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Center for Biofilm Engineering
Movie Description:
Liquid flow through biofilm channels
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| 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 to appear in The Prokaryotes (deBeer, D. and Stoodley,
P. 2000. "Microbial Biofilms", in Dworkin, M., Falkow, S., Rosenberg,
E., Schleifer, K., and Stackebrandt, E., eds. The Prokaryotes: An
evolving electronic resource for the microbiological community, 3rd
edition (release 3.4), Springer-Verlag, New York,) and used with
permission.
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: P. Stoodley
Further Reading:
deBeer, D. and Stoodley, P. 1995.
Relation between the
structure of an aerobic biofilm and transport phenomena. Wat. Sci.
Tech. 32:11-18.
Stoodley, P., de Beer, D., and Lewandowski, Z. 1994. Liquid flow in
biofilm systems. Appl. Environ. Microbiol. 60:2711-2716.
Stoodley, P., deBeer, D., Boyle, J.D., and Lappin-Scott, H.M. 1999.
Evolving perspectives of
biofilm structure. Biofouling 14:75-94.
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3D view of water flowing through a bacterial biofilm
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| Confocal scanning laser microscopy image series of
a bacterial biofilm composed of Pseudomonas aeruginosa,
Pseudomonas fluorescens, and Klebsiella pneumoniae.
Fluorescent particles were added to the bulk liquid to allow
flow visualization and quantification. In this movie sequence
the beads appeared as dashed lines as they flowed around biofilm
cell clusters. The faster moving particles, which were further
away from the substratum, left longer tracks than the slower
moving particles. The velocity of the particles were calculated
from the length of the track to determine the velocity profile
and wall shear stress in the biofilm.
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The bacterial cells were stained with the nucleic acid stain
propidium iodide. At the low magnification, used to
construct this sequence, the individual cells were not seen but
the cell clusters appeared as bright patches. Fluorescent
particles were clearly seen flowing through the water channels
between the cell clusters. These observation confirmed the
speculation that water could flow through biofilms. Dissolved
oxygen measurements (made with microelectrodes) showed that the
water channels could enhance the supply of oxygen to the
bacterial cells. The fact that the biofilm structure appeared to
be beneficial to the cells in the biofilm prompted
biofilmologists to speculate that the structure may be
controlled largely by the organisms themselves. Similar
structures can also be explained by the physical-chemical
conditions of the local environment. The relative contribution
of the extent to which structure is determined by either the
external environment or by genetic control is currently under
debate. Microscopy: The image was taken with a Bio-Rad MRC600
CSLM attached to an Olympus BH2 microscope using a 20X
objective. Scale bar = 100 µm. The rocking motion is an artifact
required to give the 3D effect.
Movie Author: P. Stoodley
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| Further Reading:
deBeer, D. and Stoodley, P. 1995.
Relation between the
structure of an aerobic biofilm and transport phenomena. Wat. Sci.
Tech. 32:11-18.
Stoodley, P., de Beer, D., and Lewandowski, Z. 1994. Liquid flow in
biofilm systems. Appl. Environ. Microbiol. 60:2711-2716.
Stoodley, P., deBeer, D., Boyle, J.D., and Lappin-Scott, H.M. 1999.
Evolving perspectives of
biofilm structure. Biofouling 14:75-94.
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