All cyanobacteria have the ability to fix carbon from the atmosphere, stuffing it away in starch or glycogen, but Cyanothece is among the rarer strains that can also fix nitrogen, converting atmospheric nitrogen to ammonia and eventually to larger nitrogen-rich molecules.
Because it can fix both carbon and nitrogen, when conditions warrant Cyanothece can survive on air, water and sunlight alone. It is about as self-reliant an organism as it is possible to be.
There is one catch. Nitrogenase is very sensitive to oxygen and so carbon fixing (photosynthesis), which produces oxygen as a byproduct, has to separated from nitrogen-fixing in some way.
Cyanothece accomplishes this by time division; it has an internal biological clock that establishes a circadian rhythm. (Cyanobacteria are the only prokaryotes (organisms without nuclei) that have a clock.)
So Cyanothece fixes carbon glycogen molecules during the day, producing oxygen as a byproduct, and it fixes nitrogen in ammonia during the night, producing hydrogen as a byproduct. For every nitrogen molecule that's fixed, says Pakrasi, one hydrogen molecule is produced.
Each half of the cycle powers the other. The glycogen produced in the day is consumed in the energy intensive process of fixing nitrogen at night. The fixed nitrogen produced at night is used to make nitrogen-containing proteins during the day.
Pakrasi, who is also the director of I-CARES, the International Center for Advanced Renewable Energy and Sustainability, calls the microbes biobatteries because they store daytime energy for use at night and nighttime energy for use in the day.
The separation in time prevents the two metabolic processes from competing with one another. At night the bacteria begin to metabolize the glycogen (or respire).
Quickly consuming intracellular
|Contact: Diana Lutz|
Washington University in St. Louis