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J. Bacteriol., 11 1996, 6525-6538, Vol 178, No. 22
O Rauprich, M Matsushita, CJ Weijer, F Siegert, SE Esipov and JA Shapiro
Proteus mirabilis colonies exhibit striking geometric regularity. Basic
microbiological methods and imaging techniques were used to measure
periodic macroscopic events in swarm colony morphogenesis. We distinguished
three initial phases (lag phase, first swarming phase, and first
consolidation phase) followed by repeating cycles of subsequent swarming
plus consolidation phases. Each Proteus swarm colony terrace corresponds to
one swarming-plus-consolidation cycle. The duration of the lag phase was
dependent upon inoculation density in a way that indicated the operation of
both cooperative and inhibitory multicellular effects. On our standard
medium, the second and subsequent swarm phases displayed structure in the
form of internal waves visible with reflected and dark-field illumination.
These internal waves resulted from organization of the migrating bacteria
into successively thicker cohorts of swarmer cells. Bacterial growth and
motility were independently modified by altering the composition of the
growth medium. By varying the glucose concentration in the substrate, it
was possible to alter biomass production without greatly affecting the
kinetics of colony surface area expansion. By varying the agar
concentration in the substrate, initial bacterial biomass production was
unaffected but colony expansion dynamics were significantly altered. Higher
agar concentrations led to slower, shorter swarm phases and longer
consolidation phases. Thus, colony growth was restricted by higher agar
concentrations but the overall timing of the swarming-plus-consolidation
cycles remained constant. None of a variety of factors which had
significant effects on colony expansion altered terracing frequencies at 32
degrees C, but the length of the swarming-plus-consolidation cycle was
affected by temperature and medium enrichment. Some clinical isolates
displayed significant differences in terracing frequencies at 32 degrees C.
Our results defined a number of readily quantifiable parameters in swarm
colony development. The data showed no connection between nutrient
(glucose) depletion and the onset of different phases in swarm colony
morphogenesis. Several observations point to the operation of density-
dependent thresholds in controlling the transitions between distinct
phases.
Copyright © 1996, American Society for Microbiology
Periodic phenomena in Proteus mirabilis swarm colony development
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637-4931, USA.
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