Abstract
By using the method of sib selection followed by the replica-plating, a cadmium resistant clone (r1) was isolated from a sensitive strain (Par), and a clone of a higher resistance level (r2) from r1. Thus, r1 and r2 were shown to be of pre-adaptive nature. However, the strain of still higher resistance, obtainable by culturing in the presence of cadmium, has not been isolated by the indirect selection.
The mutation rate from Par to r1 and that from r1 to r2 were 6.3×10-9 and 4.0× 10-8 per cell per budding cycle, respectively. Growth of r1 was slower than Par, and r2 than r1, in their mixed cultures.
r1 was more resistant to copper, cobalt and nickel than Par, but r2 was less so than r1 except for nickel.
