The use of phages as antibacterial agents is limited by their generally narrow host range. The aim of this study was to make a T4-like phage, WG01, obtain the host range of another T4-like phage, QL01, by replacing its host determinant gene region with that of QL01. This process triggered a direct expansion of the WG01 host range. The offspring of WG01 obtained the host ranges of both QL01 and WG01, as well as the ability to infect eight additional host bacteria in comparison to the wildtype strains. WQD had the widest host range; therefore, the corresponding QD fragments could be used for constructing a homologous sequence library. Moreover, after a sequencing analysis of gene37, we identified two different mechanisms responsible for the expanded host range: 1) the first generation of WG01 formed chimeras without mutations; and 2) the second generation of WG01 mutants formed from the chimeras. The expansion of the host range indicated that regions other than the C-terminal region may indirectly change the receptor specificity by altering the supportive capacity of the binding site. Additionally, we also found that the subsequent generations acquired a novel means of expanding the host range through acquiring a wider temperature range for lysis by exchanging gene37. The method developed in this work offers a quick way to change or expand the host range of a phage. Future clinical applications for screening phages against a given clinical isolate could be achieved after acquiring more suitable homologous sequences. T4-like phages have been established as safe in numerous phage therapy applications. The primary drawbacks to the use of phages as therapeutic agents include their highly specific host range. Thus, changing or expanding the host range of T4-like phages is beneficial for selecting phages for phage therapy. In this study, the host range of one T4-like phage WG01 was expanded using genetic manipulation. The WG01 derivatives acquired a novel means of expanding their host range through acquiring a wider temperature range for lysis. A region was located that had the potential to be used as a sequence region for homologous sequence recombination.

No abstract

The use of bacteriophages as therapeutic agents is hindered by their narrow and specific host range, and by a lack of the knowledge concerning the molecular mechanism of receptor recognition. Two P2-like coliphages, named P88 and pro147, were induced from Escherichia coli strains K88 and DE147, respectively. A comparison of the genomes of these two and other P2-like coliphages obtained from GenBank showed that the tail fiber protein genes, which are the key genes for receptor recognition in other myoviridae phages, showed more diversity than the conserved lysin, replicase, and terminase genes. Firstly, replacing hypervariable region 2 (HR2: amino acids 716–746) of the tail fiber protein of P88 with that of pro147 changed the host range of P88. Then, replacing six amino acids in HR2 with the corresponding residues from pro147 altered the host range only in these mutants with changes at position 730 (leucine) and 744 (glutamic acid). Thus, we predicted that these amino acids are vital to establish the host range of P88. This study provided a vector of lysogenic bacteria that could be used to change or expand the phage host range of P88. These results illustrated that, in P2-like phage P88, the tail fiber protein determined the receptor recognition. Amino acids 716–746 and the amino acids at positions 730 and 744 were important for receptor recognition.

No abstract