For microalgae, the microscopic organisms photosynthesizing in the ocean, nitrogen is crucial in regulating metabolism. When nitrogen levels dip, their cells don't divide efficiently and they can't photosynthesize as well as when nitrogen is not limited. So how do microalgae continue to thrive even though the majority of oceanic surface waters are nitrogen-deficient?

In a recent paper published in PNAS, researchers found that the ability of microalgae to persist in both nitrogen-poor and nitrogen-fluctuating environments is thanks to the nucleic acid guanine. Guanine is the "G" in DNA, and is also a nitrogen-containing metabolite used for all kinds of cellular purposes. It is widely available in nature from sources such as decomposing fish tissues and scales.  

This new research found that diverse microalgae, including freshwater and marine algae as well as those present in reef-building corals, all contain long-term nitrogen reserves in the form of crystalline guanine. 

Using fluorescence and transmission electron microscopy, researchers found that for one marine single-celled alga Amphidinium carterae, the storage capacity for crystalline guanine was enough to support nitrogen requirements for several new generations. By using guanine as a storage form for nitrogen, microalgae can protect themselves from the potential harms of nitrogen shortage.