ABSTRACT
Natural photosynthesis in green plants achieves carbon dioxide fixation on a global scale. However, the efficiency of solar energy conversion in plant production under optimal growth conditions is only 5 to 6%. Under field conditions, even high-yielding crops (such as maize, bulrush millet, or sugarcane) convert solar energy into plant material with a maximal efficiency of 1 to 2%. Most major crops and forests achieve much lower efficiencies. The global average efficiency has been estimated as 0.15%.^ There exist thus considerable interest in other non photosynthetic pathways for carbon dioxide fixation. One of these is that per formed by the bacterial methanogens.^’^
BACTERIAL METHANOGENS
Non-photosynthetic carbon dioxide fixation occurs widely in nature — by methanogenic bacteria. These are obligate anaerobes, growing in freshwater and marine sediments, in peats, the gut of animals, sewage sludge, and manure piles.
