Direct bioconversion of brown algae into ethanol by thermophilic bacterium Defluviitalea phaphyphila.

Shi-Qi Ji,Ming Lu,Fu-Li Li,Bing Wang

doi:10.1186/s13068-016-0494-1

Abstract

BackgroundBrown algae are promising feedstocks for biofuel production with inherent advantages of no structural lignin, high growth rate, and no competition for land and fresh water. However, it is difficult for one microorganism to convert all components of brown algae with different oxidoreduction potentials to ethanol. Defluviitalea phaphyphila Alg1 is the first characterized thermophilic bacterium capable of direct utilization of brown algae.ResultsDefluviitalea phaphyphila Alg1 can simultaneously utilize mannitol, glucose, and alginate to produce ethanol, and high ethanol yields of 0.47 g/g-mannitol, 0.44 g/g-glucose, and 0.3 g/g-alginate were obtained. A rational redox balance system under obligate anaerobic condition in fermenting brown algae was revealed in D. phaphyphila Alg1 through genome and redox analysis. The excess reducing equivalents produced from mannitol metabolism were equilibrated by oxidizing forces from alginate assimilation. Furthermore, D. phaphyphila Alg1 can directly utilize unpretreated kelp powder, and 10 g/L of ethanol was accumulated within 72 h with an ethanol yield of 0.25 g/g-kelp. Microscopic observation further demonstrated the deconstruction process of brown algae cell by D. phaphyphila Alg1.ConclusionsThe integrated biomass deconstruction system of D. phaphyphila Alg1, as well as its high ethanol yield, provided us an excellent alternative for brown algae bioconversion at elevated temperature.

Highlights

Brown algae are promising feedstocks for biofuel production with inherent advantages of no structural lignin, high growth rate, and no competition for land and fresh water
Fermentation of glucose, mannitol, and alginate for ethanol production The growth and ethanol fermentation properties of D. phaphyphila Alg1 were evaluated by employing alginate, mannitol, or glucose as substrates
The utilization of mannitol is more complex, and has higher requirements on microorganisms. In contrast to those of Z. palmae (0.38 g-ethanol/g-mannitol) and Enterobacter sp. (0.29 g-ethanol/g-mannitol) [8, 22], D. phaphyphila Alg1 showed the highest ethanol conversion rate of 0.44 g-ethanol/g-mannitol, which suggests Alg1 is a potential strain for mannitol bioconversion

Summary

Introduction

Brown algae are promising feedstocks for biofuel production with inherent advantages of no structural lignin, high growth rate, and no competition for land and fresh water. To settle worldwide energy crisis and environmental problems, increased interests have been focused on aquatic and marine production for biofuels, which mainly includes biofuels derived from macroalgae and microalgae. Brown algae are a large group of marine seaweeds including almost 1800 species of macroalgae with a characteristic olive-green to dark brown color derived from fucoxanthin [1]. 72 % of global aquaculture-based macroalgae production, including the genera of Laminaria (reclassified as Saccharina for some species, brown algae), Undaria (green algae), Porphyra, and Gracilaria (red algae) [3]. Brown algae have complex sugar composition, mainly including alginate, mannitol, and laminarin [3]. The content of mannitol and laminarin in some species can reach as high as 25 and 30 %, respectively, at the beginning of autumn [9]

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