| Summary: | Iron has been widely recognized as a potentially key factor in promoting nitrogen fixation by Trichodesmium. Data from both laboratory and field studies demonstrates that increasing the iron concentrations stimulates growth, photosynthetic rates and nitrogen fixation of both cultured and natural populations. However, quantitative studies that elucidate relationships between cellular iron quotas and physiological mechanisms have been limited. In this study, molecular techniques enabled quantification of the amount of nitrogenase expressed in iron-replete cultures of Trichodesmium IMS 101 over a diel cycle. A standard of the purified iron component of nitrogenase was generated from an expression and protein purification system. Using this standard and known values of intracellular carbon, the amount of nitrogenase per carbon at peak expression was measured, 0.038 mg nitrogenase: mg C. The quantity of iron bound in the nitrogenase structure was then calculated; Fe:C equal to 236.53 [mu]mol: mol. Using estimates of Trichodesmium biomass from the literature, the amount of iron bound in the nitrogenase structure was calculated for various ocean regions, resulting in 2.22 [mu]mol m-3 and 0.05 [mu]mol m-3 of iron bound in nitrogenase in the subtropical North Atlantic and North Pacific, respectively. M.S. Includes bibliographical references (p. 29-32) by Sherrie Whittaker
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