Comparison of SYBR Green I nucleic acid gel stain mutagenicity and ethidium bromide mutagenicity in the Salmonella/mammalian microsome reverse mutation assay (Ames test)

SYBR Green I nucleic acid gel stain is an unsymmetrical cyanine dye developed for sensitive detection of nucleic acids in electrophoretic gels. Its mechanism of nucleic acid binding is not known, whereas the most commonly used nucleic acid gel stain, ethidium bromide, is a well-characterized intercalator. We compared the mutagenicity of SYBR Green I stain with that of ethidium bromide in Salmonella/mammalian microsome reverse mutation assays (Ames tests). As expected J. McCann, E. Choi, E. Yamasaki, B.N. Ames, Proc. Natl. Acad. Sci. USA, 72 (1975) 5135-5139], ethidium bromide showed high revertant frequencies in several frameshift indicator strains (averaging 68-fold higher than vehicle controls in TA98, 80-fold higher in TA1538, 15-fold higher in TA1537, and 4.4-fold higher in TA97a), only in the presence of rat liver extracts (S9). Small increases in revertant frequencies were observed for ethidium bromide in the base-substitution indicator strain TA102 both in the presence and absence of S9 (averaging 2.0- and 1.8-fold higher than vehicle controls, respectively) and in base-substitution indicator strain TA100 in the presence of S9 (averaging 1.6-fold higher than vehicle controls). A small mutagenic effect was detected for SYBR Green I stain in frameshift indicator strain TA98 (averaging 2. 2-fold higher than vehicle controls) only in the absence of S9 and in base-substitution indicator strain TA102, both in the presence and absence of S9 (averaging 2.2- and 2.7-fold higher than vehicle controls, respectively). Thus, SYBR Green I stain is a weak mutagen and appears to be much less mutagenic than ethidium bromide. These results suggest that SYBR Green I stain may not intercalate, and if it does, that its presence does not give rise to point mutations at a high frequency.