Bacteria: Hitchhiked through the water column

Microbes use Wasserfl he as Taxi by boundary layers in seawater

Bacteria use water fleas as "taxi" © IGB
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Bacteria occupy important functions in waters and contribute significantly to the metabolism and therefore to the self-purification of lakes. But how do the tiny creatures move between layers of water that are insurmountable to them alone? Researchers have now discovered the "trick" in experiments: The microbes use small aquatic animals as a transport opportunity to change layers of water.

Deep lakes mostly have zones with different living conditions. For example, near the water surface there are areas with increased concentrations of oxygen and organic material, for example algae, while inorganic nutrients are present at a higher concentration at depth. Most larger organisms in the water can move in the water column according to their needs. But microorganisms like bacteria can not do this. For them, many boundary layers in the body of water, which develop, for example, along temperature or chemical gradients, can not be overcome without outside help.

Sea coating replicated in the laboratory

Researchers from the working group of Hans-Peter Grossart from the Leibniz Institute of Freshwater Ecology and Inland Fisheries have now studied in cooperation with colleagues from the Virginia Institute of Marine Science how aquatic bacteria can overcome these barriers. Their goal: They wanted to test whether the conveyor belt hypothesis, according to which the microbes use other living things as a "taxi", stmmt.

For this, the researchers simulated the typical stratification of a lake in so-called migration columns and used water flea crabs (Daphnia magna) as a typical inhabitant of the water column. Then they isolated three different types of bacteria from Lake Stechlin, labeled them with green fluorescent protein (GFP) and placed them either in the upper or lower water layer of the migration columns.

Microbes actively jump on "taxis"

The observations showed that the water fleas actually acted as an effective means of transport for the bacteria. The microbes were actively transported by jumping on the Wasserflöhe. Up to one percent of the bacteria changed the water layer daily. The experiments also showed that the composition of the attached to water fleas bacterial communities according to their day and night migration significantly different. In the Nehmitzsee in Brandenburg, the scientists were able to prove their "conveyor belt hypothesis" in the field. display

The active attachment of microbes to various larger and migratory aquatic organisms has far-reaching ecological and evolutionary consequences. For now it has been proven that this actually enables an increased exchange of bacteria over a long distance.

(Forschungsverbund Berlin eV, 30.07.2010 - NPO)