Links & Resources
>Other Web Sites
>E-Mail Directory
>Myxo References
>Events
Last update
Development (2.1 MB). Download a QuickTime movie showing fruiting body development (1200x time-lapse).
In the interior of this structure, rod-shaped cells differentiate into spherical, thick-walled spores. Biochemical changes, such as the synthesis of new proteins and alterations in the cell wall, occur in parallel to the morphological changes. Several intercellular signals required during the process of development have been identified and given names like A signal, B signal and C signal. These signals play a role in triggering expression of several genes involved in development (Kroos and Kaiser, 1987). Identification of these developmentally-expressed genes has been facilitated by the use of Tn5-lac transposon mutagenesis.
During
the aggregation of M. xanthus cells into fruiting bodies, dense
ridges of cells appear to move in traveling waves called ripples.
Both fruiting body development and rippling are observed in various myxobacterial
species. Ripples wax and wane over a 5 hour period during the developmental
process, but are not a requirement for fruiting body development. Further
study of rippling should shed light on how swarms of myxobacteria coordinate
their movement. Pictured at right is a field of immature fruiting bodies
with ripples formed by cells outside of the aggregates (Shimkets
and Kaiser, 1982, J Bacteriol 152:451-61).
Rippling
(1.7 MB). Download a QuickTime movie showing ripples in action (150x speed,
12 frames/sec).
Coordinated cell motility, or swarming, also occurs during vegetative growth. This "wolf-pack" behavior facilitates predatory feeding by increasing the extracellular concentration of digestive enzymes secreted by the bacteria. M. xanthus moves across surfaces by means of a poorly understood mechanism known as gliding motility. Gliding is controlled by two distinct genetic systems: the adventurous (A) and social (S) motility systems (Hodgkin and Kaiser, 1979ab). S-motility is activated when cells are in proximity to each other, while A-motility allows cells to move independently. Mutations in the S-system genes do not interfere with A-motility, and vice-versa; a single mutation in the mgl locus, however, interferes with both types of swarming.
Pictured below are the edges of colonies of M. xanthus grown on agar. The top frame shows the smooth edge of a colony which has neither A nor S motility, and therefore does not swarm at all; this is characteristic of strains with a single mutation in the mgl locus, as well as of strains with one mutation in each of the two motility systems. The left frame depicts a colony in which only A-motility is active; the right frame shows a colony in which only S-motility is active. Finally, the bottom frame shows a wild-type colony in which both A and S-motility are active.
| Adventurous
motility (1.2 MB). Download a QuickTime movie of the
edge of a colony displaying adventurous motility (600x time-lapse, 10 frames/sec). |
Social
motility (410 K). Download a QuickTime movie of the edge
of a colony displaying social motility (1500x time-lapse, 10 frames/sec). |