This 1972 study by Hardy and Meynell investigated how mitomycin-C affects colicin production in Escherichia coli carrying various colicin factors. Colicins are bacterial toxins whose production can be induced by DNA-damaging agents. Previous work suggested only certain colicin factors responded to mitomycin-C treatment, but this study demonstrates that all nine colicin factors tested showed increased titres following mitomycin-C exposure, regardless of whether the factor was self-transmissible. The key difference from earlier conflicting results was methodological: previous studies used chloroform to kill cultures before titration, which ineffectively released cell-bound colicins of B, I, and V groups. The authors used ultrasonics to disrupt cells instead, providing more accurate measurement. Results showed increases in recA+ (recombination-proficient) bacterial hosts but minimal increases in recA mutant hosts, suggesting the bacterial recombination machinery is necessary for the effect. The authors cautiously note that mitomycin-C increases colicin titres without definitively establishing whether this results from increased synthesis, factor induction, or other mechanisms requiring further investigation.

Key findings

• Mitomycin-C increased titres of all nine colicin factors tested, regardless of whether they comprised sex factors
• The response to mitomycin-C required functional recA+ (recombination-proficient) hosts; recA mutant hosts showed minimal titre increases
• Improved methodology using ultrasonics rather than chloroform for cell lysis revealed that B, I, and V group colicins are predominantly cell-bound and require proper lysis techniques for accurate titration
• Previous conflicting results about which colicin factors respond to mitomycin-C likely resulted from technical differences in colicin measurement rather than biological differences