The Air You Breathe, the Food You Eat

Cyanobacteria, a kind of blue-green algae, live in water, manufacture their own food, and, during the Archaean Age, were responsible for creating the oxygen we breathe.

If you were able to travel back 3.5 billion years to the Archaean period in the earth’s history, you would think you were in hell. The atmosphere was made up of methane, ammonia, and other gases toxic to most life on our planet today. And then along came the cyanobacteria. They turned hell into the Garden of Eden.

Cyanobacteria are busy little buggers and it’s a good thing for us that they are. In addition to creating the air we breathe, proterozoic oil deposits can be attributed to the activity of cyanobacteria, and they are also important providers of nitrogen fertilizer in the cultivation of rice and beans. The other great contribution of the cyanobacteria is the origin of plants. The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells.

Cyanobacteria are one of very few groups of organisms that can convert inert atmospheric nitrogen into an organic form, such as nitrate or ammonia, which plants need for their growth, and must obtain from the soil. Fertilizers work the way they do in part because they contain additional fixed nitrogen which plants can then absorb through their roots.

Interestingly, many plants, especially legumes, have formed symbiotic relations with nitrifying bacteria, providing specialized tissues in their roots or stems to house the bacteria, in return for organic nitrogen. This has been used to great advantage in the cultivation of rice, where the floating fern Azolla is actively distributed among the rice paddies. The fern houses colonies of the cyanobacterium Anabaena in its leaves, where it fixes nitrogen. The ferns then provide an inexpensive natural fertilizer and nitrogen source for the rice plants when they die at the end of the season. Azolla has been used as a green manure crop in Vietnam and China for centuries.

Like so many other aspects of our earth’s ecosystem, cyanobacteria work their wonders in relative anonymity. One can only hope that we humans come to understand Mother Earth well enough to appreciate and preserve her essential life processes. Live long and prosper, little cyano!