Cell Division across the Volume of Colonies of Flavobacterium sp. 22

Six-day-old colonies ofFlavobacterium sp. 22 were studied by electron microscopy. Direct evidence was obtained of bacterial cell division across the entire colony volume, indicating that the colony growth ofFlavobacterium sp. 22 is not purely peripheral. It is argued that the colony shape is determined not only by peripheral growth but also by physical forces acting upon a droplet of liquid on the surface. For bacterial colonies developing on solid nutrient media, the intercellular matrix plays the role of such a liquid.