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Agar 2026-10-18
Lederberg replica plating experiment 2026-10-18
Joshua Lederberg and Esther Lederberg reported replica plating in 1952. They autoclave-sterilized velveteen and secured it pile-up on a wood or cork cylinder with a metal hoop. Inverted agar plates touched the fabric lightly. Pencil marks or pin indentations fixed orientation. Complete-medium and minimal-medium replicas compared growth of biological colonies.[ref]
Replica plating and indirect selection of bacterial mutants by Joshua Lederberg and Esther Lederberg. pp. 399–402, Methods: Replica plating; Figure 1 caption; Results: plate orientation
Escherichia coli W-1 grew on plain agar; serial T-1 bacteriophage replicas showed resistant biological colonies at matching sites. Corresponding unexposed master regions seeded repeated broth-and-plain-agar enrichment, yielding resistant isolates. Stray-bacteriophage checks were negative; resistance persisted without challenge. This supported preexisting heritable resistance. The authors noted variable transfer and moisture-dependent resolution.[ref]
Replica plating and indirect selection of bacterial mutants by Joshua Lederberg and Esther Lederberg. pp. 401–403: transfer variability, Clonal occurrence of phage resistant mutants, Indirect selection and stray-phage checks; p. 404, Discussion
The Luria-Delbrück experiment uses variation between independently grown cell cultures to investigate the timing of resistant mutations. The Lederberg replica plating experiment adds a spatial route to a recoverable source: the tested samples identify an unexposed lineage. These are complementary arguments about mutation and natural selection. Growth readouts establish a tested phenotype; identifying the responsible nucleotide sequence requires other evidence, such as DNA sequencing.