Caveat Mutator

The use of whole genome microarrays for monitoring mutagenised or otherwise engineered genetic derivatives is a potentially powerful tool for checking genomic integrity. Using comparative genomic hybridization of a number of unrelated, directed deletion mutants in Escherichia coli K-12 MG1655 we identified unintended secondary genomic deletions in the flhDC region in deltafnr, deltacrp, and deltacreB mutants. These deletions were confirmed by PCR and phenotypic tests. Our findings show that non-motile progeny are found in some populations of MG1655 directed deletion mutants, and studies on the effects of gene knock-outs should be viewed with caution when the mutants have not been screened for the presence of secondary deletions, or confirmed by other methods. Keywords: comparative genomic hybridisation We used the CGH method to genetically characterize a series of regulatory gene deletion mutants we had made in MG1655 using the lamda-Red method of Datsenko and Wanner. A number of strains were tested using CGH, and each strain was tested only once. Genomic DNA isolated from wt MG1655 was used as a reference in all hybridisations.