Biomedical Engineering Reference
In-Depth Information
found in a similar arrangement in the genome of a
Mycoplasma pulmonis
,a
gliding
Mycoplasma
that is closely related to
M. mobile
[6, 27, 28], but not in
any other species. The nonexistence of obvious orthologs in other than closely
related species may suggest variation in the structures of gliding machinery. It
may also suggest that the number of proteins involved in
Mycoplasma
gliding
is quite small compared to that of other bacterial motility systems such as
flagella and pili, possibly because a large number of proteins and interactions
would hamper evolutionary change in the components.
Figure 6.6.
Gene locus of
M. mobile
coding gliding proteins. Four proteins involved
in the gliding mechanism are coded tandemly on the genome. The typical role of
each protein is presented in the parentheses.
6.3.4 Where is the Machinery?
To localize the gliding machinery we attached a small bead to the surface of
the
Mycoplasma
and traced its movement during gliding [43]. The bead was
carried by the
Mycoplasma
, remaining bound to the same position on the cell,
which did not rotate on its axis. After prolonged culture, the heads of
M.
mobile
tend to elongate. When cultured for an additional 24 hours after cell
numbers have reached their maximum, some of the cells that were still gliding
had an elongated head. Their movement suggested that the head dragged the
remainder of the organism (here referred to as the “body”) and sometimes
the body became stuck to something on the glass and the head was stretched.
This suggests that the force for gliding is generated around the head.
Localization of the gliding machinery was achieved by immunofluorescence
microscopy with a procedure modified to fit to
Mycoplasmas
[42, 49, 27]. The
results from all antibodies against Gli123, Gli349, and Gli521 proteins showed
that the gliding machinery localizes at the base of the membrane protrusion
(see Figure 6.7). As the protrusion has already been called the “head”, we
