Lytic replication of coliphage lambda in Salmonella typhosa hybrids.

Hybrids between Escherichia coli K-12 and Salmonella typhosa which conserved a continuous K-12 chromosomal diploid segment extending from pro through ara to the strA locus were sensitive to plaque formation by wild-type lambda. These partially diploid S. typhosa hybrids could be lysogenized with lambda and subsequently induced to produce infectious phage particles. When the K-12 genes were segregated from a lysogenic S. typhosa hybrid, phage-productive ability was no longer detectable due to loss of a genetic region necessary for vegetative replication of lambda. However, lambda prophage was shown to persist in a quiescent state in the S. typhosa hybrid segregant with phage-productive ability being reactivated after replacement of the essential K-12 lambda replication region. Low-frequency transduction and high-frequency transduction lysates containing the gal(+) genes of S. typhosa were prepared by induction of lambda-lysogenic S. typhosa hybrids indicating that the attlambda site is chromosomally located in S. typhosa in close proximity to the gal locus as in E. coli K-12. After propagation in S. typhosa hybrids, lambda was subject to restriction by E. coli K-12 recipients, thus establishing that S. typhosa does not perform the K-12 modification of lambda deoxyribonucleic acid. Hybrids of S. typhosa, however, did not restrict lambda grown previously on E. coli K-12. The K-12 genetic region required for lambda phage production in S. typhosa was located within min 66 to min 72 on the genetic map of the E. coli chromosome. Transfer of an F-merogenote encompassing the 66 to 72 min E. coli chromosomal region to lambda-insensitive S. typhosa hybrids enabled them to replicate wild-type lambda. The lambda-insensitive S. typhosa hybrid, WR4255, which blocks lambda replication, can be mutagenized to yield mutant strains sensitive to lambdavir and lambdaimm434. These WR4255 mutants remained insensitive to plaque formation by wild-type lambda.

Behavior of coliphage lambda in hybrids between Escherichia coli and Salmonella.

Salmonella typhosa hybrids able to adsorb lambda were obtained by mating S. typhosa recipients with Escherichia coli K-12 donors. After adsorption of wild-type lambda to these S. typhosa hybrids, no plaques or infective centers could be detected. E. coli K-12 gal(+) genes carried by the defective phage lambdadg were transduced to S. typhosa hybrids with HFT lysates derived from E. coli heterogenotes. The lysogenic state which resulted in the S. typhosa hybrids after gal(+) transduction differed from that of E. coli. Ability to produce lambda, initially present, was permanently segregated by transductants of the S. typhosa hybrid. S. typhosa lysogens did not lyse upon treatment for phage induction with mitomycin C, ultraviolet light, or heat in the case of thermoinducible lambda. A further difference in the behavior of lambda in Salmonella hybrids was the absence of zygotic induction of the prophage when transferred from E. coli K-12 donors to S. typhosa. A new lambda mutant class, capable of forming plaques on S. typhosa hybrids refractory to wild-type lambda, was isolated at low frequency by plating lambda on S. typhosa hybrid WR4254. Such mutants have been designated as lambdasx, and a mutant allele of lambdasx was located between the P and Q genes of the lambda chromosome. Plaques were formed also on the S. typhosa hybrid host with a series of lambda(i21) hybrid phages which contain the N gene of phage 21. The significance of these results in terms of Salmonella species as hosts for lambda is discussed.