Control of Sporulation in Fused Protoplasts of Bacillus subtilis 168

Complementable spo mutants of Bacillus subtilis could be ‘rescued’ to form heat-resistant spores by fusing them with sporulating cells of the wild-type strain ( Dancer & Mandelstam, 1981 ). The latter strain acted as a ‘rescuer’. Rescuer protoplasts had to be derived from cells grown in a medium that allowed rapid and synchronous sporulation subsequently. Even protoplasts made from vegetative cells growing in such a medium (t 0 protoplasts) acted as rescuers. Therefore, it was not necessary for the rescuer cells to have initiated sporulation before they were converted to protoplasts.

The genetic requirement for t 0 rescuer protoplasts was that they were spo + for the gene to be complemented. Strains in the same complementation group did not rescue one another. Protoplasts of spo strains blocked at stages O, IV and V of sporulation acted equally well as rescuers whether they were converted to protoplasts at t 0 or t 3 (i.e. 3 h after transfer to sporulation medium). However, t 3 protoplasts of stage II and stage III mutants were much less effective rescuers than their t 0 counterparts. This difference was not due to a dominance effect expressed only in t 3 protoplasts.