Characterization of rpo-B mutant of a strain of Escherichia coli to confirm its suitability for routine work related to recombinant DNA technology

Rifampicin resistant spontaneous mutant of a popular laboratory strain of Escherichia coli (DH5 alpha) was isolated and found to resist high level of the drug in growth medium. The growth of the isolate was found to be slower than its wild-type counterpart. Its ability to get transformed into drug-resistant state through transformation by chemical means as tested using plasmid DNA from three different size categories, was found to be at par with the wild type. Other properties, viz., alpha-complementation and ability to express foreign gene remained unaltered. The utility of the rifampicin-resistant phenotype as a potential chromosomal genetic marker was demonstrated in a typical conjugation experiment to establish the ability of the mutant to act as recipient strain for a recombinant, mobilizable plasmid DNA molecule with the advantage of drug-mediated, high efficiency selection. Substitution of the wild strain with the mutant for routine experimentations related to recombinant DNA technology was concluded to be appropriate and of advantage.