Method for immobilizing living microorganisms and method for preparing living microorganisms

To provide a new means of immobilizing single cells or small groups of microorganisms in a viable condition on the surface of a substrate, and to provide a means of detaching in a viable condition the microorganisms that have been immobilized using this new means. A method for immobilizing living microorganisms, comprising a step (1) of disposing a solution containing microorganisms as an electrolyte on the surface of a substrate at least one portion of which is an electrode, and applying a constant potential to the electrode to cause at least a portion of the microorganisms to attach to the surface of the substrate. The constant potential in step (1) is greater than -0.5 V but not greater than -0.2 V (vs Ag/AgCl) or greater than +0.2 V but not greater than +0.4 V (vs Ag/AgCl). The electrolyte in step (1) does not contain a source of nutrition for the microorganisms. A method for preparing living microorganisms, comprising step (1) and a step (2) of applying a high-frequency wave potential to the electrode to detach in a viable condition the microorganisms that have attached to the surface of the substrate. The high-frequency wave potential in step (2) has a frequency falling within a range of 1 KHz to 10 MHz and has a potential range of ± 1.0 V (vs Ag/AgCl) or narrower, preferably± 0.1 V (vs Ag/AgCl) or narrower. The electrolyte of step (2) has a salt concentration of 10 g/L or lower.