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The results of a preliminary experiment suggested that a complexed form of cobalt was more efficacious in promoting growth of a marine phytoplankton than ionic cobalt. The phytoplankton used in this experiment was Coccolithus huxleyi, a vitamin B₁₂ producer, and the cobalt complex was cobalt (II)- ethylenediaminetetracetic acid [Co(II)- EDTA]. A review of the biochemistry of vitamin B₁₂ indicates that a B₁₂ producer might prefer, if not require, Co(III) instead of Co(II). Since some of the Co(II)-EDTA in the preliminary experiment might have become oxidized to Co(III)-EDTA, the observed stimulation of growth could have been due to Co(III)-EDTA. Two experiments were performed to determine if Co(III)-EDTA is more efficacious in stimulating growth than Co(II)-EDTA. Coccolithus huxleyi, grown in batch cultures with constant illumination, was used in both experiments. One experiment had cobalt concentrations of 10 and 1 μg/l; the other had concentrations of 1 and 0.1 μg/1. In both experiments there were no observed differences in specific growth rates between treatments of Co(III) as the EDTA complex with 10⁻⁶ M additional EDTA and Co(II) with 10⁻⁶ M EDTA. Both of these treatments resulted in a specific growth rate larger than controls without added EDTA or cobalt. It is not possible to measure the amount of Co(II)-EDTA that is oxidized to Co(III)-EDTA at the concentrations used in these experiments. Consequently these results cannot be used as a basis for rejecting the hypothesis that Co(III) is the required form of cobalt. Since Co(III)-EDTA without the additional 10⁻⁶ M EDTA was apparently able to stimulate growth in relation to the controls, it is assumed that C. huxleyi is capable of utilizing this form of cobalt. / Graduation date: 1975

Call number: LD2668 .T4 1950 H5 / Master of Science

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Call number: LD2668 .T4 1952 J61 / Master of Science