Multicellular Behavior of Bacteria and Dynamics of Their Colony Formation

We have studied the，growth mechanism and morphological change，in colony formation of bacteria from the viewpoint of physics of pattern formation。The colony differs in size，form，and color according to bacterial species.It also changes its form sensitively with the variation of environmental conditions.This implies that although usual bacteria such as Escherichia coli are regarded as single cell organisms，they never make，their colony independently and randomly but somehow collaborate multicellularly.We have thus tried to extract some simple，and universal behaviors in growth from such complex bacterial systems.Here we varied only two parameters to investigate the colony growth；concentrations of nutrient C I D2n ii D2 and agar C I D2a ii D2 in a thin agar plate as the incubation medium。Other parameters specifying experimental conditions such as temperature were kept constant.We mainly used a typical bacterial species Bacillus subtilis。Otherwise the experimental procedures are standard.It was found that coloniels show characteristic patterns in the specific regions of values of C I D2n文件D2 and C I D2a文件D2 in the morphological diagram and the patterns change drastically from one region to another.They were classified into five types；fractal DLA-like，compact Eden-like，concentric ring-like，simple disk-like and densely branched DBM-like。We have experimentally elaborated characteristic properties for each of these colony patterns.We have also done the same experiments for a bacterial species Proteus mirabilis.This species has been well-known for more than a century to form macroscopically almost perfect concentric-ring like，colonies with approximately equal spacings on the surface of semi-solid substrate such as an agar plate。We have elucidated macroscopic and phenomenological mechanism for the repeated interface growth of the concentric-ring like colonies.

We have studied the, growth mechanism and morphological change, in colony formation of bacteria from the viewpoint of physics of pattern formation. The colony differs in size, form, and color according to bacterial species. It also changes its form sensitively with the variation of environmental conditions. This implies that although usual bacteria such as Escherichia coli are regarded as single cell organisms, they never make, their colony independently and randomly but somehow collaborate multicellularly. We have thus tried to extract some simple, and universal behaviors in growth from such complex bacterial systems.Here we varied only two parameters to investigate the colony growth; concentrations of nutrient CィイD2nィエD2 and agar CィイD2aィエD2 in a thin agar plate as the incubation medium. Other parameters specifying experimental conditions such as temperature were kept constant. We mainly used a typical bacterial species Bacillus subtilis. Otherwise the experimental procedures are standard. It was found that coloniels show characteristic patterns in the specific regions of values of CィイD2nィエD2 and CィイD2aィエD2 in the morphological diagram and the patterns change drastically from one region to another. They were classified into five types; fractal DLA-like, compact Eden-like, concentric ring-like, simple disk-like and densely branched DBM-like. We have experimentally elaborated characteristic properties for each of these colony patterns.We have also done the same experiments for a bacterial species Proteus mirabilis. This species has been well-known for more than a century to form macroscopically almost perfect concentric-ring like, colonies with approximately equal spacings on the surface of semi-solid substrate such as an agar plate. We have elucidated macroscopic and phenomenological mechanism for the repeated interface growth of the concentric-ring like colonies.