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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 967

David A. Caron; Grazing of attached bacteria by heterotrophic microflagellates. Microbial Ecology 13:203-218, 1987

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Four species of heterotrophic microflagellates were examined for their ability to graze attached and unattached bacteria. The species tested displayed pronounced differences in their ability to graze the bacterium Pseudomonas halodurans attached to chitin particles. Two species of microflagellates (Monas and Cryptobia sp.) efficiently grazed unattached bacteria but showed little or no ability to graze attached or aggregated cells. In contrast, Rhynchomonas nasuta and Bodo sp. showed marked preferences for attached and aggregated bacteria and a limited ability to graze unattached cells. The density of attached bacteria was reduced by an order of magnitude due to grazing by Bodo and R. nasuta, even though the density of unattached bacteria was ~5-90x the density of attached cells. The maximum densities attained by microflagellates in the cultures were related to the density of unattached bacteria for Monas and Cryptobia but not for Bodo and R. nasuta. Growth of the latter two species appeared to be related to the density of attached or aggregated bacteria. Based on the results of these experiments, it is concluded that the pelagic existence of microflagellates that graze attached bacteria may be strongly linked to the distribution of suspended particles and their associated bacteria. In addition, the removal of attached bacteria by microflagellates can significantly affect the density of bacteria attached to particles in the plankton. This activity may have important implications for the controversy concerning the relative importance of attached and free-living bacteria in the plankton.