A First Marine Vibrio Biocatalyst to Produce Ethanol from Alginate, which is a Rich Polysaccharide in Brown Macroalgal Biomass

The use of un-utilized feedstock and seawater for material and/or energy production using marine microbial catalysts is one potential option toward contributing to the development of a more sustainable society. Ethanol production from alginate, which is an oxidized polysaccharide present in brown seaweed, is extremely difficult due to the imbalance of reducing power in the microbial cells. Production of ethanol by such means has so far been unsuccessful using marine microbial biocatalysts. To produce ethanol from alginate, an alternative pathway consisting of a pyruvate decarboxylase gene ( pdc ) and an alcohol dehydrogenase II gene ( adhII ) derived from Zymomonas mobilis strain ZM4 was implemented into a metabolically engineered bacterium, Vibrio halioticoli , which is a representative marine alginate decomposer. No ethanol from alginate was produced in the wild-type V. halioticoli ; however, the engineered V. halioticoli harboring the pdc and adhII operon (Pet operon), designated to the V. halioticoli (Pet), was able to produce 880 mg/L ethanol in maximum from 1.5% alginate for 72 h. The Pet operon also worked on the other marine alginolytic vibrios for ethanol production from alginate. This is the first case of ethanol production from alginate using marine bacterial biocatalysts under seawater-based media.