Bacterial colonization of suspended solids in the River Danube

The River Danube was studied in the vicinity of Vienna (Austria) to examine the interactions among suspended matter, bacterial colonization and dissolved organic matter on a medium temporal and spatial scale. The concentration of suspended matter, the total number of particles and the number of bacteria attached to particles correlated with discharge rates. In the River Danube, 39% of the particles stained with Alcian Blue were colonized by bacteria, but only a small number of particles were heavily colonized. About 9.5% of the total bacterial community was found to be associated with particles; abundance of free-living bacteria varied between 2.4 and 7.8 × 10⁶ cells ml^-1 and attached bacterial abundance varied from 0.1 to 1.4 × 10⁶ cells ml^-1. On average, 8 bacteria particle^-1 were found in the River Danube. Smaller particles were colonized more densely by bacteria than larger particles. In the River Danube, 60% of the particles were found to be in the size range of >9 to 100 μm² and 57% of the attached bacteria colonized this size class.