The biofilm mode of life is only possible because biofilm organisms are transiently immobilized in a matrix of extracellular polymeric substances (EPS), also known as "slime". The matrix can be considered an emerging property of microorganisms, allowing them to form stable synergistic consortia, supporting interaction by signaling molecules and horizontal gene transfer and, eventually being activated by extracellular enzymes which turn the matrix into an external digestion system. As unsightly it is, this matrix is--although seemingly stochastic--a highly differentiated and functional immediate environment for biofilm cells.
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