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Aquatic Microbial Ecology

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AME 24:69-81 (2001)  -  doi:10.3354/ame024069

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

K. Barbeau*, E. B. Kujawinski**, J. W. Moffett***

Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
Present addresses: *Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA **Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA ***Corresponding author: E-mail:

ABSTRACT: To characterize trace metal cycling in marine systems as mediated by heterotrophic protists, we conducted a series of laboratory experiments in 2-organism model systems consisting of bacteria and protistan grazers. Trace metal isotopes (59Fe and 234Th), 14C, and bulk organic carbon measurements were used to follow the chemical transformation of bacterial carbon and associated trace metals by several different grazer species. Results indicate that grazers were able to cause repartitioning of Th and regeneration of Fe from bacterial prey into the dissolved phase (<0.2 μm), even in particle-rich laboratory cultures. For both Th and Fe, protist grazing led to the formation of relatively stable dissolved and colloidal metal-organic species. Metal/carbon ratios of the particle pool in some model systems with grazers were significantly altered, indicating a decoupling of trace metal and organic carbon cycling through the grazing process. Different protist species exhibited substantial variation (up to a factor of 10) in their ability to quantitatively remobilize trace metals from bacterial prey. The implications of these findings for trace metal cycling in marine systems are discussed.

KEY WORDS: Marine protists · Iron · Thorium · Organic carbon · Recycling

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