Growth response of a marine phytoplankton Coccolithus huxleyi to various chemical forms of cobalt

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