A study on the survival of wild-type, laboratory and recombinant strains of the baker yeast Saccharomyces cerevisiae under sterile and nonsterile conditions.

Laboratory strains of Saccharomyces cerevisiae transformed with an expression vector coding for the human coagulation protein FXIIIa (transglutaminase) under the control of a GAL promoter element have been constructed. Experiments were carried out to assess the potential biological risk of this genetically engineered microorganism. We analyzed the survival of this transgenic strain in comparison to the plasmid-free homologous strain and a wild-type isolate under various conditions. No differences could be detected in the survival rate under sterile or nonsterile conditions. In soil suspensions and waste water with limiting amounts of nutrients, the number of living yeast cells declined continuously over a period of several weeks. In the presence of nutrients, the autochtonic microflora overgrew the yeast and the yeast died rapidly. The results indicate, that the transgenic yeast strain behaves like wild-type strains and the plasmid-free laboratory strain and has no properties which would make it fitter under environmental conditions, which are inappropriate for baker yeast. The results presented in this paper indicate a rapid disappearance of the recombinant yeast strain under natural conditions.