20 
c) In addition , " The feeding of tetracycline to rats for one 
day prior to and during feeding of X*876 results in survival of some X1876 
cells." (Curtiss e^ ,al. , p.21) This is astonishing, for it seems that the 
presence of the pSClOl plasmid, by virtue of its tetracycline-resistance 
marker, enables X1776 (xl876) to survive passage through the rat gut in the 
presence of tetracycline. Furthermore, this phenotype overrides all of 
the mutational barriers ( dapD 8, thyA 57, A40, rfb-2) intentionally 
established to prevent survival. These data. are even more surprising 
in that they do not consider the inactivation of tetracycline iji^ vivo 
by the milk in which the strains were administered. In addition, a bile 
salts resistant derivative of xl^76 (which occurred upon spontaneous 
reversion of xl^76, see this paper, §7) gives higher survival titers 
under the same conditions. 
Potential for Transmissability of Genetic Information by Stra ins : 
§15. Conjugational recipient ability under permissive conditions: 
Of the 14 plasmid” incompatability groups examined, 9 are 
reduced less than ICO fold and 6 are reduced less than 20 fold in their 
proficiency to serve as donors to X^776 at at least one of the two 
temperatures, 32°C and 37°C (Curtiss £j: al^. , Table 18, Appendix A). 
§16. Mobilization of pSClOl by conjugative plasmids under permissive 
conditions : 
X1876 exhibits the same donor ability as the parent y!753 
under permissive conditions for 5 out of the 7 plasmids tested 
(Curtiss et al., p.24, Appendix A). Moreover, since phenotypic expression 
of the tetracycline marker on the pSClOl plasmid was not allowed for in the 
[Appendix C — 208] 
