Mutagenicity of cigarette smoke condensate in Neurospora crassa

The mutagenicity of cigarette smoke condensate (CSC) was investigated in Neurospora crassa in the presence and absence of S9 mix prepared from Aroclor-1254-induced rat liver. CSC from the University of Kentucky Reference Cigarette 1R1 was assayed in a forward-mutation test at the adenine-3 (ad-3) region in resting conidia of 2-component heterokaryons. In the absence of S9 mix, CSC exhibited direct-acting mutagenicity. CSC was also mutagenic in the presence of S9 mix, but higher doses were required than in the absence of S9 mix. The dose range, survival curves, and mutation-induction curves were not significantly different when CSC was used in the presence of unheated or heat-inactivated S9. There was a positive association between killing and mutagenicity, and CSC killed conidia of N. crassa by a cytoplasmic, rather than by a nuclear, mechanism. The mutagenic potency of CSC was similar in a repair-sufficient and a nucleotide excision repair-deficient heterokaryon of N. crassa. CSC did not exhibit a photodynamic effect for killing, and CSC caused more killing at high pH than at low pH. In addition, CSC caused more killing at 37 degrees C than at 25 degrees C and also caused more killing in higher concentrations (20%) of solvent (DMSO) than in low concentrations (1%). This is the first report of the presence of potent direct-acting mutagens in CSC.