The role of nutrient broth supplementation in UV mutagenesis of E. coli

Postirradiation expression of UV-induced reversion is examined to understand the different yields of E. coli revertants on agar media unsupplemented, supplemented with a small amount of the required amino acid, or supplemented with nutrient broth. Protein synthesis is determined in irradiated cells incubating on these three media by observing the incorporation of [³H]proline. Nutrient broth supplementation is known to yield a large number of suppresor-containing revertants which does not develop with supplementation of a small amount of the required amino acid. However, the rates of protein synthesis in cells on these two media are found to be similar. Consequently the rate of protein synthesis per se does not seem responsible for enhance expression of suppressor-containing revertants. An empirical model is proposed to realte nutrient broth enhancement to mutation frequency decline and finalization of GC to AT transitions.