Common baker's yeast (Saccharomyces cerevisiae) is normally grown at 37°C, but it will grow actively at temperatures down to approximately 25°C. A haploid culture of wild-type yeast is mutagenized with EMS. Cells from the mutagenized culture are spread on a complete-medium plate and grown at 25°C. Six colonies (1 to 6) are selected from the original complete-medium plate and transferred to two fresh complete-medium plates. The new complete plates (shown) are grown at 25°C and 37°C. Four replica plates are made onto minimal medium or minimal plus adenine from the 25°C complete-medium plate. The new plates are grown at either 25°C or 37°C and the growth results are shown.

Which colonies are prototrophic and which are auxotrophic? What growth information is used to make these determinations? <>

Key Concepts

Prototrophy and Auxotrophy

Prototrophy refers to the ability of an organism to synthesize all essential compounds needed for growth from basic nutrients, while auxotrophy indicates a mutation that prevents the organism from synthesizing a specific compound, requiring it to be supplied in the growth medium. In yeast, prototrophic strains can grow on minimal media, whereas auxotrophic strains need additional nutrients, such as adenine, to thrive.

Mutagenesis

Mutagenesis is the process of inducing mutations in an organism's DNA, often using chemical agents like ethyl methanesulfonate (EMS). This technique is crucial for studying gene function and identifying mutations that affect growth characteristics, such as temperature sensitivity or nutrient requirements in yeast, which can lead to the classification of colonies as prototrophic or auxotrophic.

Temperature Sensitivity in Yeast

Temperature sensitivity in yeast refers to the organism's ability to grow at different temperatures, which can affect metabolic processes and gene expression. In this experiment, the growth of yeast colonies at 25°C and 37°C helps determine their nutritional requirements and whether they are prototrophic or auxotrophic, as some mutations may only manifest under specific temperature conditions.