Liquid holding increases mutation induction by formaldehyde and some other cross-linking agents in Escherichia coli K12.

The induction by some cross-linking agents of forward mutations leading to nalidixic acid resistance in Escherichia coli K12/343/113 was considerably enhanced when a 24-h period of liquid holding was interpolated between treatment and growth phase. Liquid holding increased the mutagenic effectiveness of nor-nitrogen mustard (NNM) 28-fold, of phosphoramide mustard (PAM) 10-fold, and of tris-ethyleneimino)-phosphineoxide (TEPA), tris(chloroethyl)amine (TCEA) and chloroacetaldehyde (CAA) 3-fold, over the complete concentration range. By contrast, the activities of cisplatin (CDDP), transplatin (TDDP) and chloracetamide-N-metholol (CAM) were slightly decreased after liquid holding. Liquid holding did not measurably influence the mutagenicity of formaldehyde at low concentrations, whereas at higher concentrations an 8-fold increase was observed. As opposed to the considerable activity in the Uvr+ strain, formaldehyde was found not to be mutagenically active in an E. coli strain carrying a deletion of the uvrB gene.