UVC-induced lysis and detritus production of Oscillatoria limnetica in a two-stage continuous-flow system

In order to study in model systems the role of heterotrophic micro-organisms in the aquatic microbial food web, a natural food source consisting of senescent primary producer cells is indispensable. A two-stage continuous-flow system with the ability to produce detritus continuously is presented. In the first stage, a primary producer, i.e. the cyanobacterium Oscillatoria limnetica, was cultured. The second stage was fed with UVC-killed primary producer cells from the first stage. A control second stage received living primary producer cells. Both second stages were filled with prefitered 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 detritus, i.e. lysis of the cell material). Chlorophyll a concentrations proved to be adequate for calculating specific lysis rates. Very high specific lysis rates were found after killing the cells with UVC as compared to the control stage.