Chlamydomonas Reinhardtii - Clean Source of Hydrogen Production

Clean Source of Hydrogen Production

In 1939 the German researcher Hans Gaffron (1902–1979), who was at that time attached to the University of Chicago, discovered the hydrogen metabolism of unicellular green algae. Chlamydomonas reinhardtii and some other green algae can, under specified circumstances, stop producing oxygen and convert instead to the production of hydrogen. This reaction by hydrogenase, an enzyme only active in the absence of oxygen, is short-lived. Over the next thirty years Gaffron and his team worked out the basic mechanics of this photosynthetic hydrogen production by algae.

To increase the production of hydrogen, several tracks are being followed by the researchers.

• The first track is decoupling hydrogenase from photosynthesis. This way, oxygen accumulation can no longer inhibit the production of hydrogen. And, if one goes one step further by changing the structure of the enzyme hydrogenase, it becomes possible to render hydrogenase insensitive to oxygen. This makes a continuous production of hydrogen possible. The flux of electrons needed for this production comes, in this case, no longer from the production of sugars, but is drawn from the breakdown of its own stock of starch.
• A second track is to interrupt temporarily, through genetic manipulation of hydrogenase, the photosynthesis process. This inhibits oxygen reaching a level where it is able to stop the production of hydrogen.
• The third track, mainly investigated by researchers in the 1950's, is chemical or mechanical methods of removal of O2 produced by the photosynthetic activity of the algal cells. These have included the addition of O2 scavengers, the use of added reductants, and purging the cultures with inert gases. However, these methods are not inexpensively scalable, and may not be applicable to applied systems. However, some new research has appeared on the subject of removing oxygen from algae cultures, and may eliminate scaling problems.