Mutagenic characteristics of formaldehyde on bacterial systems

The mutagenic characteristics of formaldehyde on bacteria were examined. All the tester strains of Escherichia coli deficient in DNA-repair enzymes tested in the present study were significantly more sensitive to the killing effect of formaldehyde than the corresponding wild-type strain. Among the E. coli B strains, H/r30R (wild-type) and Hs30R (uvrA) were mutable, whereas NG30 (recA) and O16 (polA) were not. There is no appreciable difference in mutation frequency of E. coli B between the wild-type and the uvrA strains in a dose range below 4 mM. However, the mutation frequency of the wild-type strain started to decrease in a higher concentration range, whereas that of the uvrA strain continued to increase linearly. This was confirmed with the E. coli B/r tester strains. The decrease in mutation frequency may be produced by prolongation of the lag period before entering the S-phase so as to give the cells a greater chance for DNA repair through the excision mechanism. In fact, it was evidenced that formaldehyde retarded to a remarkable extent the initiation of DNA synthesis of the cells at the higher dose range used for mutation assay. Some discrepancies found between the results obtained in this study and those previously reported by Nishioka (1973) were pointed out.