Biology Reference
In-Depth Information
aeruginosa,
Bacillus atrophaeus.
28,30,31,41
It has
also been useful for immobilizing and imaging of diatoms.
42
Although gelatin-
coated mica has been used successfully for a number of microbial imaging
studies, not all bacteria have surfaces compatible with immobilization on
gelatin. Even within a species, variations in surface characteristics can
decrease the afinity of a microbe for the substrate. Further, the presence of
rich media or buffer salts can interfere with bacterial adhesion to gelatin-
coated surfaces.
Other cationic surface coatings have been prepared using amino-
containing silane reagents, poly-
Listeria monocytogenes
and
-lysine and other cationic polymers to
electrostatically immobilize bacteria. For example, poly-
L
L
-lysine has been
used to immobilize Gram-negative bacteria, including
E. coli, Shewanella
oneidensis, Burkholderia cepacia,
P. aeruginosa, Geobacter sulfurreducens
and Gram-positive
.
16,43-45
Glass slides coated with
polyethylenimine have been useful for immobilization and imaging
Listeria ivanovii
in
liquid.
46,47
Substrates coated with 3-aminopropyltriethoxy silane (APTES)
have been used to immobilize both Gram-negative and Gram-positive
bacteria,
and polycoated vinyl plastic has proven useful for immobilizing
bacterial spores such as
E. coli
in liquid.
31,48,49
In some cases, the interactions between the microbial cell and an
untreated substrate are strong enough to ensure immobilization. For
example, the actinomycete
B. atrophaeus
was imaged in liquid after
immobilization on freshly cleaved mica.
50
In bioilm research, simply growing
the cells on the imaging substrate has also been used to immobilize bacteria
for AFM imaging.
51-53
Increased time (hours to days) is generally required
to prepare a sample in this manner as the bacteria synthesize polymers to
condition the substrate to make it conducive for attachment and growth.
Whereas researchers studying bioilm characteristics may prefer the close
packing of cells in bioilms, others favour cells that are somewhat dispersed
on the substrate so that morphological distortions and constraints due to
tight packing are avoided.
For immobilization techniques that rely primarily on electrostatic
interactions between the microbe and the substrate, buffer salts need to be
evaluated. In some cases, the addition of divalent cations to the buffer can
facilitate binding.
54
Successful imaging in water has been reported, but one
must consider that water can create large, detrimental osmotic pressures on
some bacteria. Therefore, using an isotonic solution like 0.25 M sucrose is
advisable.
30,33,55
Because of these limitations, even stronger binding has been
sought. Alternatively, covalent bonding strategies have been used in which
substrates modiied with amino groups were subsequently cross-linked to cells
Streptomyces coelicolor
Search WWH ::
Custom Search