b). Transduction of streptomycin sensitivity into resistant mutants oE Salmonella typhimurium

SUMMARY: The infection of slow-growing one-step intermediate streptomycin-resistant mutants with phage from wild-type bacteria, indifferent (one-step com-pletely resistant) or other one-step intermediate resistant mutants gives rise to fast-growing streptomycin-sensitive transductants. From this fact it is clear that both slow growth and streptomycin resistance are controlled by a single locus. The transductants are very easily detected on the poor background growth of the inter-mediate resistant recipient. With this technique it has become possible to cross one-step resistance with resistance, indifference and sensitivity. The results so far obtained indicate that one-step intermediate resistance is controlled by multiple loci. None of these loci is linked to the indifference locus. The fast-growing mutants which develop from the two-step resistant mutants are assumed from the trans-duction analysis to be due to reverse mutations at the first step loci. In a preceding paper Watanabe & Watanabe (1959) reported that streptomycin indifference (one-step complete resistance) is easily transduced into sensitive or intermediate resistant bacteria. On the other hand, the transduction int