SUMMARY: In contrast to the failure of several previous workers to transduce streptomycin resistance, it was found that streptomycin indifference (one-step complete resistance) could quite reproducibly be transduced. For the expression of indifference after transduction, the infected bacteria must be allowed to divide at least once. This finding is assumed to reflect a segregation delay because of the recessive nature of the indifference locus. But from the fact that transduced indifference is phenotypically expressed from partial to complete resistance, the participation of a phenomic lag is also assumed.

In addition to the delay of phenotypic expression, several other aspects of transduction of indifference were studied and a close similarity of the behaviour of indifference to other chromosomal markers was found.

The transduction of one-step intermediate resistance into sensitive and into other one-step intermediate resistant recipients, however, was found to be difficult to demonstrate if it occurs at all. The difficulty of detecting resistant transductants is apparently not due to the killing of resistant bacteria in the presence of sensitive cells.

The difficulty of transducing intermediate resistance is assumed to be due to a selective disadvantage of the resistant, slow-growing transductants. The failure to find transductions even with slow-growing sensitive recipients may have been due to the fact that successful transductions yielded even slower growing resistant clones.

On the other hand, the transduction of second-step resistance into one-step resistant mutants was found to take place and the transduction of indifference into one-step resistant bacteria yielded slow-growing indifferent transductants.


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