Biological effects of dyes on bacteria. VI. Mutation induction by acridine orange and methylene blue in the dark with special reference to Escherichia coli WP6 (polA1).
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study on bacterial strains (bench research).
PubMed 6379434 · doi:10.1016/0165-1218(84)90105-8
What was done
Researchers evaluated the mutagenic effects of acridine orange (AO) and methylene blue (MB) in the dark on wild-type (WP2) and repair-deficient strains of Escherichia coli B/r, specifically the DNA polymerase I-deficient strain WP6 (polA1). Mutagenesis was measured by the induction of resistance to T5 bacteriophage.
What was found
In wild-type strain WP2, AO did not induce mutations in the dark; the presence of 2 microM AO reduced the spontaneous mutation rate by 41%, from 4.1 to 2.4 mutants/10(8) cells/generation. In the polymerase I-deficient strain WP6 (polA1), 2 microM AO increased the mutation rate in the dark 14-fold. MB showed weak to moderate mutagenicity in strain WP6 and other repair-deficient strains tested, though specific quantitative rates for MB were not reported in the abstract.
Why it matters
These findings suggest that functional DNA polymerase I protects against frameshift mutagenesis caused by intercalated compounds in the dark, indicating that dye-induced mutations likely occur at the semiconservative DNA replication fork.
Limits
The study is restricted to in vitro bacterial models and does not provide direct evidence for eukaryotic or human toxicity. Specific quantitative mutation counts, replicate numbers, and statistical confidence intervals for methylene blue and other repair-deficient strains are absent from the abstract.
Cited by
- supports Methylene blue can intercalate into DNA and possibly cause mutations.