Studies on polylysogens containing λN−cI− prophages II. Role of high multiplicities in lysogen formation by λN−cI− phage

Abstract

Results of the experiments presented in this paper show that λN−cI− phage can lysogenize a nonpermissive host Escherichia coli when it infects at very high multiplicities (around 100), and λN−cI−cII− and λcIII−N−cI− lysogenize poorly at similar high multiplicities. The latter two phages lysogenize with appreciable frequency when either λN−cI− or λint-cN−cI−cII− is used as helper. The phages, λN−cI−, λN−cI−cII−, and λcIII−N−cI− can lysogenize also at relatively low m.o.i. of 20 in presence of the above λint-c helper, and the λint-cN−cI−cII− phage alone forms converted lysogens at an m.o.i. as low as 12. All these results suggest that the establishment of prophage integration by λN−cI− is positively regulated, like λN+cI+ phage, by the cII/cIII-promoted expression of the int gene of λ, and under the N− condition, high multiplicities are needed to provide optimum levels of cII and cIII products, especially the latter.