34 
exchanges genetic information with the host-vector or not, and the con- 
tainment conditions given for these two classes with E_. col i K-12 
host-vectors applied. Transfer of recombinant DNA to plant pathogens 
can be made safer by using nonreverting, doubly auxotrophic, non- 
pathogenic variants. Experiments using a plant pathogen that affects 
elements of a local flora will require more stringent containment 
than if carried out in areas where they are not common. 
Experiments with DNAs from eukaryotes (ant their plasmids or 
viruses) can also follow the criteria for the corresponding experi- 
ments with £. col i K-12 vectors if the major habitats of the given 
host-vector overlap those of E_. col i . If the host-vector has a major 
habitat that does not overlap those of E_. col i (e.g., root nodules 
in plants), then the containment conditions for some eukaryotic 
recombinant DNAs should be increased (for instance, higher plants 
and their viruses in the preceding example), while others may be 
reduced . 
4. Experiments with eukaryotic host-vectors 
<a> Animal host-vector systems - Because host cell lines generally 
have little if any capacity for propagation outside the laboratory, the 
primary focus for containment is the vector, although cells should also be 
derived from cultures expected to be of minimal hazard. Given good micro- 
biological practices, the most likely mode of escape of recombinant DNAs 
from a physically contained laboratory is carriage by humans; thus vectors 
[ 105 ] 
