Ethanol production from marine algal hydrolysates using Escherichia coli KO11
Highlights
► Acid- and hydrolytic enzyme-treatments of 4 algae produced fermentable sugars at different composition and ratios. ► Laminaria japonica hydrolysate contained a high amount of mannitol. ► Escherichia coli KO11 efficiently fermented mannitol as well as a mixture of mannitol and glucose in hydrolysate. ► E. coli KO11 and hydrolytic enzymes could be used for simultaneous saccharification and ethanol fermentation of L. japonica with high mannitol content.
Introduction
Marine alga biomass is a potential resource for biofuel production because algae can exhibit high productivity. Cultivation of marine algae would likely also not face the same food vs. biofuel issues that concern land-based biomass production (Singh et al., 2011). Compared with terrestrial plants, macroalgae (i.e. seaweeds) have a high water content of approximately 70–90%, a relatively high protein content of approximately 10%, and contain varying levels of carbohydrates (Park et al., 2008). Microalgae are comprised of 28–63% protein, 4–57% carbohydrates, and 2–40% lipids/oils by weight. Conversion of biomass from marine algae into ethanol could be economically feasible since some algae hydrolyzates can contain more total carbohydrate and hexose sugars than some terrestrial, lignocellulosic biomass feedstock (Chynoweth, 2002, John et al., 2011, Sluiter, 2006).
The purpose of this study was to investigate the effect of pretreating algae for ethanol fermentation by ethanogenic Escherichia coli KO11 (Ohta et al., 1991). We report that algal hydrolysates with a high amount of mannitol can be used as cost-effective substrates for microbial ethanol production.
Section snippets
Sources of algae and determination of their composition
Fresh brown algae, L. japonica and Sargassum fulvellum, were purchased from a seaweed market in Wando-gun, Jeollanam-do, South Korea. Dried red alga, Gelidium amansii, and green alga, Ulva lactuca, were purchased from the Agricultural and Marine Products Market at Noeun-dong, Yuseong-gu, Daejeon, South Korea. Algae were ground, sieved, and stored at −20 °C for further use.
Carbohydrate and moisture content of algae was determined using analytical methods established by the National Renewable
Analyses of algae and hydrolysates
The carbohydrate, lipid, protein and ash contents of the algae used in this study are listed in Table 1. The highest ash content was found in the brown algae S. fulvellum and the highest carbohydrate content in the red alga, G. amansii. The green alga, U. lactuca, had the highest protein and lipid content. When G. amansii was treated with 0.05–0.2 N Ca(OH)2 at 121 °C for 15 min, the formation of a gel was observed. Therefore, alkaline treatments were not pursued further in this not study. When
Conclusions
Acid hydrolysis of L. japonica biomass followed by simultaneous treatment of the lysate with hydrolytic enzymes and fermentation with ethanogenic E. coli KO11 resulted in an ethanol yield of 0.4 g ethanol/g of sugars. This yield was achievable because E. coli KO11 was able to utilize mannitol which is present in high amounts in the hydrolysate. The strategy employed could thus be a way of utilizing marine alga biomass for the production of bioethanol.
Acknowledgements
This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (MEST) (NRF-2009-C1AAA001-2009-0093062) and in part by Korean Ministry for Food, Agriculture, Forestry and Fisheries (MIFAFF).
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Present address: Samsung Petrochemical Co., Ltd.