Structure and replication of chromosomes in competent cells of Bacillus subtilis.

Competent cultures of Bacillus subtilis 168 were fractionated on gradients of Renografin-76 to obtain a population enriched for competent cells. The cells in this fraction contained two nuclear bodies. The competent cell fraction synthesized deoxyribonucleic acid and ribonucleic acid at reduced rates compared to the noncompetent cell fraction and appeared to divide synchronously upon incubation. The state of the chromosome in competent cells was determined by density transfer experiments and marker frequency analyses. The results are consistent with a competent cell possessing two, or a multiple of two, chromosomes, one complete and the other partially duplicated. During subsequent growth the partially completed chromosome replicates preferentially.