cis-Platinum(II)diamminodichloride-induced mutagenesis in E. coli K12: crowding depression of mutagenesis

Cis-Platinum(II)diamminodichloride (cis-PDD)-induced mutations to prototrophy were studied in Escherichia coli. Mutagenesis was not detected in a recA nor in a lexA mutant, but was greater in a uvrA strain than in a repair-proficient strain, at a given treatment of cis-PDD. Increasing the plating density above 10(5) cells per plate did not give an equivalent increase in revertants per plate [crowding depression of mutagenesis (Bockrath et al., 1980)]. Growth rates were similar at different plating densities and crowding depression of mutagenesis was observed in both excision-proficient and excision-deficient strains. A filtrate of a plate wash from crowded plates, of either treated or untreated cultures, further reduced the mutation frequencies over that due to crowding depression of mutagenesis.