Super optimal broth (SOB) broth is used for the preparation of nutritionally-rich growth medium and transformation of competent E. coli.

SOB broth growth medium is nutritionally rich, containing casein hydrolysate and yeast extract as sources of nitrogenous compounds and growth factors, plus magnesium sulphate as a supply of magnesium ions necessary for DNA replication.

When dissolved at 25,5 g/L of water, yields tryptone (20 g/L), yeast extract (five g/L), sodium chloride (0,5 g/L).

Store SOB broth powder at room temperature (18 to 26 °C). Store prepared medium cold (2 to 8 °C).