The formation of microcolonies by rumen bacteria

When rumen fluid is fixed for electron microscopy, without centrifugation, a large amount of material sediments spontaneously and ruthenium red staining shows this material to be partially composed of bacterial microcolonies in which morphologically similar sister cells are enclosed in an extensive fibrous exopolysaccharide glycocalyx. The exopolysaccharide matrix condenses, to variable degrees, during the dehydration steps of specimen preparation for electron microscopy but some fibers are stabilized by their attachment to solid surfaces at multiple points and the extent of this matrix can be deduced from morphological data. Even after condensation, the glycocalyces of rumen bacteria occupy more space than the cells themselves and they completely surround most cells with a fibrous matrix, whose chemical composition dictates an ion-exchange function, that must be assumed to be protective against some bacteriophage and antibacterial agents.