Original paper

Microbiological investigations in the river Danube: Measuring microbial activities and biomass

Kasimir, G. D.


Bacterial numbers, biomass and production estimates were performed in the impoundment of Altenwörth (Austrian part of the Danube) and in a longitudinal profile of the Danube between stream kilometers 16 and 1934. For production estimates, two approaches were compared. The frequency of dividing cells (FDC) approach gave higher estimates compared with the thymidine incorporation approach. The two approaches showed no parallel results, FDC seems to reflect past activities of allochthonous bacteria in their indigenous biotopes. Bacterial numbers and biomass were in the range of other big rivers and showed an increase from upstream to downstream. This trend is disturbed during HQ-situations, however. The discharge has the greatest impact on the system and superimposes other influences. A large part of the bacteria originate from soil biotopes. In spite of the long generation times (up to 5 days), bacterial production is high enough to allow the production of a considerable part of the existing bacterial biomass within the Danube. Particle-bound bacteria represent a high percentage (up to 43%) of the entire bacterial count. A high percentage of the bacteria is extremely small. Heterotrophic nanoflagellates are present in such numbers in the Danube that they probably exert pressure on the bacterial population.


river DanubeMicrobiological investigationbiomassbacterial numbersbacterial production