SUMMARY: E colicins are those inactive on mutants, which lack the outer membrane protein that adsorbs vitamin B12, E colicins and phage BF23; types E1, E2, E3 and E7 have been defined by the specific immunity of E-colicinogenic strains to the type of E colicin they produce. Further immunity types - E4, E5 and E6 - are now described. of colicin type 9 makes colicin E4, and of types 9A, 12 and 14 make colicin E6 (not colicin E3, as previously supposed). Many local isolates make E colicin of a new type - E5. The action of colicins E1 to E7 was (incompletely) blocked by vitamin B12, which also reduced the effect of A colicins (which are weakly active on K12 indicators). K12 given plasmid ColA-23 by transformation was immune to A colicins but sensitive to colicins E1 to E7. A purported ‘colicin E4’ was shown to be of class colicin A. K12(CloDF13) transformants were immune to colicin E6. A ‘cap’ of colicin-sensitive indicator bacteria developed over, but not around, killed colonies of E-colicinogenic strains, because of adsorption of colicin by non-induced bacteria of the colony. Killed colonies of E-colicinogenic strains gave partly discrete lobes of colicin action on indicator lawns, instead of circular zones, apparently as a result of unstable variation in colicin production. The presence of a colicin E4, E5 or E6 plasmid in K12 strains made them more sensitive to colicins E2 and E7, as shown by zones of partial translucency surrounding the ordinary colicin zones and by increased titre of colicin E2 and E7 preparations on such indicators.


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