Host mutants resistant to phage lambda killing

Host mutants have been isolated which are resistant to killing by the kil protein of an induced λ prophage. In general, such host mutants are defective in adsorption and production of lambdoid phages, and show altered sensitivities to deoxycholate, colicins, and antibiotics. Most of the mutants are cold sensitive and form filaments at the restrictive temperature. These properties seem to implicate the cell envelope in the kil phenomenon. The cold-sensitive host mutants cannot be cured of their prophage; furthermore, growth of the mutants at different temperatures shows a marked negative correlation with the degree of repressor activity of the temperature-sensitive cI857 repressor. These observations suggest that some phage product, perhaps kil protein, is required for cell survival in these mutants.