Biology Reference
In-Depth Information
gel-like characteristics, which make them dificult to image with scanning
probes. One study of bioilm organization, imaged in air, examined a number
of surface protein mutants of
the primary cause of
tooth decay in humans. 70 Investigations of the bioilm matrix components
curli (which are amyloid ibres), cellulose and the cell surface protein BapA
in bioilm and colony morphology of
Streptococcus mutans
,
indicate that
curli and cellulose but not BapA have an impact on the formation and the
morphology of a bioilm. 71 When compared with cellulose, curli appears to be
more important for the formation of cell aggregates. 71
The adhesive properties and spring constants of bioilms derived from
four different bacteria (
Salmonella typhimurim
grown on
glass were examined in liquid. 57 This study showed that the spring constant of
bacteria in a bioilm was higher than that for the same strain that was grown
in liquid. 57 A study examining the effect of a range of inorganic compounds on
S. epidermidis
P. putida, E. coli, M. luteus and B. subtilis)
bioilm formation revealed that, while the compounds did not
signiicantly affect the growth of an already established bioilm, they had a
strong inhibitory effect on initial bacterial adhesion. 72
The survival of bioilms exposed to
a Gram-
negative bacterium that preys on other Gram-negative bacteria, was found
to correlate with the nutritional level of the growth media. In nutrition poor
media
Bdellovibrio bacteriovorus,
Bdellovibrio
completely killed the bioilm, whereas in rich media some
E. coli
would remain. 73 In an earlier study, the same authors proposed that
predation behaviour at interfaces (air-solid or liquid-solid) differed from
those in solution. They simulated the air-solid interface by growing the
bacteria on sterilized, small-pore ilters placed on agar plates. Over a period
of a few days, several life cycles of
Bdellovibrio
were imaged in air by AFM.
When
, they utilized the prey's macromolecules
for growth. During this period, the combined organism is called a bdelloplast.
In electron microscopy studies, unaffected prey could be distinguished based
on changes in their two-dimensional shape, but this study provided evidence
that there were also changes in the height of the structures. Speciically,
bdelloplasts were shown to be “rounded up” and smoother when compared
with uninvaded cells. The ability to image these cells without ixation was
important to the indings in this study because it allowed the researchers to
distinguish between true features and electron microscopy artefacts. 74
A related application is the use of AFM to evaluate cell-cell interactions
between microbes and eukaryotic cells. The interaction of
Bdellovibrio
invaded
E. coli
with mouse
bladder tissue has been studied by AFM in liquid and showed clusters of
bacteria trapped in the intermediate ilaments of the urothelial cells. 75 The
AFM images in liquid show
E. coli
in early stages of the infection to be loosely
organized in the bladder, but later bacteria become more tightly packed in
bioilm-like clusters among the ilaments of the bladder tissue.
E. coli
 
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