Water flow through a bacterial biofilm was directly demonstrated by tracking fluorescent latex particles (0.28µm diameter) through biofilm channels. The biofilm—composed of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Klebsiella pneumoniae—was grown in a flow cell on a glass coverslip. The biofilm micro-colonies, or "cell clusters" were autofluorescent and appeared lighter than the surrounding water channels. The average flow velocity of the water through the flow cell was 6.6 cm/s (in the direction indicated by the arrow), but at the depth of 70µm in the 175 µm thick biofilm the particles were moving at velocities between 10 and 20 µm/s. The discovery that water can flow inside biofilms has important consequences for our understanding of fundamental biofilm processes.
Until recently it was generally assumed that water only flowed above the biofilm and that dissolved species, such as nutrients, waste products and antimicrobial agents, moved through the biofilm by diffusion alone, a much slower process. An open structure, with water flowing through the biofilm, presents a much more dynamic situation. Also, internal water flow within the biofilm implies that we should consider the influence of hydrodynamic drag on the detachment of individual cell clusters in addition to the fluid shear stress.
Movie sequence appears in:
de Beer D and Stoodley P, "Microbial biofilms," In: The Prokaryotes: An evolving electronic resource for the microbiological community, 3rd edition (release 3.4), New York, Springer-Verlag, 2000; [www.prokaryotes.com], Accessed 01/04/01 ISBN: 0-387-14254-1.
Microscopy: Bio-Rad MRC600 confocal scanning laser microscope attached to an upright Olympus BH2 microscope. Fluorescence imaging using a 20X objective. Scale bar=50 µm. The time-lapse sequence was taken over 44 seconds. Imaging was done at the Center for Biofilm Engineering, Montana State University, Bozeman, MT.
Movie Author: Stoodley P (1994_m02)
de Beer D and Stoodley P, "Relation between the structure of an aerobic biofilm and transport phenomena," Wat Sci Tech, 1995; 32:11-18.
Stoodley P, de Beer D, and Lewandowski Z, "Liquid flow in biofilm systems," Appl Environ Microbiol, 1994; 60:2711-2716. (Abstract not available.)
Stoodley P, de Beer D, Boyle JD, and Lappin-Scott HM, "Evolving perspectives of biofilm structure," Biofouling, 1999; 14:75-94.