The effect of amino acids on host-controlled restriction of lambda phage

Abstract

Phage lambda grown in Escherichia coli C (λ·C) plates with an efficiency of ∼4 × 10 −4 on log phase E. coli K12 grown in broth. These few successful infections occur in “special cells” in the K12 population which have lost their ability to restrict λ·C. E. coli K12 grown in minimal medium has 30–50 times as many special cells. Supplementation of minimal medium with an amino acid mixture reduced the frequency of special cells to that observed in broth cultures. When amino acids were tested individually, the addition of either alanine or leucine alone to minimal medium reduced the special cell population. This reduction in the frequency of special cells was reversed by the further addition of several other amino acids to the growth medium. Medium shift experiments with alanine and leucine suggest that these amino acids do not act at the time of infection; instead they determine the presence of a metabolic system involved in the expression of host-controlled restriction. Removal of methionine from K12 cultures containing an otherwise complete amino acid mixture caused an increase in the number of special cells. Unlike the alanine and leucine effects, this increase was rapid and occurred in the presence of chloramphenicol. Prolonged growth in methionine was required to restore the reduced special cell frequency. It appears that the removal of methionine can convert a restricting cell into a special cell which is then incapable of undergoing cell division. The various amino acid effects are specific to the K12-restriction system and do not influence the B- or P1-restriction systems of E. coli.