Reverse Photosynthesis: Degradation of Biomass by Sunlight

The activity of cellulose degrading enzymes can have increased efficiency of clean processes in biotechnology

DENMARK – Plants, algae and some bacteria use solar radiation as an energy source for biochemical reactions in the construction of biomass.  Through the process of photosynthesis, carbon dioxide, water and sugar molecules are generated, which are then converted, into long-chain carbohydrates such as starch and cellulose.

Danish biotechnologists from the University of Copenhagen have now discovered that the solar energy can also enhance a reaction in the opposite direction.  The absorption of light by chlorophyll can transfer energy to certain enzymes that cleave cellulose, under oxygen consumption, into smaller fragments.

Using this “reverse photosynthesis” it could be possible to produce biofuels from plant material such as straw or wood in an environmental friendly manner.

“This discovery could change the industrial production of fuels and chemicals fundamentally and thus reduce pollution considerably,” says Claus Felby of the University of Copenhagen.  His research team examined the degradation of cellulose by special monooxygenases. The oxidizing enzymes can be found in high activity in fungi that destroy plant cell walls.  Monooxygenases are already being used in purified form in industrial processes for the biomass utilization.

The researchers used a ventilated oxygen mixture of cellulose, monooxygenases and ascorbic chlorophyll of cyanobacteria or plants and irradiated the reaction with sunlight. Thereby, the enzyme activity increased a hundredfold.  It proved to be particularly effective in further experiments where the blue and red portion of the light spectrum was absorbed by the chlorophyll.

Also hemicellulose, another main component of plant cell walls, has been highly efficiently degraded in this way – without additional energy consumption and without producing pollution.

Industries can use the reaction chemical as fuels or as starting materials for the production of plastics such as ethanol and methanol.

The importance of the “reverse photosynthesis” to the natural global carbon cycle is yet to be studied.

This research study was published in journal “Nature Communications”.

Source:  Faculty of Science – University of Copenhagen

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