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A new colicin, as defined by cross-immunity tests against the colicin reference set, has been identified from a uropathogenic Escherichia coli isolate (strain 2424), collected from a pyelonephritis patient at Christchurch Hospital. This toxin, colicin 24, is active against E. coli and Salmonella typhimurium, and the genes involved in colicin 24 production, transport, and immunity were found to reside on a 43.54-kb conjugative plasmid, p24-2. Mutagenesis using mini-Tn10 has identified two consecutive EcoR1 fragments on p24-2 that contain all the colicin 24 determinants. A 25.14-kb BamHl-HindIII fragment containing this region was cloned from a mutant with a normal colicin phenotype into pBR322 to form the recombinant plasmid pGOB34. Subcloning of pGOB34 has resulted in an 8.7-kb fragment containing all the colicin 24 determinants being cloned into pUC18 to form pGOB342. Copyright 1994, 1999 Academic Press

The colicin V production and immunity genes were isolated from plasmid pColV-K30. A HindIII-to-SalI fragment of 9.4 kilobases was cloned into the compatible vectors pBR322 and pACYC184. Mutants defective in colicin production were generated by Tn5 insertions and by constructing deletions in vitro. Physical analysis of these mutations identified a 4.4-kilobase region of this DNA which contains all the plasmid genes (cva) needed for the production of colicin V. The colicin V immunity determinant (cvi) is in a 700-base-pair fragment located within one end of this region. Complementation tests identified three genes, called cvaA, cvaB, and cvaC, required for colicin production. Analysis of the proteins labeled in minicells harboring various Tn5 insertions allowed us to identify protein products for the cvaA and cvaC genes. Mutations in cvaA and cvaB eliminated colicin activity in culture supernatants, but not within the cells. Mutations in cvaC, however, eliminated all detectable activity. From these results we conclude that the cvaC gene codes for the structural gene for colicin V, while cvaA and cvaB are apparently needed for the normal export of the colicin.

A mini-Tn10-kan insertion mutation identified a gene in the chromosome of Escherichia coli required for colicin V production from plasmid pColV-K30. With the complete restriction map of E. coli, the mutation was rapidly mapped to 50.0 min, within the purF operon. Sequence analysis showed that the insertion occurred in a gene with no previously known function which is located directly upstream of purF. We designated this gene cvpA for colicin V production. The mutant requires adenine for growth, probably because of a polar effect on purF expression. However, an adenine auxotroph showed no defect in colicin V production, suggesting that the cvpA mutation is responsible for the effect on colicin V production. Two possible models of cvpA1 allele function are discussed.

WE have been studying the effects of polychlorinated biphenyls (PCBs) and DDT on several planktonic algae, and report here that we have isolated a kanamycin-resistant strain of Scenedesmus obliquuswhich shows simultaneous resistance to other antibiotics, PCBs and Cetavlon (ICI), a quaternary ammonium compound with algicidal properties2. This novel observation suggests a possible genetic control of sensitivity to PCBs in Scenedesmus.