Final answer:
Replica plating is a biological technique used to identify bacterial mutants, such as those unable to synthesize specific nutrients (auxotrophs) or those resistant to antibiotics. It involves transferring colonies from a nutritionally complete medium to selective media to observe their growth patterns.
Step-by-step explanation:
Replica plating is a technique used to identify bacterial mutants, such as auxotrophs. Auxotrophs are mutants with a deficiency in the biosynthesis pathways of certain nutrients, making them unable to grow on media that lack these specific nutrients. To find a mutant, scientists first expose bacteria to a mutagen and then plate these cells on a nutritionally complete medium to allow for colony formation. They then use a sterile piece of velvet to transfer cells from these colonies to various media plates with and without specific nutrients. The growth patterns on these plates identify auxotrophic mutants. Furthermore, replica plating can also be used to identify bacterial colonies that are resistant to antibiotics.
Cells from the master nutritionally complete plate are plated onto various selective media, including ones with antibiotics e.g., an ampicillin agar plate. After colonies grow, researchers create a replica plate by laying a filter over the master plate to pick up cells from each colony. This replica is then placed onto a new agar plate containing a different antibiotic, such as streptomycin. Only colonies that are resistant to the second antibiotic will grow on the replica filter. The presence of these resistant colonies indicates that the bacterial cells carry the plasmids or genetic mutations that confer resistance to the antibiotics.