# Genomic Characterization of a Halovirus Representing a Novel Siphoviral Cluster
## 4 Discussion  
Viruses are thought to be the most abundant biological entities on Earth; however, very few have been cultivated. There remain numerous viruses that have yet to be recognized. In this study, we isolated a new siphovirus, YPHTV-1, infecting _H. titanica_ H5, from salt mine samples stored at room temperature for 10 years. YPHTV-1 was very stable at room temperature and in a hypersaline environment, and its genome contained genes that may promote the host's resistance to stress. YPHTV-1 had a high specificity for the host, which has also been observed in the halovirus CG\(\Phi\)29 [22]. The first step of phage infection is recognition and adsorption. Bacteria can prevent phage attachment by lacking or hiding surface receptors. Even if phages attach to appropriate surface receptors successfully, a superinfection rejection system and other mechanisms can prevent phage DNA from being injected into host cells [59]. After a phage has injected its DNA into bacterial cells, the natural defense system in the host cells can also prevent phage proliferation, such as abortive infection and restriction modification systems that can cause the host to cut or degrade phage DNA before releasing the progeny virus, preventing phage replication and release [60]. These influencing factors also determine the host range of phages. The inability of the phage YPHTV-1 to infect the H5G was caused by the steps after adsorption. To date, genome sequencing has been completed for two viruses infecting _Halomonas_ sp., i.e., the myoviral phage \(\Phi\)HAP-1 induced by mitomycin C from the surface water of the Gulf of Mexico [20] and the siphoviral phage QHHSV-1 isolated from Qiaohou Salt Mine in China [25]. These three _Halomonas_ phages have similar genome sizes (37,270-39,245 bp). The phage YPHTV-1 has the lowest GC content among the three _Halomonas_ phages (36.2% (YPHTV-1) vs. 59% (\(\Phi\)HAP-1) and 66.8% (QHHSV-1)). One mechanism by which phages alter the metabolic state of the host is through the activity of phage-encoded AMGs [61; 62]. AMGs are typically obtained from host cells (i.e., recombined onto phage genomes) and can enhance or redirect specific metabolic processes within host cells during infection [63; 64]. These enhancements may play an important role in maintaining, driving, or shortening the metabolic pathways and may provide phages and their hosts with sufficient fitness advantages to retaining these genes over time under specific metabolic or nutritional conditions [65]. Many AMGs were predicted in the YPHTV-1 genome, and their functions involved radiation resistance (\(\mathit{ImmA/IrrE}\) family metalloendopeptidase), antibiotic resistance (MBL folding metallohydrolase), regulation of osmotic pressure (O antigen ligase), and response to starvation (MazG-like family protein). [PERSON] et al. have found that ImmA/IrrE was required for _Deinococcus_ resistance to ionizing radiation, ultraviolet light, and mitomycin C as a global transcriptional regulator [51]. The MBL folding metallohydrolase can be combined with cysteine, histidine, aspartic acid, and other active sites of amino acids and zinc and then combined with water molecules for activation, after which it becomes a nucleophile, with a wide range of hydrolysis effects on \(\beta\)-lactam antibiotics, leading to resistance to cephalosporins, carbapenemems, and other antibiotics and playing an important role in the bacterial carbon-phosphorus lyase (CP-Lyase) pathway [53]. The O antigen ligase connection of O antigen to the core region of the lipid A core is an important step in the LPS biosynthetic pathway. O antigen ligase and acyltransferase participate in the synthesis of LSP to protect the host from other bacteria or viruses, which can change the cell membrane permeability, increase tolerance to high osmotic pressure, cause adaptation to hypersaline environments, and increase antibiotic resistance, improving the ability of the host to adapt to extreme environments [66]. MazG is considered a regulator of programmed cell death in _E. coli_.