Background Information

As the world looks for alternative and environmentally friendly fuels it has gone in many directions, one of them being algae for bio-fuels. Algae have mostly been looked at as a way to produce bio-diesel and now hydrogen. Generating hydrogen via photosynthetic organisms is a way to produce hydrogen in an environmentally friendly and eventually economical way. Since most other methods of producing hydrogen can cause a lot of pollution and use a lot of energy; the use of algae can be seen as a feasible solution.

Photosynthesis

Photosynthetic organisms are organisms that use sunlight, carbon dioxide and water to create sugar which is used in cellular respiration to create ATP, the fuel used by living things. Algae are photosynthetic and therefore use sunlight to create for themselves energy while fixating CO2 from the air. During regular photosynthesis they also release oxygen as a product. However, it has been found that an algae, called Chlamydomonas reinhardtii, under certain conditions have the ability to produce hydrogen.

Sulphur Depletion

There are two methods that are known to be able to make Chlamydomonas reinhardtii switch into producing hydrogen. One is depriving them of sulphur and the other is by adding copper. Depriving the algae of sulphur leads to photosynthesis shutting down in the cells. This occurs because sulphur is a valuable nutrient and is used in producing amino acids required to make enzymes that allow photosynthesis to occur. Because these enzymes can no longer be produced properly do to the disruption of certain amino acids, photosynthesis cannot be carried out. Once the plants stop to photosynthesize they use up the oxygen within the closed environment through cellular respiration. Once the environment around it is anaerobic hydrogenase can now function and produce hydrogen gas.

Addition of Copper

The addition of copper works on the same basis as depriving of sulphur. By adding copper to the algae’s environment their ability to produce oxygen is stopped. Copper hinders the ability of the algae to do photosynthesis properly by preventing photosystem II synthesis (which generates oxygen) to function. This happens because the copper ions disrupt the function of a gene (the Nac2 gene) required for photosystem II synthesis. This means if the algae cannot produce oxygen and are in an enclosed environment, the environment will eventually become anaerobic due to cellular respiration. Once this has occurred the algae can synthesis hydrogenase, which allows an alternate route to produce energy. Hydrogenase produces hydrogen gas as a product of its reaction (this reaction still requires light).

Chlamydomonas reinhardtii

Chlamydomonas Reinhardtii algae are unicellular flagellates (with two flagellums) and are part of the Chlorophyta genus. These algae are normally found in soil and freshwater. They have a large chloroplast, a cell wall, two flagella and a large pyrenoid (“eyespot”) which is used to sense light. Cells of the Chlamydomonas Reinhardtii species are haploid cells and can be grown in a simple salts medium with sunlight for photosynthesis.