Increased Mutation Rate of E. coli K12λ Cultures Maintained in Continuous Logarithmic Growth

Continuous logarithmic growth of E. coli K12λ in an automatic culture cell resulted in marked increases in the proportion of several mutants. The P₁ phage-resistant cells increased 10 to 3000 times, the T₂ phage-resistant cells 1 to 1000 times, the neomycin-resistant cells 1 to 10 times, and the virus-producing cells 30 to 70 times. No change occurred in the penicillin-resistant cells. Calculation of the growth curves and direct determination of the mutation rates by the null fraction method showed that the increases in the proportion of mutants were due to increases in the mutation rates.