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 (P seudobodo sp.) were used to study comparatively the grazing and clearance r ates of four marine bacteria. Bacteria were fluorescently labelled using rh odamine isothiocyanate. The results obtained indicate that bacteriophages a nd flagellates caused a significantly higher (P < 0.025) decrease in the nu mber of marine bacteria compared to the ciliate Uronema sp. The role of bac teriophages, ciliates and flagellates in the production of dissolved-DNA (D -DNA) was also studied. The interaction between both bacteriophages and pro tists with marine bacteria are responsible for an increase of the D-DNA con centration, although a direct relationship between D-DNA concentration and predator number was only obtained from experiments performed with Uronema s p. (C) 2000 Elsevier Science B.V. All rights reserved.