Evaluation of Laminaria Digitata Hydrolysate for the Production of Bioethanol and Butanol by Fermentation

Abstract

Seaweeds (macroalgae) are gaining attention as potential sustainable feedstock for the production of fuels and chemicals. This comparative study focuses on the characterization of the microbial production of alcohols from fermentable carbohydrates in the hydrolysate of the macroalgae Laminaria digitata as raw material. The potential of a hydrolysate as a carbon source for the production of selected alcohols was tested, using three physiologically different fermentative microbes, in two main types of processes. For the production of ethanol, Saccharomyces cerevisiae was used as a benchmark microorganism and compared with the strictly anaerobic thermophile Thermoanaerobacterium strain AK17. For mixed production of acetone/isopropanol, butanol, and ethanol (A/IBE), three strictly anaerobic Clostridium strains were compared. All strains grew well on the hydrolysate, and toxicity constraints were not observed, but fermentation performance and product profiles were shown to be both condition- and strain-specific. S. cerevisiae utilized only glucose for ethanol formation, while strain AK17 utilized glucose, mannitol, and parts of the glucan oligosaccharides. The clostridia strains tested showed different nutrient requirements, and were able to utilize glucan, mannitol, and organic acids in the hydrolysate. The novelty of this study embodies the application of different inoculates for fermenting a common brown seaweed found in the northern Atlantic Ocean. It provides important information on the fermentation properties of different microorganisms and pinpoints the value of carbon source utilization when selecting microbes for efficient bioconversion into biofuel and chemical products of interest.

Biotechnological Prospects of Thermoanerobacter AK15: End-Product Formation from Carbohydrates, Amino Acids, and Lignocellulosic and Macroalgae Hydrolysates

“…A report by Wang et al used Gracilaria salicornia , an invasive brown algae, to achieve a modest ethanol titer of 1.57 g/L using E. coli strain KO11 (ATCC 55124) [ 54 ]. A recent investigation of the fermentation of Laminaria digitata hydrolysates, pretreated with enzymatic hydrolysis, showed 0.30 gg −1 of consumed substrate (59% of theoretical yields) [ 55 ].…”

Metabolic engineering of Thermoanaerobacterium AK17 for increased ethanol production in seaweed hydrolysate

“…Thermoanaerobacterium AK17 was previously shown to be able to grow on a L. digitata hydrolysate, where it consumed glucose, mannitol, and part of the glucan fraction, while producing ethanol and organic acids [ 29 ]. In this study, the ethanologenic strain AK17_M6 was used to ferment the same hydrolysate and its performance was compared to the performance of the wild-type strain.…”

“…The sugar residues of hemicellulose also contain a varying mixture of hexoses (e.g., glucose, mannose, galactose) and pentoses (e.g., arabinose and xylose). Strain AK17 was previously shown to utilize all of these residues, and also pectin polymers [ 25 , 27 ], as well as oligosaccharides of β-1,3 glucans as a carbohydrate source [ 29 ]. These results highlight that the newly engineered strain AK17_M6 could be used to produce ethanol from both second and third generation biomass, making it an efficient and versatile fermentative microorganism producing only ethanol from a variety of substrates.…”

“…End-products were ethanol, acetate, lactate, and hydrogen, with a maximum ethanol yield of 1.5 mol/mol of glucose (75% of the maximum theoretical yield). Recently, the strain was also evaluated for its potential to ferment seaweed hydrolysate to produce bioethanol [ 29 ].…”

Biotechnological prospects of Thermoanaerobacter AK15; end-product formation from sugars, amino acids, lignocellulosic and macroalgae hydrolysates

“…Similarly, high yields have been obtained from red and brown macroalgae species ( [36], and references therein). Recent investigation of the fermentation of Laminaria digitata hydrolysates, pretreated with enzymatic hydrolysis showed 0.30 gg -1 of consumed substrate (59% of theoretical yields) [37].…”