UVC-INDUCED LYSIS AND DETRITUS PRODUCTION OF OSCILLATORIA-LIMNETICA IN A 2-STAGE CONTINUOUS-FLOW SYSTEM

In order to study in model systems the role of heterotrophic micro-org anisms in the aquatic microbial food web, a natural food source consis ting of senescent primary producer cells is indispensable. A two-stage continuous-flow system with the ability to produce detritus continuou sly is presented. In the first stage, a primary producer, i.e. the cya nobacterium Oscillatoria limnetica, was cultured. The second stage was fed with UVC-killed primary producer cells from the first stage. A co ntrol second stage received living primary producer cells. Both second stages were filled with prefiltered lake water in order to provide a natural inoculum of bacteria. During a 2 month experiment, the system was tested for its ability to produce detritus (first stage of detritu s, i.e. lysis of the cell material). Chlorophyll a concentrations prov ed to be adequate for calculating specific lysis rates. Very high spec ific lysis rates were found after killing the cells with UVC as compar ed to the control stage.