# A Novel Benthic Phage Infecting _Shewanella_ with Strong Replication Ability
## 3 Results and Discussion
### Genomic Features of the Phage S0112
MazG was implicated as a regulator of programmed cell death in _Escherichia coli_ by interfering with the MazEF toxin-antitoxin system through reducing the intracellular guanosine 3',5'-bispyrophosph (ppGpp) levels. The small nucleotide ppGpp, as a global regulator of gene expression, whose accumulation can cause the reorientation of bacterial transcription, and only genes important for starvation survival can be expressed [50; 51]. Given the role of MazG in _E. coli_, it was proposed that phages containing _mazG_ gene may trick the host to mimic a nutrient replete cell state by reducing the accumulation of ppGpp in the host cells, so that phages can utilize the host RNA transcription system to amplify the progeny phages [52]. However, a recent study found that the purified MazG from cyanophage has no binding or hydrolysis activity to ppGpp [49]. Instead, cyanophage encoded MazG protein can bind and hydrolyze dGTP and dCTP deoxyribonucleotides, and it was speculated that it may indirectly regulate the host stringent response by hydrolyzing other nucleotide substrates [49]. Here, the specific function of MazG gene in the phage S0112 remains to be studied. Another feature of phage S0112 is the presence of a gene cluster consisting of five functional genes encoding QueC (7-cyano-7-deazaguanine synthase), QueD (6-carboxy-5,6,7,8-tetrahydroopterins synthase), FolE (GTP cyclohydrolase I), queuosine tRNA-ribosyltransferase, and organic radical activating enzyme. This kind of gene cluster has also been observed in other phages, such as _Rhizobium_ phage RHEph04 [53], RSC [54], _Vibrio_ phage VpKK5 [18], _Escherichia coli_ phage 9g [55], and the genus _Seuratvirus_[56]. This gene cluster involves in the biosynthesis of a precursor, i.e., 7-cyano-7-deazaguanine (preQ\({}_{0}\)), of queuosine or archaeosine [57]. Queuosine is a well-known nucleoside derivative that modifies tRNAs by replacement of guanine at certain position [58]. Queuosine modification in bacteria was considered a way to improve reading frame maintenance [59], but this opinion is still controversial, as a recent study did not observe this function in _Escherichia coli_[60]. Meanwhile, a phage infecting _Escherichia coli_ that contains homologues of queuosine biosynthesis genes, including organic radical activating enzyme, queuosine tRNA-ribosyltransferase, QueC, QueD, FolE, and (GAT)-QueC (glutamine amidotransferase class-II) was found to be resistant to a wide range of restriction endonucleases, by modifying its DNA (converting deoxyguanosine to 2'-deoxy-archaeosine) [55; 56; 57]. As reported, phages belonging to the genus _Seuratvirus_ contain QueC, QueD, and QueE, as well as FolE, modify their DNA with queuosine, as they lack homologues of (GAT)-QueC, which is required for the insertion of archaeosine [56]. Our analysis showed that phage S0112 contains only QueC homologues without the homologues of (GAT)-QueC, and we propose that phage S0112 may modify their DNA in a similar manner to the genus _Seuratvirus_. Further work is needed to verify the biological role of the queuosine biosynthesis genes in phage S0112.