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Hydrogen Gas Using Nitrogenase.

In cyanobacteria (blue green algae), ‘nitrogenase’ enzyme is the chief hydrogen producing enzyme.

This is considered better, because hydrogenase enzyme is sensitive to oxygen which is produced during the photolysis of water, while nitrogenase enzyme is relatively less sensitive to oxygen.

Further, in the heterocysts of cyanobacteria, oxygen concentration is low or completely absent, so that hydrogen production becomes more efficient.

The enzyme nitrogenase reduces nitrogen to NH3 with associated release of hydrogen gas.

Hydrogen evolution depends on light, which provides electron donors and also activates nitrogenase and ATP formation in heterocysts. It has been shown that light dependent hydrogen evolution can continue for several days in some strains of Anabaena (nitrogen fixing cyanobacteria).

Hydrogen production. Hydrocarbons produced by some microorganisms may also serve as liquid or gaseous fuels. For instance, microbial production of methane gas from polymers like carbohydrates, proteins, lipids, etc.

Involves following three steps : (i) breakdown of polymers into organic acids and alcohols by hydrolytic and fermentation bacteria;

(ii) conversion of acids and alcohols into acetates, H2 and CO2 by the hydrogen producing acetogenic bacteria  and

(iii) conversion of acetate and H2 + CO2 to methane by methanogenic bacteria.

Hydrocarbons are also produced by unicellular alga Botryococcus braunii, which possesses a hydrocarbon content as high as 75% of its dry weight, the highest reported in any kind of biomass.

Therefore, cultivation of this alga offers a direct and renewable source of ‘solar fuel’. Several other algae and fungi are also involved in the production of hydrocarbons and, therefore, can be used to produce hydrocarbons as a source of energy.

 
   
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