Obtaining of silver-resistant Saccharomyces cerevisiae by evolutionary engineering

Silver is a non-essential metal and it is used in the medical applications, but it is highly toxic for the biological systems. In the environment and industrial processes, yeast cells can expose to silver stress. Evolutionary engineering, as an inverse metabolic engineering approach, has been used for the obtaining of desired phenotypes in the yeast. To better understand of silver tolerance and to obtain silver-resistant yeast strain, here, we used evolutionary engineering method to obtain silver-resistant Saccharomyces cerevisiae. For this aim, firstly, genetic diversity of S. cerevisiae was randomly increased by ethyl methane sulfonate (EMS) mutagenesis, and then the initial mutant population was exposed to silver stress under gradually increasing levels to select fitter mutants. After the selection procedure, individual mutants were randomly picked up from the last population, stress resistance of the each mutant was investigated, and silver-resistant mutants were successfully isolated. Cross-resistance analysis results indicated that silver resistance could have similar molecular patterns related with copper tolerance and oxidative stress resistance. Growth physiological analysis also revealed that silver-resistant mutant can overcome silver stress better than the wild type. Microarray analysis showed that the mutant had a slower growth compared to wild-type by the down-regulation of ribosomal genes and a better viability under silver-stress conditions by up-regulating genes on copper-stress, oxidative-stress, and DNA damage response. In conclusion, the obtained silver-resistant mutant S. cerevisiae can be used for understanding of silver tolerance mechanism in the cell, and it might have potential usage in the industrial or silver nanoparticle applications.