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Brown algae being engineered for food and bio-ethanol
December 2, 2013
uropean Biotechnology News reports that researchers, together with Norwegian and Chilean bioethanol producers, have developed advanced techniques to produce food and bio-ethanol from brown algae, which does not require arable land, fresh water or fertilizers.
Until now, cultivation of that feedstock was not sustainable, because yeasts weren’t able to transform the brown algae’s alginate and mannitol to bio-ethanol. Now the team, under Yasuo Yoshikuni from Bio Architecture Lab Inc. (Berkeley, USA) and the biofuel firms BALChile SA (Santiago de Chile) and Statoil ASA (Trondheim, Norway), have presented a metabolically-engineered yeast strain that can achieve that.
After re-engineering the alginate and mannitol catabolic pathways in the standard industrial microbe Saccharomyces cerevisiae, researchers also integrated the alginate monomer (4-deoxy-L-erythro-5-hexoseulose uronate, or DEHU) transporter from the alginolytic eukaryote Asteromyces cruciatus into the yeast genome.
Overexpression of the transporter gene together with the required bacterial alginate and deregulated native mannitol catabolism genes, enabled S. cerevisiae to efficiently metabolise DEHU and mannitol.
When this platform was further adapted to grow on mannitol and DEHU under anaerobic conditions, it was capable of ethanol fermentation from mannitol and DEHU, achieving titres of 4.6%(v/v) (36.2 g l21) and yields up to 83% of the maximum theoretical yield from consumed sugars.
According to the researchers, these results show that all major sugars in brown macroalgae can be used as feedstocks for biofuels and value-added renewable chemicals in a manner that is comparable to traditional arable-land-based feedstocks.
The research is reported in Nature