Survival of genetically-engineered and wild-type strains of the yeast Saccharomyces cerevisiae under simulated environmental conditions: a contribution on risk assessment.

A genetically-engineered strain of Saccharomyces cerevisiae employed for the industrial production of the human coagulation Factor XIIIa (rhFXIIIa) was used for a survival study under simulated environmental conditions. The homologous strain devoid of the recombinant plasmid and the homologous strain bearing the 2 microns-based vector plasmid without the rhFXIIIa-encoding DNA insert were compared. The strains were introduced into natural soil/water suspension, into soil/medium suspension and into waste water. After intervals, samples of cell suspensions were taken and viable cell numbers were determined by plating on antibiotic-containing medium. In addition, a non-radioactive technique involving enhanced chemiluminescence was employed to detect plasmid-bearing yeast cells. The rhFXIIIa expression plasmid showed a high stability during the simulated environmental condition. No differences in survival rates, however, could be detected for the plasmid-bearing and plasmid-less strains under the three conditions tested, suggesting that the presence of plasmid does not confer selective advantages on the survival of the yeast cells. It is concluded that, even after accidental release of the engineered yeast cells into the environment, elimination rates would be comparable to those for non-recombinant yeast strains.