Discovery of Degenerate Genetic Code (question)

[Genetictac]

Hello to all,

I am a student in Master1 of cellular and molecular biology. While looking for how the genetic code was discovered (and especially the notion of degeneracy), I came across a historical article from 1961 (General Nature of Genetic Code for Proteins, Crick et al.). I am trying to understand how the T4 rII system used in the experimental model in the article works. I found a good video in English explaining this but I am not sure I understand the difference between K and B cultures very well. Could someone please enlighten me? Here is the link to the video: https://youtu.be/4PwprU2KYoM

Have a nice day,

Jérome (from France) 😀