Phage T1-mediated transduction of a plasmid containing the T1 pac site

Phages for treatment of Escherichia coli infections

Diseases due to infections by pathogenic Escherichia coli strains are on the rise and with the growing antimicrobial resistance among bacterial pathogens, including this group. Thus, alternative therapeutic options are actively investigated. Among these alternatives is phage therapy. In the case of E. coli, the combination of the well understood biology of this species and its bacteriophages represents a good guiding example for the establishment of phage therapy principles against this and other pathogenic bacteria. In this chapter, the procedures toward the development of phage therapy against pathogenic E. coli with the use of T-even group of phages are discussed. These steps involve the isolation, purification, characterisation and large-scale production of these phages, with formulation of phage cocktails for in vitro and in vivo studies. The main emphasis is made on phage therapy of enteropathogenic E. coli O157:H, which is one of the prominent human pathogens but persists as a commensal bacterium in many food animals. The implementation of phage therapy against E. coli O157:H within the One Health framework in carrier animals and for treatment of meat, vegetables, fruits and other agricultural produce thus would allow controlling and interrupting the transmission routes of this pathogen to the human food chain and preventing human disease. Examples of successful control and elimination of E. coli O157:H are given, while the problems encountered in phage treatment of this pathogen are also discussed.

Function and horizontal transfer of the small terminase subunit of the tailed bacteriophage Sf6 DNA packaging nanomotor

Bacteriophage Sf6 DNA packaging series initiate at many locations across a 2kbp region. Our in vivo studies show that Sf6 small terminase subunit (TerS) protein recognizes a specific packaging (pac) site near the center of this region, that this site lies within the portion of the Sf6 gene that encodes the DNA-binding domain of TerS protein, that this domain of the TerS protein is responsible for the imprecision in Sf6 packaging initiation, and that the DNA-binding domain of TerS must be covalently attached to the domain that interacts with the rest of the packaging motor. The TerS DNA-binding domain is self-contained in that it apparently does not interact closely with the rest of the motor and it binds to a recognition site that lies within the DNA that encodes the domain. This arrangement has allowed the horizontal exchange of terS genes among phages to be very successful.

Transduction of a Plasmid Carrying the Cohesive End Region from Lactococcus lactis Bacteriophage PhiLC3

Plasmids carrying the cohesive end region from temperate lactococcal bacteriophage PhiLC3 could be packaged in vivo by PhiLC3 and transduced into its host strain, Lactococcus lactis subsp. cremoris NCDO 1201. The transduction frequencies were between 10 and 10 transducing particles per PFU, depending on the size of the phage DNA insert. This transduction system is limited to only certain lactococcal strains. The PhiLC3 cohesive site region (cos) appears to play an important role in plasmid transduction.

High-Frequency Plasmid Transduction by Lactobacillus gasseri Bacteriophage phiadh

The temperate bacteriophage phiadh mediates plasmid DNA transduction in Lactobacillus gasseri ADH at frequencies in the range of 10 to 10 transductants per PFU. BglII-generated DNA fragments from phage phiadh were cloned into the BclI site of the transducible plasmid vector pGK12 (4.4 kb). Phage phiadh lysates induced from Lactobacillus lysogens harboring pGK12 or the recombinant plasmids were used to transduce strain ADH to chloramphenicol resistance. The transduction frequencies of recombinant plasmids were 10- to 10-fold higher than that of native pGK12. The increase in frequency generally correlated with the extent of DNA-DNA homology between plasmid and phage DNAs. The highest transduction frequency was obtained with plasmid pTRK170 (6.6 kb), a pGK12 derivative containing the 1.4- and 0.8-kb BglII DNA fragments of phiadh. DNA hybridization analysis of pTRK170-transducing phage particles revealed that pTRK170 had integrated into the phiadh genome, suggesting that recombination between homologous sequences present in phage and plasmid DNAs was responsible for the formation of high-frequency transducing phage particles. Plasmid DNA analysis of 13 transductants containing pTRK170 showed that each had acquired intact plasmids, indicating that in the process of transduction a further recombination step was involved in the resolution of plasmid DNA monomers from the recombinant pTRK170::phiadh molecule. In addition to strain ADH, pTRK170 could be transduced via phiadh to eight different L. gasseri strains, including the neotype strain, F. Gasser 63 AM (ATCC 33323).

Effective plasmid pX3 transduction in Lactobacillus delbrueckii by bacteriophage LL-H

High-frequency plasmid transductions in Lactobacillus delbrueckii subsp. lactis and subsp. bulgaricus strains mediated by pac-type bacteriophages were observed and further investigated. The frequency of plasmid transduction by phages LL-H and LL-S attained levels of from 0.10 to about 1 with plasmid p X 3, but only about 2 x 10(-2) with plasmid pJK650. Infection of L. delbrueckii subsp. lactis strain LKT(pX3) or ATCC 15808(pX3) with phage LL-H resulted in intensive concatemerization of plasmid pX3, and most progeny phage particles contained concatemers of plasmid DNA instead of phage LL-H DNA. The synthesis of phage LL-H DNA was depressed. No evident homology or recombination was observed between phage LL-H DNA and plasmid pX3. The unusually high frequency of plasmid pX3 transduction by phage LL-H could be considered to result from specific interaction(s) between a particular phage and plasmid. These interactions may include pX3-mediated blockage of phage LL-H DNA replication and effective use of a particular pac-like site located about 1 kb from BglII in the smaller NdeI-BglII fragment of plasmid pX3. Phage LL-H together with plasmid vector pX3 could be used as effective plasmid transduction tools for genetic engineering of L. delbrueckii subsp. lactis and subsp. bulgaricus strains.

Recombination-dependent concatemeric plasmid replication

The replication of covalently closed circular supercoiled (form I) DNA in prokaryotes is generally controlled at the initiation level by a rate-limiting effector. Once initiated, replication proceeds via one of two possible modes (theta or sigma replication) which do not rely on functions involved in DNA repair and general recombination. Recently, a novel plasmid replication mode, leading to the accumulation of linear multigenome-length plasmid concatemers in both gram-positive and gram-negative bacteria, has been described. Unlike form I DNA replication, an intermediate recombination step is most probably involved in the initiation of concatemeric plasmid DNA replication. On the basis of structural and functional studies, we infer that recombination-dependent plasmid replication shares important features with phage late replication modes and, in several aspects, parallels the synthesis of plasmid concatemers in phage-infected cells. The characterization of the concatemeric plasmid replication mode has allowed new insights into the mechanisms of DNA replication and recombination in prokaryotes.

The generation of concatemeric plasmid DNA in Bacillus subtilis as a consequence of bacteriophage SPP1 infection

Bacteriophage SPP1 infection of Bacillus subtilis cells bearing plasmids induces the synthesis of multigenome-length plasmid molecules. Two independent pathways can account for this synthesis. In one of those, homology to the phage genome is required, whereas in the other such homology is not a prerequisite. In wild type cells both modes overlap. In dnaB(Ts), at non permissive temperature, or in recE polA strains the main concatemeric plasmid replication mode is the homology-dependent plasmid (hdp) mode. The rate of recombination-dependent concatemeric plasmid DNA synthesis is a consequence of a phage-plasmid interaction which leads to chimeric phage::plasmid DNA. The second mode, which is an homology-independent plasmid (hip) mode seems to be triggered upon the synthesis of a phage encoded product(s) (e.g. inactivation of the exonuclease V enzyme).