Biochemical differentiation in large colonies of Enterobacter cloacae

Large colonies of Enterobacter cloacae which were about 700 micrometer thick were frozen in liquid nitrogen and sectioned horizontally. The sections were disrupted and several oxidative enzymes were assayed in the crude unfractionated homogenates. In the top 120 micrometer of the colonies the specific activities of the enzymes were high and characteristic of aerobically adapted cells. Cells nearer the base of colonies had very low enzyme activities.