The outer membrane protein OmpA of Escherichia coli K-12 serves as a receptor for a number of T-even-like phages. We have isolated a series of ompA mutants which are resistant to such phages but which still produce the OmpA protein. None of the mutants was able to either irreversibly or reversibly bind the phage with which they had been selected. Also, the OmpA protein is required for the action of colicins K and L and for the stabilization of mating aggregates in conjugation. Conjugal proficiency was unaltered in all cases. Various degrees of colicin resistance was found; however, the resistance pattern did not correlate with the phage resistance pattern. DNA sequence analyses revealed that, in the mutants, the 325-residue OmpA protein had suffered the following alterations: Gly-65----Asp, Gly-65----Arg, Glu-68----Gly, Glu-68----Lys (two isolates), Gly-70----Asp (four isolates), Gly-70----Val, Ala-Asp-Thr-Lys-107----Ala-Lys (caused by a 6-base-pair deletion), Val-110----Asp, and Gly-154----Ser. These mutants exhibited a complex pattern of resistance-sensitivity to 14 different OmpA-specific phages, suggesting that they recognize different areas of the protein. In addition to the three clusters of mutational alterations around residues 68, 110, and 154, a site around residue 25 has been predicted to be involved in conjugation and in binding of a phage and a bacteriocin (R. Freudl, and S. T. Cole, Eur. J. Biochem, 134:497-502, 1983; G. Braun and S. T. Cole, Mol. Gen. Genet, in press). These four areas are regularly spaced, being about 40 residues apart from each other. A model is suggested in which the OmpA polypeptide repeatedly traverses the outer membrane in cross-beta structure, exposing the four areas to the outside.

Escherichia coli K-12 outer membrane protein (OmpA) as a bacteriophage receptor: analysis of mutant genes expressing altered proteins.

Facing frequent phage challenges, bacteria have evolved numerous mechanisms to resist phage infection A commonly used phage resistance strategy is abortive infection (Abi), in which the infected cell commits suicide before the phage can complete its replication cycle Abi prevents the phage epidemic from spreading to nearby cells, thus protecting the bacterial colony The Abi strategy is manifested by a plethora of mechanistically diverse defense systems that are abundant in bacterial genomes In turn, phages have developed equally diverse mechanisms to overcome bacterial Abi This review summarizes the current knowledge on bacterial defense via cell suicide It describes the principles of Abi, details how these principles are implemented in a variety of natural defense systems, and discusses phage counter-defense mechanisms

https://www.annualreviews.org/doi/pdf/10.1146/annurev-virology-011620-040628

Abortive Infection: Bacterial Suicide as an Antiviral Immune Strategy

We used a comparative genomics approach to identify genes that are under positive selection in six strains of Escherichia coli and Shigella flexneri, including five strains that are human pathogens. We find that positive selection targets a wide range of different functions in the E. coli genome, including cell surface proteins such as beta barrel porins, presumably because of the involvement of these genes in evolutionary arms races with other bacteria, phages, and/or the host immune system. Structural mapping of positively selected sites on trans-membrane beta barrel porins reveals that the residues under positive selection occur almost exclusively in the extracellular region of the proteins that are enriched with sites known to be targets of phages, colicins, or the host immune system. More surprisingly, we also find a number of other categories of genes that show very strong evidence for positive selection, such as the enigmatic rhs elements and transposases. Based on structural evidence, we hypothesize that the selection acting on transposases is related to the genomic conflict between transposable elements and the host genome.

/pdf/genes-under-positive-selection-in-escherichia-coli-1o8l39gcoe.pdf

Genes under positive selection in Escherichia coli

(Ph)ighting Phages: How Bacteria Resist Their Parasites

Theory predicts that selection for pathogen virulence and horizontal transmission is highest at the onset of an epidemic but decreases thereafter, as the epidemic depletes the pool of susceptible hosts. We tested this prediction by tracking the competition between the latent bacteriophage λ and its virulent mutant λcI857 throughout experimental epidemics taking place in continuous cultures of Escherichia coli. As expected, the virulent λcI857 is strongly favored in the early stage of the epidemic, but loses competition with the latent virus as prevalence increases. We show that the observed transient selection for virulence and horizontal transmission can be fully explained within the framework of evolutionary epidemiology theory. This experimental validation of our predictions is a key step towards a predictive theory for the evolution of virulence in emerging infectious diseases.

/pdf/evolution-of-virulence-in-emerging-epidemics-593wn6c11j.pdf

Evolution of virulence in emerging epidemics.

Gene lamB encodes the outer membrane receptor for phage lambda in Escherichia coli K12. We have determined the DNA sequence alterations of 17 lamB point mutations which result in resistance to phage lambda h+. The mutations correspond to four phenotypic classes according to the pattern of growth of three phages which use the lambda receptor: lambda h (a one-step host-range derivative of lambda h+), lambda hh* (a two-step host-range derivative of lambda h+) and K10 (another lambdoid phage). Fourteen mutations are of the missense type and correspond to Gly to Asp changes distributed as follows. One class I mutation is at position 382 of the mature lambda receptor. Seven class I* mutations, four of which at least are independent, are at position 401. Six independent class II mutations are at position 151. The three other (class III) mutations are of the nonsense type. They change codons TGG (Trp) into TAG (amber) at positions 120 (two mutations) and 351 (one mutation). Implications of these results for the topological organization of the lambda receptor as well as possible reasons for the limited number of altered sites detected are discussed.

https://www.embopress.org/doi/pdf/10.1002/j.1460-2075.1983.tb01384.x

Genetic study of a membrane protein: DNA sequence alterations due to 17 lamB point mutations affecting adsorption of phage lambda.

We describe a system for genetic analysis in gene lamb. It consists of a phage which allows mapping, complementation and sequencing studies of lamB mutations and of the sequence of gene lamB. We present results obtained with this system for a set of mutations conferring tight resistant to phage lambda. This leads to a first identification of three residues in the LamB protein which are important for adsorption of phage lambda h+. Residues 151 and 382 are important for reversible adsorption while residues 401 is important for irreversible adsorption. We briefly review other tight mutations affecting gene lamB and discuss some implications of the results on phage receptor interactions, LamB-protein structure and membrane insertion.

E. Lepouce

Papers

Genetic study of a membrane protein: DNA sequence alterations due to 17 lamB point mutations affecting adsorption of phage lambda.

A system for genetic analysis in gene lamB: first results with lambda-resistant tight mutants.