Live bacteria reduce fluid viscosity to zero

Nature : Theoretical models had predicted that a solution of microbes might be a superfluid—it could flow without friction. Now, Harold Auradou of the University of Paris-Sud in Orsay, France, and his colleagues have shown that the models are correct. The researchers put a solution of water, nutrients, and live E. coli into a rheometer, a device that spins the liquid and measures its viscosity. As they increased the E. coli concentration and tried different strains, they found that a solution with a very active strain of about 6 billion bacteria per milliliter reached a viscosity of zero. Increasing the concentration further did not change anything. However, using less active strains resulted in a higher viscosity, and using dead cells produced no change in viscosity at all. The theoretical models suggest it is the microscopic flagella the bacteria use to move around that causes the solution to become less viscous.