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The detection and characterization of bacteria-sized protists in “Protist-free” filtrates and their potential impact on experimental marine ecology

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Abstract

Nuclepore filters of 0.6–1.0μm pore size have been used to prepare “protist-free” water for a number of studies in microbial ecology. This procedure has been called into question by a recent study claiming that a significant portion of bacterial loss in filtrates could be due to uncharacterized predators passing through 0.6μm filters. We were unable to directly observe protists in 0.6μm filtrates using phase contrast, epifluorescence, or transmission electron microscopy. Using the culture techniques of rice grain enrichment and most probable number, however, we were able to observe and quantify several species of bacterivorous nanoflagellates that developed not only in 0.6μm, but also in 0.4μm seawater filtrates. The ability of predacious nanoflagellates to squeeze through bacteria-sized pores questions studies of bacterial production and chemical cycling that have assumed protist-free filtrates.

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Authors and Affiliations

  1. Graduate School of Oceanography, University of Rhode Island, Narragansett, 02882, Rhode Island

    F. J. Cynar, K. W. Estep & J. McN Sieburth

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  1. F. J. Cynar
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  2. K. W. Estep
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  3. J. McN Sieburth
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Cynar, F.J., Estep, K.W. & Sieburth, J.M. The detection and characterization of bacteria-sized protists in “Protist-free” filtrates and their potential impact on experimental marine ecology. Microb Ecol 11, 281–288 (1985). https://doi.org/10.1007/BF02016812

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