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 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. 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.

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The effect of water on higher alcohol and noncondensable gas formation in condensed-phase ethanol Guerbet chemistry over Ni/La 2 O 3 /γ-Al 2 O 3 catalysts is investigated. Addition of 10 wt % water to anhydrous ethanol has a modest effect on conversion rate but significantly reduces both n-butanol and C 6+ alcohol yields and increases noncondensable gas yields. Removal of water formed during Guerbet condensation reactions was accomplished by installing a recirculating loop that passed the reacting solution through a bed of 3 Å molecular sieves at low temperature. Removal of reaction water further reduces gas selectivity to less than 10% and increases alcohol selectivity to greater than 75% at 50% ethanol conversion. Water present in reaction is postulated to adsorb on the nickel surface as −OH, increasing C−C bond breakage of the adsorbed acetaldehyde intermediate, and also interact with basic sites responsible for the condensation reaction, weakening their activity.

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