Mutagenesis, Vol. 14, No. 1, 95-102,
January 1999
© 1999 UK Environmental Mutagen Society/Oxford University Press
Hydrogen peroxide and coffee induce G:C
T:A transversions in the lacI gene of catalase-defective Escherichia coli
Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, Avenida de Medina Azahara s/n, 14071-Córdoba, España
The mutagenicity of hydrogen peroxide (H2O2) was compared with that of coffee, a complex mixture which generates H2O2. An Escherichia coli strain defective in catalase activity (katG katE double mutant) and carrying a single copy mucAB (pRW144) plasmid was constructed to enhance the mutagenic response to oxidants. The ability of the mucAB genes to influence the type, frequency and distribution of H2O2-induced mutations was also investigated in isogenic bacteria lacking pRW144. Induced mutational spectra were characterized and compared with that of spontaneous mutagenesis. A total of 444 independent forward mutations affecting the first 210 bp of the lacI gene were identified by DNA sequence analysis. The spontaneous mutation spectrum showed no bias (P = 0.52) for substitutions at G:C base pairs. In contrast, in the H2O2-induced spectrum substitutions occurred preferentially at G:C base pairs (P < 0.0001) with a preponderance of G:C
T:A transversions (43.4% of H2O2-induced mutants versus 17.3% of spontaneous mutants). These data support the view that 7,8-dihydro-8-oxoguanine is the main premutagenic lesion induced by H2O2 and that catalase-defective bacteria have elevated levels of 8-oxoguanine in chromosome DNA after H2O2 exposure. Coffee produced a similar distribution of mutational events as H2O2 (P > 0.05), suggesting that this compound may be the main cause of the coffee-induced mutagenesis. The presence of plasmid pRW144 did not affect the frequency of H2O2-induced G:CT:A transversions, but caused an increase in A:TT:A transversions and a decrease in –1 base frameshifts. Although the frequencies of G:CT:A transversions were similar in all three induced spectra (H2O2 and coffee ± pRW144), differences were observed in location of mutations throughout the target gene.
1 To whom correspondence should be addressed. Tel: +34 957 218695; Fax: +34 957 218688; Email: bb1pucuc{at}uco.es
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