Fusion of bacterial protoplasts.

Abstract

Prototrophic Bacillus subtilis cells can be formed in the presence of DNase as a result of cell fusion occurring in mixed populations of protoplasts derived from 2 parental strains which are both nutritionally-complementing and polyauxotrophic. No prototrophs ever appear from mixed nonprotoplasted bacteria or from the auxotrophic parental protoplasts plated separately. The frequency of prototroph formation, which is appreciable only when the mixed protoplasts are exposed to polyethylene glycol treatment, may exceed 1 .times. 10-4 of the total protoplast population initially present, which is 1 to 4 .times. 10-3 of those protoplasts which reverted to the bacillary form. It is strongly dependent on the number and chromosomal location of the markers used in the selection of the prototrophs and it is unaffected when either 1 of the parental strains bears the phage .vphi.105 in the inducible prophage state. No auxotrophic bacteria, parental or otherwise, were found as segregants from repeatedly isolated prototrophic clones growing in a nonselective medium. Unselected markers segregate among the selected recombinants. The observed formation of prototrophic bacteria is apparently due to protoplast fusion, a process which does not induce prophage development, and the only stable products of the resulting diploid state may be haploid recombinants.