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Séminaire de Stephan Herminghaus

Biofilms : does Kinneyia predate the evolution of mechanoresponse ?

Stephan Herminghaus

MPI Göttingen, Germany

Biofilms are the oldest multi-cellular structures in earth’s history, and ubiquitous still today. In the fossil record, there are structures called Kinneyia, characterized by a pronounced ripple pattern, which are known to represent ancient ( 600 My) microbial mats. To date there has been no conclusive explanation as to the processes involved in the formation of these fossils. As microbial mats have been reported to behave like visco-elastic fluids, we propose that the key mechanism involved in the formation of Kinneyia is a Kelvin-Helmholtz instability induced in a visco-elastic film under flowing water. Experiments carried out using model visco-elastic films (a goo made from PVA and borax) support this idea. As predicted by theory, the ripple pattern that forms has a wavelength roughly three times the thickness of the film, independent of the viscosity of the film and the flow conditions. Well-ordered patterns form, with both honeycomb-like and parallel ridges being observed, depending on the flow speed. These patterns correspond well with those found in Kinneyia fossils, with similar morphologies, wavelengths and amplitudes being observed. Interestingly, such ripple structures have not been observed on any recent microbial mat. An interesting interpretation of this absence is that the ubiquitous mechano-response of virtually all eucariotic cells may stall the Kelvin-Helmholtz instability. This could then be taken as evidence that the Kinneyia fossil predates the evolution of mechano-response.