Final answer:
Replica plating is used to isolate auxotrophic bacterial mutants that cannot synthesize certain nutrients due to genetic mutations. It is done by transferring colonies onto different media to track their growth and identify mutants.
Step-by-step explanation:
What is Replica Plating Used to Isolate?
Replica plating is a microbiological technique used to isolate and identify bacterial mutants, particularly nutritional mutants known as auxotrophs. This method allows researchers to detect cells that cannot synthesize certain necessary nutrients due to mutations. In replica plating, a master plate with a nutritionally complete medium is first inoculated with mutagenized cells to grow colonies. Once grown, these colonies are transferred onto minimal media plates lacking specific nutrients, as well as another nutritionally complete plate, using a sterile velvet cloth to maintain the same spatial pattern. Cells that fail to grow on the minimal media but grow on the complete media indicate potential auxotrophic mutants. Through this comparative growth analysis, scientists can identify and further study these mutants.
Subsequently, replica plating can also apply to genomic libraries. Filters carrying phage or bacterial colonies are hybridized with specific probes to identify clones containing DNA sequences of interest. However, this process often involves screening for streptomycin-resistant colonies using replica filters of colonies grown on an ampicillin agar plate, where those colonies not growing on a streptomycin-containing plate are likely to possess recombinant plasmids.