Properties of Bacillus subtilis 168 derivatives freed of their natural prophages.

An isogenic set of Bacillus subtilis 168 strains which are non-inducible for prophage PBSX and are cured of prophage SP beta has been constructed. By utilizing these strains, prophage SP beta has been shown to control the inducible DNA modification system which exists in this bacterium. However, neither the PBSX nor the SP beta prophages alter the ability of the bacterium to undergo genetic recombination, to repair damaged DNA or to sporulate. Prophageless B. subtilis would be a useful host for the phi 3T cloning vector, because of the absence of vector--prophage interactions.