A genetic study of tolerance and resistance to colicin A in Citrobacter freundii

Colicin A-insensitive mutants of Citrobacter freundii were isolated and grouped into six phenotypic classes characterized by sensitivity, insensitivity or partial insensitivity to the bacteriocins S6, DF 13 and colicin A, and sensitivity or insensitivity to deoxycholate (DOC) and ampicillin. Mapping by the gradient-of-transmission method revealed the chromosomal regions in which the responsible genes are situated. Res-3 mapped near pur between pur and thr; Tol-5 mapped between aro and ilv and Tol-4 between gal and pur; Tol-1, Tol-2 and Tol-3 are situated close to gal. All the mutations that mapped near gal rendered the bacteria more sensitive to DOC and ampicillin. Complementation analysis with E. coli plasmids showed that the three phenotypic groups that map near gal were complemented by E. coli plasmids and fall into three complementation groups. Two of these are quivalent with the tol A and tol B genes in E. coli.