1.E.67.  The Holin of Pseudomonas phage HZ2201 (HolinPP) Family 

Pseudomonas aeruginosa is a clinically common conditionally pathogenic bacterium, and the abuse of antibiotics has exacerbated its drug resistance. This has resulted in extensive reports about the usage of Pseudomonas aeruginosa phage as a novel antibacterial drug. Fei et al. 2023 isolated a novel phage HZ2201 with a broad lytic spectrum. The lytic rate of this phage against P. aeruginosa reached 78.38% (29/37), including 25 multi-drug- and carbapenem-resistant P. aeruginosa strains. Transmission electron microscopy revealed that phage HZ2201 belongs to the class Caudoviricetes. Biological characterization showed that phage HZ2201 had an latent period of 40 min, a lytic period of 20 min, and a burst size of 440 PFU/cell, with improved tolerance to temperature and pH. Considering genomic analysis, the HZ2201 genome was a circular double-stranded DNA with a size of 45,431 bp and a guanine-cytosine (G + C) content of 52.16%, and contained 3 tRNAs. 27 of the 74 open reading frames (ORFs) annotated by the Rapid Annotation using Subsystem Technology (RAST) tool could be matched to the genomes of known functions, and no genes related to virulence and antibiotic resistance were found. The phylogenetic tree suggests that phage HZ2201 is highly related to the phage ZCPS1 and PaP3, and ORF57 and ORF17 are predicted to encode a holin and an endolysin, respectively. Cell lysis by HZ2201 proceeds through the holin-endolysin system, suggesting that it is a novel phage. Additionally, phage HZ2201 has a high inhibitory capacity against P. aeruginosa biofilms. The results of our study suggest that phage HZ2201 is a novel potential antimicrobial agent for treating drug-resistant P. aeruginosa infections (Fei et al. 2023 ).