appendix a 
2 
have established that the chromosome is circular (4) and replicates 
bidirectionally (5). 
Transformation with purified fragments of DNA is a highly efficient 
process in B_. subtil is with frequencies of 1 to 4% usually attained for 
any auxotrophic or antibiotic resistance markers. Frequencies of approxi- 
mately 10% transformation can be achieved with DNA prepared from gently 
lysed L-forms or protoplasts (6). These large fragments of DNA are readily 
incorporated by the recipient cell. Generalized transduction occurs with 
bacteriophages SP10 (7), PBS1 (8), and SPP1 (9), while a low frequency of 
specialized transduction has been reported with bacteriophage <f>105 (10). 
Although transformation is most efficient in homologous crosses (B. 
subtil is into B_. subtil is ) , it has also been possible to exchange DNA 
among closely related species (11). The most extensively studied members 
of the B_. subtil is genospecies include B_. 1 icheniformis , B_. pumi lus , B_. 
amylol iquefaciens , and B_. globigi i (refer to reference 12 for a review 
and references 13-15 for examples of this heterologous exchange). This 
exchange occurs even though there is a surprisingly wide discrepancy 
between DNA - DNA hybridization among these organisms (16). Even though 
the frequency of transformation is low in the heterologous cross [e.g., B_. 
amylol iquefaciens (donor)/B_ subtil is (recipient)], the newly acquired DNA 
from B_. amylol iquefaciens in the B_. subti 1 i s background can be readily 
transferred at high efficiencies to other recipient strains of B_. subti 1 is 
(14). Therefore, the extremely high frequency of transformation permits 
the recognition and selection of rare events. 
[ 122 ] 
