Abstract: The subject of the present invention is a selection system for microorganisms, which is based on the inactivation of an essential translocating enzyme and the curing of this inactivation by means of an indentically acting factor which is made available to the cells concerned by means of a vector. One important area of application for this system is includes processses for protein production by culturing cells of a microorganism strain that are characterized by this selection system, particularly such that the transgene of interest is located on the same vector performing the cure. Appropriate microorganisms, possible uses for genes of translocation enzymes and vectors are likewise presented, including in particular the use of the gene secA from gram-negative or gram-positive bacteria such as B. licheniformis.