Genetic control of flocculation in Escherichia coli.

Escherichia coli cells form flocs or aggregates by overproducing type 1 pili. When the pil operon is placed under the control of a tac or lac promoter-operator sequence, the bacterial cells can be induced to form flocs by adding isopropyl-beta-D-thiogalactopyranoside to the culture medium. This phenomenon of genetically induced flocculation can aid in the downstream of biological products. This paper describes the construction of two artificially controlled plasmids which cause cell flocculation. Cell aggregates 50 microns in mean diameter were obtained 1 h after the cells were induced.