The Rex system of bacteriophage lambda: tolerance and altruistic cell death.

Abstract

The rexA and rexB genes of bacteriophage A. encode a two-component system that aborts lytic growth of bacterial viruses. Rex exclusion is characterized by termination of macromolecular synthesis, loss of active transport, the hydrolysis of ATP, and cell death. By analogy to colicins El and K, these results can be explained by depolarization of the cytoplasmic membrane. We have fractionated cells to determine the intracellular location of the RexB protein and made RexB-alkaline phosphatase fusions to analyze its membrane topology. The RexB protein appears to be a polytopic transmembrane protein. We suggest that RexB proteins form ion channels that, in response to lytic growth of bacteriophages, depolarize the cytoplasmic membrane. The Rex system requires a mechanism to prevent X itself from being excluded during lytic growth. We have determined that overexpression of RexB in A. lysogens prevents the exclusion of both T4 rll mutants and X ren mutants. We suspect that overexpression of RexB is the basis for preventing self-exclusion following the induction of a \ lysogen and that RexB overexpression is accomplished through transcriptional regulation.

Altruism can evolve when relatedness is low: evidence from bacteria committing suicide upon phage infection

“…Our findings are in close agreement with the work of Fukuyo et al [33], who used an engineered E. coli-phage system to demonstrate for the first time that host suicide is adaptive in structured habitats. Our study and the work of Fukuyo et al [33] contrast with previous studies, where evolutionary conclusions were mainly based on proximate (mechanistic) aspects of cell death [8,10,11]. This is problematic because mechanistic approaches elucidating how things work can provide only limited answers on why a given behaviour has evolved [31].…”

“…Furthermore, it is also unclear whether this form of dormancy is adaptive, providing direct fitness benefits, or whether it represents a by-product of the Rex system, which has primarily evolved to induce suicide. The latter explanation seems more probable, because the mechanism of cell death is clearly established [8,13] and is triggered across most conditions examined here.…”

“…From an evolutionary perspective, the expression of an Abi system could reflect an altruistic act that allows infected bacteria to commit suicide in order to prevent parasite transmission to nearby relatives. Bacteria possess a number of Abi mechanisms, which usually involve joint actions by a prophage (a phage integrated into the bacterial genome) or a plasmid that encodes the genes for the abortive infection, and the bacterium, which transcribes and synthesizes the abortive machinery [7][8][9][10][11]. Important to note is that in many cases the interests of the bacterium and an already resident prophage become completely aligned upon obligately lytic phage infection (i.e.…”

“…Although Abi systems have long been considered by some to reflect altruistic acts [8], a rigorous test involving the measurement of parameters of Hamilton's rule is lacking. We accomplished this by measuring the benefit and cost of suicide, as well as the effect of relatedness on suicide in E. coli carrying the prophage l (henceforth E. coli l), which encodes the Rex abortive infection system [13].…”

Diverse Functions of Restriction-Modification Systems in Addition to Cellular Defense

“…The Rex system of E. coli, which contains two components, viz., RexA and RexB, is one of the most well-studied abortive infection systems to date (43,44). Upon phage infection, a replication complex intermediate activates RexA.…”