Irreversible binding of bacteriophage T5 to its FhuA receptor protein is associated with covalent cross-linking of 3 copies of tail protein pb4

Dual Predation by Bacteriophage and Bdellovibrio bacteriovorus Can Eradicate Escherichia coli Prey in Situations where Single Predation Cannot

Bacteria are preyed upon by diverse microbial predators, including bacteriophage and predatory bacteria, such as Bdellovibrio bacteriovorus While bacteriophage are used as antimicrobial therapies in Eastern Europe and are being applied for compassionate use in the United States, predatory bacteria are only just beginning to reveal their potential therapeutic uses. However, predation by either predator type can falter due to different adaptations arising in the prey bacteria. When testing poultry farm wastewater for novel Bdellovibrio isolates on Escherichia coli prey lawns, individual composite plaques were isolated containing both an RTP (rosette-tailed-phage)-like-phage and a B. bacteriovorus strain and showing central prey lysis and halos of extra lysis. Combining the purified phage with a lab strain of B. bacteriovorus HD100 recapitulated haloed plaques and increased killing of the E. coli prey in liquid culture, showing an effective side-by-side action of these predators compared to their actions alone. Using approximate Bayesian computation to select the best fitting from a variety of different mathematical models demonstrated that the experimental data could be explained only by assuming the existence of three prey phenotypes: (i) sensitive to both predators, (ii) genetically resistant to phage only, and (iii) plastic resistant to B. bacteriovorus only. Although each predator reduces prey availability for the other, high phage numbers did not abolish B. bacteriovorus predation, so both predators are competent to coexist and are causing different selective pressures on the bacterial surface while, in tandem, controlling prey bacterial numbers efficiently. This suggests that combinatorial predator therapy could overcome problems of phage resistance.IMPORTANCE With increasing levels of antibiotic resistance, the development of alternative antibacterial therapies is urgently needed. Two potential alternatives are bacteriophage and predatory bacteria. Bacteriophage therapy has been used, but prey/host specificity and the rapid acquisition of bacterial resistance to bacteriophage are practical considerations. Predatory bacteria are of interest due to their broad Gram-negative bacterial prey range and the lack of simple resistance mechanisms. Here, a bacteriophage and a strain of Bdellovibrio bacteriovorus, preyed side by side on a population of E. coli, causing a significantly greater decrease in prey numbers than either alone. Such combinatorial predator therapy may have greater potential than individual predators since prey surface changes selected for by each predator do not protect prey against the other predator.

Quantitative time-resolved measurement of membrane protein-ligand interactions using microcantilever array sensors

Membrane proteins are central to many biological processes, and the interactions between transmembrane protein receptors and their ligands are of fundamental importance in medical research. However, measuring and characterizing these interactions is challenging. Here we report that sensors based on arrays of resonating microcantilevers can measure such interactions under physiological conditions. A protein receptor--the FhuA receptor of Escherichia coli--is crystallized in liposomes, and the proteoliposomes then immobilized on the chemically activated gold-coated surface of the sensor by ink-jet spotting in a humid environment, thus keeping the receptors functional. Quantitative mass-binding measurements of the bacterial virus T5 at subpicomolar concentrations are performed. These experiments demonstrate the potential of resonating microcantilevers for the specific, label-free and time-resolved detection of membrane protein-ligand interactions in a micro-array format.

Complete genome sequence of bacteriophage T5

The 121,752-bp genome sequence of bacteriophage T5 was determined; the linear, double-stranded DNA is nicked in one of the strands and has large direct terminal repeats of 10,139 bp (8.3%) at both ends. The genome structure is consistently arranged according to its lytic life cycle. Of the 168 potential open reading frames (ORFs), 61 were annotated; these annotated ORFs are mainly enzymes involved in phage DNA replication, repair, and nucleotide metabolism. At least five endonucleases that believed to help inducing nicks in T5 genomic DNA, and a DNA ligase gene was found to be split into two separate ORFs. Analysis of T5 early promoters suggests a probable motif AAA{3, 4 T}nTTGCTT{17, 18 n}TATAATA{12, 13 W}{10 R} for strong promoters that may strengthen the step modification of host RNA polymerase, and thus control transcription of phage DNA. The distinct protein domain profile and a mosaic genome structure suggest an origin from the common genetic pool.

Overproduced and purified receptor binding protein pb5 of bacteriophage T5 binds to the T5 receptor protein FhuA

A promotor-less oad gene of bacteriophage T5, encoding the receptor binding protein pb5, was cloned into pT7-3 under the control of phage T7 promoter phi 10. Induction with IPTG resulted in enhanced production of pb5. Upon fractionation of the producing cells, most of the overproduced pb5 was found in the membrane fraction, which was most likely due to aggregation of the protein. The minor, soluble fraction of pb5 specifically inhibited adsorption of T5 to its FhuA receptor protein. Inhibition was also seen with trace amounts of pb5, and binding of pb5 to FhuA appeared to be almost irreversible. Purification of pb5 from the cytosolic fraction was performed by FPLC using a MonoQ column. pb5, which did not bind to the matrix of the column, was obtained in almost pure form. The purified protein also inhibited T5 adsorption.

Cloning, sequencing, and recombinational analysis with bacteriophage BF23 of the bacteriophage T5 oad gene encoding the receptor-binding protein

Binding of bacteriophage T5 to its receptor, the Escherichia coli FhuA protein, is mediated by tail protein pb5. In this article we confirm that pb5 is encoded by the T5 oad gene and describe the isolation, expression, and sequencing of this gene. In order to locate oad precisely, we analyzed recombinants between BF23, a T5-related phage with a different host range, and plasmid clones containing segments of the T5 chromosome. This analysis also showed that oad has little or no homology with hrs, the analogous BF23 gene. We were able to overproduce a protein that comigrates with pb5 after fusing a 2-kb segment containing oad to a phage T7 promoter. This segment contains an open reading frame that can encode a protein of the appropriate size. Its deduced amino acid sequence does not closely resemble that of any other protein in the database. The sequence upstream of the open reading frame shows typical characteristics of a promoter region with two overlapping, divergently orientated promoters.