Engineered Yeast Makes Ethanol from Seaweed

A team of scientists from Bio Architecture Lab (B.A.L.), has developed an engineered yeast that can efficiently metabolize the sugars in seaweed and ferment them into ethanol. Bio Architecture is a California-based company focused on the production of biofuels and biochemicals from macroalgae (seaweed) with the application of synthetic biology and enzyme design.

B.A.L. scientists reported in the journal Nature the engineering of the yeast Saccharomyces cerevisiae to enable it to break down and ferment alginate and mannitol, the most abundant sugars in brown macroalgae. Conventional industrial microbes like S. cerevisiae can metabolize mannitol, but not alginate which comprises 30 to 60 percent of the total sugars in brown macroalgae. The inability of industrial microbes to catabolize alginate results in a substantial loss of product yield.

The BAL scientists integrated the gene encoding an alginate transporter from the marine fungus Asteromyces cruciatus into a S. cerevisiae strain, along with the necessary bacterial alginate and deregulated native mannitol catabolism genes. This enabled the engineered yeast strain to efficiently metabolize the alginate monomer 4-deoxy-L-erythro-5-hexoseulose uronate (DEHU) and mannitol. The yeast was capable of ethanol fermentation from mannitol and DEHU, achieving titers of 36.2 grams per liter and yields up to 83 percent of the maximum theoretical yield from consumed sugars.