Transmission electron microscopy images of P. fluorescens EvS4-B1 biofilms (21 days). Specimens were prepared using cryomethods and embedded in resin. The sections represent regions of biofilm containing structured networks of fibers and sheets, but few bacteria. (A) The walls consisted of thin laminar structures (arrowhead) with globular material (arrow) accumulating in branching regions; scale bar = 500 nm. (B) In other regions of the biofilm, the wall-like structures had different thicknesses. The thin walls (arrowhead) were attached to thicker walls (arrow); scale bar = 500 nm. (C) Different wall morphologies consisted of thin, straight walls (arrowhead) branching from thicker walled structures (arrows); scale bar = 500 nm. (D) The thicker walls were composed of globular amorphous masses (arrows) covered in part by a distinct coating (arrowheads); scale bar = 200 nm. (E) and (F) The different components of the thicker walls consisted of globular masses (arrows) separated by and covered with thin coatings (arrowheads); scale bar = 500 nm.