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Bacteria skedaddle when relatives start dying

The deaths of nearby relatives have a curious effect on the bacterium Caulobacter crescentus—surviving cells lose their stickiness.

Harmless Caulobacter live in nutrient-poor, aqueous environments like lakes, rivers, and even tap water. Like many other bacteria, Caulobacter form biofilms, aggregations of cells held in place by a sticky matrix produced by the bacteria themselves.

Bacteria in biofilms are more resistant to predators and to antibiotics, and are less affected by environmental stress. However, if environmental conditions worsen, it becomes advantageous for the bacteria to get away.

That presents a special problem for Caulobacter. In 2006, biologist Yves Brun, the project’s principal investigator, and Brown University colleagues learned that the sugar-protein glue the bacteria use to attach themselves to the biofilm matrix is the strongest adhesive known in nature. Once a cell joins the collective, it is stuck there.

Caulobacter solves the problem of getting stuck in poor conditions by producing a clone of itself through cell replication. The mother cell heroically stays behind. But the daughter cell, called the “swarmer,” starts out life with a flagellum, allowing it to move through water.

The daughter has the option of swimming away from its mother and its relatives in the biofilm, or of settling in the same biofilm where it was born.

The new findings reported in the journal Molecular Microbiology show that exposure to the extracellular DNA (eDNA) released by dying neighbors stops the sticky holdfasts of living Caulobacter from adhering to surfaces, preventing cells from joining bacterial biofilms.
 
 

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