# A Novel Singleton Giant Phage Yong-XC31 Lytic to the _Pyropia_ Pathogen _Vibrio mediterranean_
## 4 Discussion
An even more radical strategy is used by some giant phage, not need to rely on the host RNAP, yet only relies on self-encoded phage multi-subunit RNAPs: virion-associated RNAPs and early expressed RNAPs [14]. These RNAPs can perform two functions. The virion-associated RNAP is injected into the host cell together with phage DNA and transcribes early phage genes [53]. The early expressed RNAP formed by putative RNAP subunits which would transcribe viral genes expressed in the middle and late stages of infection [54]. This study finds that Yong-XC31 contains five genes encoding virion-associated RNAPs (ORF34, ORF136, ORF140, ORF142, ORF153) and three early expressed RNAPs (ORF46, ORF47, ORF69). This may be beneficial to its efficient infection. In addition, the absence of detectable tRNA in phage BONAISHI genome suggests that it is well adapted to the translation machinery of its hosts, which is a critical process for efficient phage propagation [50]. Similarly, we did not find any tRNA in the genome of Yong-XC31. As mentioned above, alternative therapies must be developed to mitigate the sharp increase in antibiotic resistance. Besides phage itself, novel antimicrobial strategies include enzyme-based antibiotics (\"enzybiotics\") such as phage lytic enzymes. Yong-XC31 harbors multiple (at least eight) enzyme genes related to bacteriolysis. These enzyme genes may be potential beneficial resources. Very little is known about the processes of host-phage interaction in marine environments. [PERSON] et al., found that _Synechococcus_ phage S-PM2 contain genes encode homologs of the key photosystem II reaction center core polypeptides (D1 and D2) and proposed that this might play an active role in protecting their hosts against photoinhibition, thereby ensuring an energy supply for replication by preventing the deleterious effects on host cell integrity seen during acute photoinhibition [55]. Phages infecting marine picocyanobacteria often carry a _psbA_ gene, which encodes a homolog to the photosynthetic reaction center protein, D1. [PERSON] et al., proposed that phage encoded D1 may help to maintain photosynthesis during the lytic cycle, which in turn could bolster the production of deoxynucleoside triphosphates (dNTPs) for phage genome replication [56]. They examined the contribution of phage _psbA_ expression to phage genome replication under constant low irradiance and predicted that phage _psbA_ expression could lead to an increase in the number of phage genomes produced during a lytic cycle of between 2.5 and 4.5% [56]. In this study, Yong-XC31 possesses unusual genes rarely present in other phages. In particular, Yong-XC31 contains an ORF encoding Methyl-accepting chemotaxis protein (MCP) and a gene encoding EIIB belonging phosphotransferase system. As the predominant chemoreceptor and signal transducer in bacteria and archaea, MCPs also termed transducer-like proteins (Tlps), serve as sensors in bacterial chemotactic signaling [57]. MCPs sense intracellular and environmental signals, and relay them to the downstream signaling pathways in the cytoplasm. Then, bacteria utilize the well-known chemotactic responses to move towards factors that favor survival [58]. Further studies are needed to find whether the expression of the viral methyl-accepting chemotaxis protein gene may enhance the host survival and persistence in the complex environment, thus profiting the phage itself. The phosphoenol phosphotransferase system (PTS) is a multi-component signal transduction cascade that regulates diverse aspects of bacterial cellular physiology in response to the availability of high-energy sugars in the environment [59]. In bacteria, there are often many different EIIs. EIIs are responsible for the phosphorylation of the carbohydrate as well as its transportation across the bacterial membrane [60]. The significance of gene encoding EIIB in Yong-XC31 remains to be studied.