found that after 12 hours' illumination, A. cylindrica could fix 15N 2 also in the dark.
Since it was possible to observe nitrogen fixation in the dark, it was thought worthwhile to investigate more fully the short-term relationships between nitrogen fixation and photosynthesis. On a long-term basis, carbon and nitrogen uptake arc closely related (FoGG and THAN TUN, 1960) but short-term experiments should give some clue to the nature of this relationship. Methods
Culture technique and nitrogen starvation. Bacteria-free bulk cultures of A. eylindrica (Cambridge Culture Collection No. 1403/2), were grown in a standard nitrogenfree medium (ALL]~ and A~o~, 1955) in Carel flasks. These were shaken continously on the apparatus described by Fo~G, S~xT~ and M~L~R (1959) at a rate of 70 oscillations/rain and a temperature of 25 ~ C. Continuous illumination at a light intensity of 350 foot-candles was provided by a bank of fluorescent tubes. Nine day-old cultures were harvested by centrifngation, then the Mgal material from about a ]itre of medium was bulked and resuspended in 25 ml of fresh sterile medium.
Oxygen evolution in the light was more rapid ia the presence of nitrogen than in argon, as observed also by FOGG and T~AN TuN (1958).
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Anabaena cylindrica grown in steady state continuous culture has an extractable ATP pool, measured on the basis of the luciferin-luciferase assay of 165 +/- 35 nmoles ATP mg chla-1. This pool is maintained by a dynamic balance between the rate of ATP synthesis and the rate of ATP utilization. Phosph
## Abstract Experiments were conducted to study the effect of five different organic substrates viz. lactose, fructose, mannose, xylose and sodium acetate on the heterotrophic growth characteristics with emphasis on growth, pigment composition, heterocyst frequency and nitrogen fixation of __Anabae