Journal Article

Efficient ethanol production from brown macroalgae sugars by a synthetic yeast platform

Martinez, Yessica, Cooper, Susan R., Raisner, Ryan M., Santos, Christine Nicole S., Luo, Lily, Tamrakar, Pramila, Bravo, Daniel D., Peereboom, Lars, Yoshikuni, Yasuo, Tripathi, Shital A., Paredes, Carlos J., Cho, Min Y., Villari, Jeffrey L., Ohler, Nicholas L., Regitsky, Drew D., Kim, Edward J., Gill, Avinash, Hanel, Arthur, Donohoue, Paul D., Rajgarhia, Vineet, Swimmer, Candace, Bailey, Richard B., Miller, Dennis J., Enquist-Newman, Maria, Karamchedu, Padma, Lamberson, Brigit, Sarvabhowman, Preethi, Le, Chi, Goldsmith, Joshua, Kotlar, Hans Kristian, Clark, Alana, Faust, Ann Marie E.

2014

Overview

Saccharomyces cerevisiae bearing engineered alginate and mannitol catabolic pathways can ferment sugars from brown macroalgae to produce ethanol, potentially allowing the use of brown macroalgae as a viable feedstock for the production of biofuels and renewable chemicals. Brown algae as a biofuel feedstock Brown macroalgae are seen as a viable feedstock for the production of biofuels, with the advantage that they can be farmed in coastal waters without using valuable arable land. However, the most abundant sugars in brown macroalgae are alginate, mannitol and glucan, and the full potential of this feedstock cannot be realized without extensive re-engineering of the alginate and mannitol catabolic pathways in Saccharomyces cerevisiae . In this paper the authors identify a 4-deoxy-L-erythro-5-hexoseulose uronate transporter in Asteromyces cruciatus brown algae and use it to develop a S. cerevisiae strain that can use the unique sugars in brown macroalgae for high-efficiency ethanol fermentation. With appropriate genetic modifications, this synthetic biology platform can be used to produce many other biofuels and renewable chemicals. The increasing demands placed on natural resources for fuel and food production require that we explore the use of efficient, sustainable feedstocks such as brown macroalgae. The full potential of brown macroalgae as feedstocks for commercial-scale fuel ethanol production, however, requires extensive re-engineering of the alginate and mannitol catabolic pathways 1 , 2 , 3 in the standard industrial microbe Saccharomyces cerevisiae . Here we present the discovery of an alginate monomer (4-deoxy- l -erythro-5-hexoseulose uronate, or DEHU) transporter from the alginolytic eukaryote Asteromyces cruciatus 4 . The genomic integration and overexpression of the gene encoding this transporter, together with the necessary bacterial alginate and deregulated native mannitol catabolism genes, conferred the ability of an S. cerevisiae strain to efficiently metabolize 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 l −1 ) and yields up to 83% of the maximum theoretical yield from consumed sugars. 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 38/22 / 38/23 / 38/39 / 38/44 / 38/47 / 38/61 / 38/70 / 38/77 / 38/90 / 38/91 / 42/40 / 42/44 / 631/61/318 / Alcohol / Alcohol, Denatured / Algae / Alginates / Alginates - metabolism / Anaerobic conditions / Anaerobiosis / Ascomycota - genetics / Ascomycota - metabolism / Asteromyces cruciatus / Bacteria / Biodiesel fuels / Biofuels / Biofuels - supply & distribution / Biotechnology / Brewer's yeast / Carbohydrate Metabolism / Carrier Proteins - genetics / Carrier Proteins - metabolism / Enzymes / Ethanol / Ethanol - metabolism / Ethyl alcohol / Evolution, Molecular / Feedstock / Fermentation / Food / Food production / Fuels / Gene expression / Genetic aspects / Genetic Complementation Test / Genetic Engineering / Glucuronic Acid - metabolism / Hexuronic Acids - metabolism / Humanities and Social Sciences / letter / Mannitol / Mannitol - metabolism / Metabolism / multidisciplinary / Natural resources / Phaeophyceae - genetics / Phaeophyceae - metabolism / Properties / Quinic Acid - metabolism / Reproducibility of Results / Saccharomyces cerevisiae / Saccharomyces cerevisiae - genetics / Saccharomyces cerevisiae - metabolism / Science / Seaweed - genetics / Seaweed - metabolism / Sugar / Sugars / Uronic Acids - metabolism / Yeast / Yeasts