Scientists have for the first time manually synthesized bacteriophages with shortened genomes that lyse various strains of Pseudomonas aeruginosa . This experiment could be the first step toward creating new antibacterial agents.

Bacteriophages are currently considered promising antimicrobial agents, particularly relevant given the spread of antibiotic-resistant strains of pathogenic bacteria. Both natural and genetically modified bacteriophages are used to treat antibiotic-resistant infections. Scientists have recently succeeded in synthesizing a bacteriophage from scratch.

Bacteriophage genomes are small, but the functions of far from all phage genes are currently known. It's possible that sequences with unknown functions (and they constitute up to 80% of the genome!) could pose challenges when using phages in humans. Furthermore, they complicate the process of genetically modifying phages. Portuguese scientists decided to create a lytic bacteriophage with a minimal genome—containing only the genes necessary for infecting a specific target bacterium and completing its full replication cycle. A similar experiment had previously been conducted on prokaryotes: the scientists created the bacterium Mycoplasma mycoides with a minimal genome.

A new synthetic bacteriophage targets Pseudomonas aeruginosa , a bacterium known for the widespread occurrence of antibiotic-resistant strains. Treatment of Pseudomonas aeruginosa infections is a WHO priority. The scientists used a bacteriophage specific to P. aeruginosa , isolated from wastewater (called PE3). Of 28 P. aeruginosa samples obtained from patients, the bacteriophage infected seven. The PE3 genome was sequenced and found to contain a predicted 55 protein-coding sequences.

Scientists excised several gene blocks from the bacteriophage PE3 genome, propagated the resulting constructs in yeast cells, and then transferred them to the host bacterium P. aeruginosa to test whether the phage's genetic information was capable of activating the viral particle assembly program. The experiment was successful: visible phage plaques formed in the bacterial cultures—sites where the virus had destroyed the bacteria.

Further experiments revealed some peculiarities of the synthetic phages: not all synthetic bacteriophages were able to infect the same strains of Pseudomonas aeruginosa as their natural predecessor; the antibacterial efficacy of the bacteriophages in vitro remained high; in vivo experiments on insects (the greater wax moth G. mellonella), synthetic bacteriophages, like their natural predecessor, increased the survival rate of animals infected with P. aeruginosa.

The authors of the study believe that their approach to creating synthetic phages will allow for the rapid creation of lytic bacteriophages against specific pathogenic bacteria in the future.

* Pires DP, Monteiro R., Mil-Homens D. et al. Designing P. aeruginosa synthetic phages with reduced genomes. Sci Rep; 2021, 11:2164. https://doi.org/10.1038/s41598-021-81580-2