Biomedical Engineering Reference
In-Depth Information
However, there have been few studies focusing on the relationship between
gliding and pathogenicity; it is dicult to separate the effects of cytadherence
from those of gliding because no cytadherence-positive and gliding-negative
strains have been isolated. D. Krause's group at Georgia University con-
structed such a strain of
M. pneumoniae
, and examined the infection by the
strain in cultured cells that had differentiated into tracheal cells. The results
showed that gliding motility is essential to translocation of
Mycoplasmas
to
the cell surface after they attach to cilia tip [45, 46].
6.3 Studies on Mechanism of
M. mobile
Gliding
M. mobile
, isolated from lesions on the gills of freshwater fish, does not have
direct clinical or industrial importance. Therefore, only a few people were
working on it up to 1997, and knowledge of its genetic system remains scarce
even today. However, its remarkable gliding properties are attracting an in-
creasing number of researchers.
6.3.1 Gliding Mutants
To identify the molecules involved in the gliding mechanism, we isolated mu-
tants defective in gliding [47]. Generally, the colony morphology of microor-
ganisms depends on their moving activity [17]. Therefore, to isolate mutants
defective in gliding, we used a variety of agar concentrations in the culture
media.
M. mobile
formed a typical “fried-egg” shape colony in media con-
taining greater than 0.5% agar. However, the colony shape changed in media
containing less than 0.5% agar. Under such conditions, the colonies tended
to be composed of small clusters; in 0.1% agar, they were reduced to a stack
of small clusters. Presumably,
Mycoplasmas
occasionally glide on the filamen-
tous network of agar and form small blocks of colonies. We exposed
M. mobile
to ultraviolet irradiation and screened for nongliding mutants by examining
colony morphology in 0.1% agar. We obtained ten mutants with altered glid-
ing and binding characteristics. One group, which consisted of five strains,
did not bind to glass, and consequently did not glide. Many of their cells
had irregular shapes. All of these mutants had mutations in the open reading
frames (ORFs) of the very large proteins that have been shown to be involved
in the gliding mechanisms. Another group, consisting of four strains, had a
20% greater gliding speed and a shorter cell axis than that of the wild-type
strain. We have not identified the mutation points of this group, nor can we
explain why these gliding strains show a colony morphology similar to that of
nonmotile mutants. Perhaps, the colony morphology may also be related to
some chemotactic activity that has not yet been discovered.
