Ocean Bacteria Recycles Iron
In the vast ocean where an essential nutrient — iron — is scarce, a marine bacterium that launches the ocean food web survives by using a remarkable biochemical trick: It recycles iron.
By day, it uses iron in enzymes for photosynthesis to make carbohydrates; then by night, it appears to reuse the same iron in different enzymes to produce organic nitrogen for proteins.
The bacterium, Crocosphaera watsonii, is one of the few marine microbes that can convert nitrogen gas into organic nitrogen, which (just as it does on land) acts as fertilizer to stimulate plant growth in the ocean. So the ocean’s productivity is limited by nitrogen, which in turn is limited by scanty supplies of iron for the enzymes needed to make organic nitrogen.