Scanning electron micrographs of P. fluorescens EvS4-B1 biofilms (14 days) prepared using cryomethods. (A). Fibrillary structures appeared to be made up of twisted fibers (arrow) scale bar = 1 μm. (B). Flat sheets of material (arrowhead) also were observed. Some of the sheets seemed to be wrapped around other structures (arrow); scale bar = 20 μm. (C) The inside core of the "wrapped" structures consisted of bacteria, [B], embedded in an extracellular matrix of particulate matter and a thin sheet of material (arrow); scale bar = 1 μm. (D) The outer sheet (arrowheads) enveloped an inner core consisting of fibers forming irregular network-like structures (arrow); scale bar = 10 μm. (E) The network consisted of fibers arranged in a periodic pattern. The bacteria (arrows) were two to three times larger than the spaces in the network; scale bar = 2 μm. (F) A sheet of material, [S], covered the fiber network and was attached to it. The fibers were associated with bacteria, [B], and particulate matter, [P]; scale bar = 2 μm.