Biomedical Engineering Reference
In-Depth Information
FIGURE 21.8
Hexagonally packed intermediate (HPI) layer from Deinococcus
radiodurans [20] .
21.6 AFM IMAGING OF MICROORGANISMS
More recently, the atomic force microscope has opened a new path for the investigation and manipu-
lation of structures on a very small scale. One of the most often cited advantages of the atomic force
microscopy (AFM) in the study of biological structures is the fact that, unlike electron microscopy,
high-resolution images can be obtained under physiological conditions. However, there is more to
the AFM than just its capacity for high-resolution imaging. The mechanical nature of AFM means
that the cantilever, used for imaging, can also be used to measure interaction forces in the piconewton
range.
As such, not only can the AFM image the surface of microorganisms at high resolution, under
physiological conditions, it can also be used to investigate the binding forces between microorgan-
isms and target surfaces.
21.6.1 Yeast
Saccharomyces cerevisiae , also known as budding yeast, is not only of use in industrial processes
from bread making to beer brewing, but it is also a type organism used in the study of eukaryotic
cells. The yeast S. cerevisiae is surrounded by a cell wall composed of proteins, polysaccharides, and
small amounts of chitin. Electron microscopy has shown that this cell wall is a layered structure rang-
ing up to 300 nm thick. When imaged with AFM, the surface of the cell appears very smooth and is
easily deformed, necessitating careful scanning at minimal force ( Figure 21.9 ). The only apparent
surface feature is the bud scar at the opposite end of the mother cell to the newly forming daughter
cell. The surface appears smooth as the sugars obscure the membrane.
 
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