Role of ciliates, flagellates and bacteriophages on the mortality of marine bacteria and on dissolved-DNA concentration in laboratory experimental systems

Several marine bacteriophages, a ciliate (Uronema sp.), and a flagellate (Pseudobodo sp.) were used to study comparatively the grazing and clearance rates of four marine bacteria. Bacteria were fluorescently labelled using rhodamine isothiocyanate. The results obtained indicate that bacteriophages and flagellates caused a significantly higher (P < 0.025) decrease in the number of marine bacteria compared to the ciliate Uronema sp. The role of bacteriophages, ciliates and flagellates in the production of dissolved-DNA (D-DNA) was also studied. The interaction between both bacteriophages and protists with marine bacteria are responsible for an increase of the D-DNA concentration, although a direct relationship between D-DNA concentration and predator number was only obtained from experiments performed with Uronema sp. (C) 2000 Elsevier Science B.V. All rights reserved.