PERIODIC PHENOMENA IN PROTEUS-MIRABILIS SWARM COLONY DEVELOPMENT

Proteus mirabilis colonies exhibit striking geometric regularity, Basi c microbiological methods and imaging techniques were used to measure periodic macroscopic events in swarm colony morphogenesis. We distingu ished three initial phases (lag phase! first swarming phase, and first consolidation phase) followed by repeating cycles of subsequent swarm ing plus consolidation phases, Each Proteus swarm colony terrace corre sponds to one swarming-plus-consolidation cycle. The duration of the l ag phase was dependent upon inoculation density in a way that indicate d the operation of both cooperative and inhibitory multicellular effec ts, On our standard medium, the second and subsequent swarm phases dis played structure in the form of internal waves visible with reflected and dark-field illumination, These internal waves resulted from organi zation of the migrating bacteria into successively thicker cohorts of swarmer cells, Bacterial growth and motility were independently modifi ed by altering the composition of the growth medium. By varying the gl ucose concentration in the substrate, it was possible to alter biomass production without greatly affecting the kinetics of colony surface a rea expansion, By varying the agar concentration in the substrate, ini tial bacterial biomass production,vas unaffected but colony expansion dynamics were significantly altered, Higher agar concentrations led to slower, shorter swarm phases and longer consolidation phases, Thus, c olony growth was restricted by higher agar concentrations but the over all 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 leng th of the swarming-plus-consolidation cycle was affected by temperatur e and medium enrichment, Some clinical isolates displayed significant differences in terracing frequencies at 32 degrees C, Our results defi ned a number of readily quantifiable parameters in swarm colony develo pment. The data showed no connection between nutrient (glucose) deplet ion and the onset of different phases in swarm colony morphogenesis. S everal observations point to the operation of density-dependent thresh olds in controlling the transitions between distinct phases.