## 2 Overview of Cyanphage
In addition to genes encoding the assembly of new cyanophage genes relating to enhancing photosynthesis that dominate, genes relating to central carbon metabolism, phosphate metabolism, methylation, and regulation are prevalent. Genes with sequence similarity to known halogenases are also abundant. This global analysis and distribution of the AMGs are presented in Figure 2. The AMGs and their potential role as the cyanophage infects the host cyanobacterium are reviewed in the following sections. After infection, cyanophage AMGs are expressed, impacting photosynthesis, carbon metabolism, phosphate metabolism, and regulation. The resulting energy and flux of precursors are redirected toward phage DNA synthesis and capsid production. The counterparts of numerous AMGs linked to photosynthesis and central carbon metabolism may be seen in the genomes of myocyanophages. This is undoubtedly their origin. As shown above (Figure 1A), myocyanophages generally have considerably larger genomes than the other cyanophages and possess a long contractile tail enabling the delivery of this much larger genome into bacteria. This tail is sheathed and operates via a contractile mechanism, resulting in the highly efficient injection of its DNA into the host. As a result of housing a much larger genome, the heads of myocyanophages are larger than those of other cyanophages. This larger casing, more sophisticated injection machinery, in combination with the much larger genome, places a greater metabolic burden on the host. Correspondingly, almost all of the myocyanophages can be seen to carry multiple AMGs that potentially force the upregulation of photosynthesis to sequester further carbon and the upregulation of carbon metabolism to generate the substantial additional energy needed. Curiously, two exceptions emerge: _Synechococcus_ phage-S-H34, (Figure 2, entry 88), an outlier in terms of its much higher GC content, appears not to have any AMGs related to photosynthesis. _Synechococcus_ phage-BUCT-ZZ01 (Figure 2, entry 84), one of the smaller myocyanophage, appears to not have any AMGs related to glycolysis. The availability of phosphate is essential to the generation of new DNA as the phage replicates. So far, the myocyanophage alone may be seen to possess AMGs linked to the modulation of phosphate metabolism. It is puzzling that one of the larger myocyanophages, _Synechococcus_ phage-ACG-2014f, does not have any AMGs related to phosphate metabolism (Figure 2, entry 96). Figure 1: Genomic and phylogenetic features of cyanophage families. (**A**) Scatterplot of the GC (guanine-cytosine) content and genome size. (**B**) Phylogenetic: ML tree with related cyanophages based on the nucleotide sequences of DNA polymerase and terminase. The trees were constructed in MEGA version 7 by the ML method. Figure 2: Widespread distribution of AMGs related to photosynthesis and carbon metabolism across the 153 cyanophage AMGs labelled I–XLV and cyanophages labelled 1–151. **AMGs involved in photosynthesis and carbon metabolism**. **I**. Photosystem **II** reaction center protein PsbA/D1, **II**. Photosystem II D2 protein, **III**. 2 OG-Fe (II) oxygenase family oxidoreductase, **IV**. Phycocyanophilic: ferredoxin oxidoreductase (PcyA), **V**. Ferredoxin (PetF), **VI**. Phycerythrobilin lyase (CpeT), **VII**. Phycerythrobilin synthase (PebS), **VIII**. Phycerythrobilin, **IX**. NADH dehydrogenase subunit I, **X**. NAD synthetase, **XI**. Plastoquinol terminal oxidase PtoX. **XII**. Plastocyanin (PetE), **XIII**. Hem oxygenase (HO), **XIV**. Hli gene family/high-light inducible protein, **XV**. Thioredoxin, **XVI**. RfaE bifunctional protein, **XVII**. Transaldolase family protein (TaLc) in this family, **XVIII**. Glucose 6-phosphate dehydrogenase Zwf, **XIX**. 6-phosphogluconate dehydrogenase Gnd, **XX**. FAD-dependent thymidylate synthase/thymidylate synthase, **XXI**. Chorbylesterase, **XXII**. UDP-glucose 6-dehydrogenase, **XXIII**. Acyl carrier protein ACP, **XXIV**. Fructose-6-phosphate aldolase, **XXV**. Phage host specificity protein, **XXVI**.