Bremen, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

University, Diss., 2002--Bremen.

Three species of photosynthetic flagellates capable of phagotrophy (mixotrophic species) were tested for their abilities to use inorganic iron colloids for growth. Ochromonas sp., Chrysochromulina ericina (a coastal strain) and C. ericina (an oceanic strain) were grown in iron-free seawater supplemented with 1 muM goethite, hematite, magnetite/maghemite or ferrihydrite (90°) in the presence and absence of desferrioxamme B, an iron-binding siderophore. Both strains of Chrysochromulina grew at 35--70% of their maximum rates with goethite, hematite, and magnetite/maghemite, but were unable to use ferrihydrite. Ochromonas, however, grew well with ferrihydrite, but could not use any of the other forms. All the flagellates were able to acquire iron from ingested bacteria. Diatoms that were known only to take up dissolved forms of iron, Thalassiosira oceanica (clone 1003) and T. pseudonana (clone 3H), were unable to use any of the colloids tested. The mechanism of iron acquisition by the flagellates appeared to involve ingestion of the iron colloids as DFB had no effect on colloidal iron availability and bacteria resident in the cultures were unable to use the iron contained in the colloids. Variations in the size of the colloids were hypothesized to account for differences in their availability, independent of colloid chemical stability. The results provide the first strong evidence for direct utilization (i.e. without prior dissolution) of colloidal iron by mixotrophic phytoplankton and document a new pathway of iron acquisition that may be important for their survival in low-iron waters of the sea.

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