## 4 AMGs with the Potential to Impact Central Carbon Metabolism
Through metagenomics analysis, the glycogen biosynthetic gene encoded by the _glgA_ gene was identified from the viromes isolated from the Pacific Ocean [86]. The _glgA_ gene-encoded enzyme catalyzes the conversion of G6P to glycogen, suggesting that virus infection may induce a starvation response in the host and direct more carbon flux to the glycolysis pathway [87]. The mannose-6-phosphate isomerase, encoded by _manA_ and involved in mannose metabolism, was also identified [86]. Mannose-6-phosphate isomerase is known to convert M6P to F6P for use in glycolysis [88] (Scheme 2A). Global warming has considerable implications for aquatic ecosystems, triggering various changes. With rising water temperature, dissolved oxygen levels can drop, and changes in both pH and salinity can occur [89]. These changes directly impact cyanobacteria, with rising temperatures and CO\({}_{2}\) levels likely to promote cyanobacterial blooms [90]. There is potential for these blooms to, once again, bring balance, restoring depleted oxygen levels, and to an extent, provide a screen, shading the underlying water from direct sunlight. However, these blooms are limited by nutrient availability. Increasing cyanobacterial levels are likely to result in increased populations of phages. Lysis caused by phage infection results in the re-release of limiting nutrients, enabling the cycle to continue and possibly enabling the further restoration of restored oxygen. **Scheme 2. ** AMGs involved in central carbon metabolism. **(A)** Cyanophage genes involved in the Calvin-Benson cycle and pentose phosphate pathway. After infection, the expression of cyanophage gene \(cp12\) can inhibit the Calvin cycle and carbon fixation. The expression of cyanophage genes _talC_, _zwf_, and _gnd_ can enhance the PPP. Pi, phosphate; CbbA, fructose-1,6-bis P/sedoheptulose-1,7-bis-P aldolase; GlpX, fructose-1,6/sedoheptulose-1,7-bisphosphatase; Pgi, P-glucose isomerase; Pgk, P-glycerate kinase; Pgi, 6-P-gluconolactone; PrkB, P-ribulokinase; RbCLS, ribulose-1,5-bis-P carboxy-lase/oxygenase; Rpe, ribulose-5-P epimerase; RpiA, ribulose-5-P isomerase; TktA, transketolase; Tpi, triose-P isomerase; BPG, 2,3-bis-P-glycerate; DHAP, DHA P; E4P, erythrose 4-P; FBP, fructose 1,6-bisP; F6P, fructose 6-P; GAP, glyceraldehyde3-P; G6P, glucose 6-P; PGA, 3-P-glyceric acid; R5P, ribose 5-P; RuBP, ribulose 1,5-bis-P; RuSP, ribulose 5-P; SBP, sedoheptulose 1,7-bis-P; GPG, 6-P-gluconolate; 6 PGL, 6-P-gluconolactone; S7P, sedoheptulose 7-P; and XSP, xylulose 5-P. **(B)** Cyanophage genes involved in L-cysteine biosynthesis (Purple), Tricarboxylic acid (TCA) cycle (Red), glyoxylate shunt (Blue), and 3-hydroxypropionate (Green). The genes (\(\sim\)3-fold) of the TCA cycle were those involved in the glyoxylate shunt. The glyoxylate shunt was used to increase the cellular reducing power and ATP for phage synthesis. **(C)** Cyanophage genes involved in the adenosylcobalamin (cofactor B12) biosynthesis pathway. In a recent study, the transcription levels of SLC13 permease, sulfate adenylyl-transferase, adenylyl-sulfate kinase, phosphoadenosine phosphosulfate reductase, assimilatory sulfite reductase, and cysteine synthase A \(O\)-acetylserine sulfhydrylylase were increased after infection of _Pseudoalteromonas_ by cyanophage HP1. These genes are involved in the assimilatory sulfate reduction pathway and the L-cysteine biosynthesis pathway (Scheme 2B) [91; 92]. Researchers posited that the synthesis of cysteine in infected cells provided more energy because cysteine can be degraded to acetyl-CoA for energy production in the TCA cycle [93]. From the Pacific Ocean Virome dataset, components of the TCA cycle have been identified including acontase (_acn_), isocurate dehydrogenase (_icd_), 2-oxoglutate dehydrogenase (_sucABCD_), isocurate lyase, succinate dehydrogenase (_sdh_), and fumarate hydratase (_fum_). Malate synthase A (_aceAB_), involved in the glyoxylate shunt, was also identified [86].