Colicin Biology

Abstract

SUMMARY Colicins are proteins produced by and toxic for some strains of Escherichia coli. They are produced by strains of E. coli carrying a colicinogenic plasmid that bears the genetic determinants for colicin synthesis, immunity, and release. Insights gained into each fundamental aspect of their biology are presented: their synthesis, which is under SOS regulation; their release into the extracellular medium, which involves the colicin lysis protein; and their uptake mechanisms and modes of action. Colicins are organized into three domains, each one involved in a different step of the process of killing sensitive bacteria. The structures of some colicins are known at the atomic level and are discussed. Colicins exert their lethal action by first binding to specific receptors, which are outer membrane proteins used for the entry of specific nutrients. They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system. The components of each system are known, and their implication in the functioning of the system is described. Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA. The mechanisms of inhibition by specific and cognate immunity proteins are presented. Finally, the use of colicins as laboratory or biotechnological tools and their mode of evolution are discussed.

What traits are carried on mobile genetic elements, and why?

“…In contrast, if plasmids are too rare, then there would be insufficient toxin and subsequent killing to compensate for the fixed costs of toxin production (Chao and Levin, 1981). The targets of bacteriocins are not always the same bacterial strain (Cascales et al, 2007). This presents an additional function for bacteriocin-carrying plasmids; if they are less efficient at infecting other strains, any plasmids that produce toxins to kill those strains will have an advantage from reducing competition with the strain it can more efficiently infect.…”

ef1097 and ypkK encode enterococcin V583 and corynicin JK, members of a new family of antimicrobial proteins (bacteriocins) with modular structure from Gram-positive bacteria

“…Thus, it would seem that the hitherto unrecognized ability of Gram-positive bacteria to produce large proteinaceous antibiotics (bacteriocins) is relatively widely distributed. Indeed, it is tempting to speculate that this family of protein antibiotics may represent the Grampositive equivalent of the colicin family in Gram-negative bacteria (Cascales et al, 2007).…”

“…Although from a biochemical perspective they exhibit an extraordinary diversity of structure, the bacteriocins can be loosely grouped into four categories, based on their molecular mass and whether the producing organism is Gram-positive or Gramnegative. For example, a number of species of the Enterobacteriaceae produce large, modular, antimicrobial proteins (M r .10 000) known as colicins (Cascales et al, 2007), whilst others produce relatively lower molecular mass antimicrobial peptides (M r ,10 000) termed microcins (Heng & Jack, 2006). Similarly, a veritable plethora of modified and unmodified peptide bacteriocins (M r ,10 000) from Gram-positive bacteria have also been described, particularly those elaborated by the lactic acid bacteria (Bonelli et al, 2006;Nes et al, 2006;Heng et al, 2007).…”

Pore-forming pyocin S5 utilizes the FptA ferripyochelin receptor to kill Pseudomonas aeruginosa

“…The Gram-negative bacterium Escherichia coli is one of the best documented organisms with regard to microbial allelopathy. The bacteriocins it produces, termed colicins, were first discovered and identified by the Belgian researcher André Gratia in 1925 (reviewed by Cascales et al, 2007). The bacteriocins produced by Pseudomonas species are called pyocins, and, in contrast to colicins whose genes are plasmid-borne, the pyocin genes are found in the chromosome (Sano & Kageyama, 1984;Shinomiya et al, 1983).…”