Fig. 6: Potential contribution of viruses to nitrogen cycling and transport.
From: Potential virus-mediated nitrogen cycling in oxygen-depleted oceanic waters
The schematic represents the main pathways that drive the nitrogen cycle and the participating enzymes and transporters. Proteins with a viral version are highlighted in orange boxes. Viral NorB and NOD correspond to the same protein that is homologous to both nitric oxide reductase and nitric oxide dismutase. Nitrogen uptake is performed by the ammonia transporter (AmtB, which is regulated by PII), the MFS-type nitrate/nitrite transporter (Nrt), the ABC-type nitrate transporter (NrtABCD), and the formate/nitrite transporter (FocA). The enzymes that transform nitrogen are molybdenum-iron nitrogenase (NifHDK), iron-iron nitrogenase (AnfHGDK), vanadium-iron nitrogenase (VnfHGDK), an ammonia monooxygenase (AmoCAB), hydroxylamine dehydrogenase (Hao), nitrite oxidoreductase (NxrAB), ferredoxin-nitrate reductase (NarB), nitrate reductase (NAD(P)H) (NR), assimilatory nitrate reductase (NasAB), ferredoxin-nitrite reductase (NirA), nitrite reductase (NAD(P)H) (NIT-6), membrane-bound nitrate reductase (NarGHI), periplasmic nitrate reductase (NapAB), nitrite reductase (NADH) (NirBD), cytochrome c nitrite reductase (NnfAH), copper-containing nitrite reductase (NirK), heme-containing nitrite reductase (NirS), nitric oxide reductase (NorBC), nitrous oxide reductase (NosZ), hydrazine synthase (HzsCBA), hydrazine dehydrogenase (Hdh), and nitric oxide dismutase (NOD).
