Biomedical Engineering Reference
In-Depth Information
Figure 6.4.
Electron micrograph of negatively stained
M. pneumoniae
. The attach-
ment organelle of a cell is pointed by an arrow.
does not show any obvious chemotaxis [4, 32, 5]. Granted, this failure to
detect chemotaxis may be caused by the experimental conditions, because
the environments of
Mycoplasmas
in nature are distinct from those of other
motile bacteria, which may be reflected to the remarkable reduction of genome
sizes in
Mycoplasma
species [1]. Thus, we cannot rule out the possibility
of chemotaxis in
Mycoplasmas
. Still, if they have chemotaxis, it is caused
by a novel mechanism different from that of other bacteria, just as gliding
motility in
Mycoplasmas
must be caused by different mechanisms because
no homologs of two-component system genes can be found in their genomes
[33, 34, 35, 6, 36, 37]. Furthermore, the physical conditions of
Mycoplasmas
in
their hosts require motion for the sake of motion; even random movements are
sucient. Generally, gliding
Mycoplasmas
bind to animal tissues tightly and
cluster. If they stay in the same position without movement, they will use up
the nutrients and pollute their environment with their wastes. Random move-
ments will enable them to get better conditions for propagation. In the case of
M. mobile
, the cells show rheotaxis, by which the organism moves upstream
of liquid flow as usually observed in fish [38].
M. mobile
responds to a flow of
100
−
300
μ
m
/
s with a time lag of 1-3 s and exhibits a change of direction and
