Determining survival fractions of Saccharomyces cerevisiae in response to ionizing radiation in liquid culture

Saccharomyces cerevisiae survival fractions (SFs) in response to X-ray radiation were determined by two new methods: an OD(600)-based method and a 96-well method. For the OD(600)-based method, cells were exposed to various X-ray doses and inoculated into fresh medium: a lower biomass accumulated, indicating fewer surviving cells within the investigated dose range (0–100 Gy). For the 96-well method, diluent containing ~0–100 cells was equally divided into 96 droplets and respectively inoculated into 96 wells containing 200 μl of broth: fewer wells without S. cerevisiae clones indicated more surviving cells after 48 h of incubation. Corresponding quantitative systems were established. Both methods were sensitive and reliable. The OD(600)-based method is simple and fast, and the 96-well method simplifies the counting process. SF estimates by the OD(600)-based method were lower than those by 96-well methods owing to cell cycle arrest. In addition, comparisons of newly proposed and plate-counting methods indicated a higher rate of repair in S. cerevisiae in liquid culture than on agar.