Nostoc commune var sphaeoroides
by Jack Darcy
Every living thing needs it, but nitrogen (N) is tough to get in nature. On earth our primary source of N is the air, which is 80% N. But atmospheric N is very difficult for living things to use, because it consists of two N atoms triple-bonded together. Getting them apart, so they can be bonded to other atoms, requires a LOT of energy. Fortunately, Cyanobacteria of the genus Nostoc are famous worldwide for their ability to convert atmospheric N into a biologically useful form. Although other microbes can do this “N-fixing” too, these photosynthetic bacteria are special because they fix N, they fix C (they turn atmospheric carbon dioxide into their food!), and they are really cool-looking.
Some of these Nostoc grow as spherical colonies (see picture), which are eaten by people in Peru and Chile. We call these strains Nostoc commune var. sphaeroides, but in Peru they are called “algas de la laguna”, “cushuro”, and “llullucho”. The edible forms of these cyanobacteria are commonly found in streams, but their close relatives have been found in much more extreme environments. In our expeditions to the Peruvian Andes, we’ve found tiny (less than 1mm in diameter) Nostoc spheres in dry, plant-free soil that was recently uncovered by a retreating glacier (Darcy et al. 2018).
We also found related Nostoc species at extremely high-elevation, above 5500 meters above sea level (18,100 feet), where the air is very cold, it’s very dry, and only the toughest microbes can survive (Schmidt et al. 2017).