CHARACTERIZATION OF CONJUGATION FACTORS IN ESCHERICHIA COLI CELL WALLS. I. INHIBITION OF RECOMBINATION BY CELL WALLS AND CELL EXTRACTS

Natural and Artificial Strategies To Control the Conjugative Transmission of Plasmids

Conjugative plasmids are the main carriers of transmissible antibiotic resistance (AbR) genes. For that reason, strategies to control plasmid transmission have been proposed as potential solutions to prevent AbR dissemination. Natural mechanisms that bacteria employ as defense barriers against invading genomes, such as restriction-modification or CRISPR-Cas systems, could be exploited to control conjugation. Besides, conjugative plasmids themselves display mechanisms to minimize their associated burden or to compete with related or unrelated plasmids. Thus, FinOP systems, composed of FinO repressor protein and FinP antisense RNA, aid plasmids to regulate their own transfer; exclusion systems avoid conjugative transfer of related plasmids to the same recipient bacteria; and fertility inhibition systems block transmission of unrelated plasmids from the same donor cell. Artificial strategies have also been designed to control bacterial conjugation. For instance, intrabodies against R388 relaxase expressed in recipient cells inhibit plasmid R388 conjugative transfer; pIII protein of bacteriophage M13 inhibits plasmid F transmission by obstructing conjugative pili; and unsaturated fatty acids prevent transfer of clinically relevant plasmids in different hosts, promoting plasmid extinction in bacterial populations. Overall, a number of exogenous and endogenous factors have an effect on the sophisticated process of bacterial conjugation. This review puts them together in an effort to offer a wide picture and inform research to control plasmid transmission, focusing on Gram-negative bacteria.

Isolation and characterization of Escherichia coli K-12 F- mutants defective in conjugation with an I-type donor

Escherichia coli K-12 F- mutants defective in conjugation with an I-type donor (ConI-) were isolated and characterized. These mutants are specific in that they are conjugation proficient with other types of donor strains. They have an altered susceptibility to phages and detergents. Chemical analysis of the cell envelopes of mutant strains has shown that the lipopolysaccharide (LPS) is altered and that one major outer-membrane protein is absent. Conjugation experiments in which LPS from wild-type cells was added to a mating mixture, made up with wild-type donor and recipient cells, showed inhibition in transconjugant formation when an I-type donor, but not an F-type donor, was used. This strongly suggests that LPS of the recipient cell is directly involved in the ability to mate with an I-type donor but not with an F-type donor. The mutations are located in the 78- to 82-min region of the E. coli map, with one exception where the mutation maps near or in the galactose operon.

Effect of Zn2+ on bacterial conjugation: increase in ability of F- cells to form mating pairs

Incubation of F(-) cells at 37 C with 10(-3) M Zn(2+) before mating was found to increase the ability of F(-) cells to form mating pairs when mated. This increased pair-forming ability is persistent, at least for the duration of mating. The F(-) cells with increased pair-forming ability obtained by the 10(-3) M Zn(2+) treatment can form mating pairs efficiently with males from which F pili were removed or inactivated with 10(-3) M Zn(2+).