Confocal scanning microscope image of Klebsiella pneumoniae growing on sand grains in a porous media flow cell. The organisms were inoculated in the "ultra-micro bacteria", starved, state and then revived by nutrient input. The bacteria cells were stained with the nucleic acid stain propidium iodide and appeared white against the darker sand grains. Pore water was stained with fluorescein and appeared grey. The biofilm caused a decrease in permeability, which in ground water may possibly be useful in the creation of "bio-barriers" to contain and remediate contaminant plumes.

Stoodley, P., de Beer, D., and Lewandowski, Z. 1994. Liquid flow in biofilm systems. Appl. Environ. Microbiol. 60:2711-2716.