DEGRADATION OF ALGAL EXUDATES BY MIXED BACTERIAL BIOCENOSES

In the frame of a research project concerning regrowth problems a wate r utility at Lake Constance is involved. For this plant it was interes ting to find out which effect is exerted by organic products released from algae living in the lake water. Therefore model experiments were carried out using two different algal cultures in the stationary phase , where the algas were carefully separated by filtration. From these e xtracellular organic carbon solutions (exudates) dilutions were prepar ed using highly purified deionized water. These were tested for their ability to support bacterial growth by adding a mixed bacterial biocen osis after sterile filtration and monitoring growth curves by turbidit y measurements, a method developed at the DVGW-Research-Center in Karl sruhe to judge drinking water with respect to its regrowth potential. It was shown that the exudate from a Haematococcus culture is very gro wth stimulating, though the substrate concentration analyzed as DELTAD OC was very low. In contrast the exudate from a Stephanodiscus culture gave a very low growth response. The effect of the Stephanodiscus cul ture for the drinking water plant at Lake Constance is much more impor tant because Stephanodiscus is a species common in Lake Constance wher eas Haematococcus is not.