Vertical structure of microbial community in an eutrophic meromictic Saline Lake

Vertical variations of autotrophic picoplankton, heterotrophic bacteria, pigmented (PNAN) and non-pigmented (HNAN) nanoflagellates, and their activity were studied in a small-eutrophicated meromictic saline lake (eastern Adriatic Sea). The variations of heterotrophic filamentous cells exhibited similar patterns to that of HNAN, pointing out the ecological importance of the elongated cells. High concentrations of DOC and SAS in the chemocline stimulated the heterotrophic bacteria to increase their abundance and activity. Bacterial community in the chemocline layer was represented by higher proportions of high DNA-content cells, but with a rather low bacterial production per cell. In the surface layers, bacteria were less abundant, but had a very high production per cell. The large differences in the percentage of active cells between aerobic and anaerobic layers imply the possibility that different mechanisms structure the bacterial communities in these layers.