Mode of action of colicin S8.

The mode of action of colicin S8 has been studied and compared with that of other colicins. Two minutes after the addition of colicin S8 to bacteria a considerable proportion of the colicin is inaccessible to trypsin. Treatment of bacteria with colicin S8 renders them more sensitive to lysis by sodium dodecyl sulphate and also inhibits motility. Like colicins K and E1, colicin S8 provokes lysis of bacteria superinfected with bacteriophage T4. Colicin S8, unlike colicin E2, prevents replication of bacteriophage T4. The incorporation of isoleucine or uracil into bacteria is inhibited by colicin S8 but, unlike colicins K and E1, the effect is multiplicity-dependent. A rapid method of titration of colicin S8 is described. The results are discussed with emphasis on the possible rearrangements at the bacterial surface and the possibility that there is more than one type of specific receptor for colicin S8.