THE ROLE OF HOST‐CELL REPAIR IN LIQUID‐HOLDING RECOVERY OF U.V.‐IRRADIATED ESCHERICHIA COLI

Abstract

Abstract— The experiments reported give evidence that liquid‐holding recovery (LHR) of u.v. irradiated E. coli cells involves basically the same type of dark repair which causes reactivation of phage and which results in much increased survival of the cells themselves [host‐cell reactivation (HCR)]. LHR is very small in the two HCR(‐) strains B syn‐ and Bs‐1, but occurs to larger but different extents in the three HCR(+) strains B, B/r, and B/r (Λ). LHR is inhibited if the liquid contains caffeine or acriflavine, both of which are known to inhibit HCR. The results indicate that most of the LHR effect, if not all, occurs during the liquid holding, rather than under growth conditions after liquid holding. It is assumed that the holding itself allows a prolonged time for, and therefore an enhancement of, HCR. It is thus implicit that LHR can be observed only where otherwise HCR of repairable u.v. damage would be incomplete, and that different extents of LHR, as observed in the three HCR(+) strains, reflect different extents of incompleteness of HCR. It is concluded that the repairable u.v. hits which are not fully repaired by HCR are predominantly those concerned with the extra u.v. sensitivity of the strains B and B/r (Λ), relative to B/r.