Glucanocellulosic ethanol: the undiscovered biofuel potential in energy crops and marine biomass

Abstract

Converting biomass to biofuels is a key strategy in substituting fossil fuels to mitigate climate change. Conventional strategies to convert lignocellulosic biomass to ethanol address the fermentation of cellulose-derived glucose. Here we used super-resolution fluorescence microscopy to uncover the nanoscale structure of cell walls in the energy crops maize and Miscanthus where the typical polymer cellulose forms an unconventional layered architecture with the atypical (1, 3)-β-glucan polymer callose. This raised the question about an unused potential of (1, 3)-β-glucan in the fermentation of lignocellulosic biomass. Engineering biomass conversion for optimized (1, 3)-β-glucan utilization, we increased the ethanol yield from both energy crops. The generation of transgenic Miscanthus lines with an elevated (1, 3)-β-glucan content further increased ethanol yield providing a new strategy in energy crop breeding. Applying the (1, 3)-β-glucan-optimized conversion method on marine biomass from brown macroalgae with a naturally high (1, 3)-β-glucan content, we not only substantially increased ethanol yield but also demonstrated an effective co-fermentation of plant and marine biomass. This opens new perspectives in combining different kinds of feedstock for sustainable and efficient biofuel production, especially in coastal regions.

Evolutionary history of callose synthases in terrestrial plants with emphasis on proteins involved in male gametophyte development

“…Callose has been identified in some bryophytes [ 22 ] around the spore mother cell, but its link to cell-wall development, if any, is not well understood [ 2 ]. Callose is generally sparsely produced in plants, representing only 0.3–5% of the total cell-wall content ( Arabidopsis and Miscanthus [ 23 ]).…”

The effect of mechanical pre-processing and different drying methodologies on bioethanol production using the brown macroalga Laminaria digitata (Hudson) JV Lamouroux

“…This decrease is unsurprising as fermentations with the press aid alone did not generate any ethanol at detectable limits after 72 h incubation (data not shown). The leaves of M. giganteus contain 5% callose (Falter et al 2015), a β-glucan which is hydrolysable to glucose with the laminarinase used in these fermentations. However, only 17% of the harvested M. giganteus is leaf material following senescence (Costa et al 2014), so the fraction of callose from leaf material in the senesced Mean ± s.e., n = 3, no significant differences between yields in each column as determined by Tukey HSD DS = dry solids chipped material is therefore <1% of the biomass and thus could not play a significant role in ethanol generation.…”

Stover Composition in Maize and Sorghum Reveals Remarkable Genetic Variation and Plasticity for Carbohydrate Accumulation

“…Converting these carbohydrates to energy molecules has also been demonstrated in Arabidopsis ( Arabidopsis thaliana ), wherein, ectopic accumulation of triacylglycerols in vegetative plant parts was achieved by overexpression of transcription factor WRINKLED1 involved in seed oil biosynthesis (Sanjaya et al, 2011 ). There has also been considerable interest in enhancement of mixed-linkage glucans in grasses that serve as energy storage and are generally found in low amounts in grass cell walls (Buckeridge et al, 2004 ; Falter et al, 2015 ; Loqué et al, 2015 ). Variation for accumulation of non-structural carbohydrates in sorghum and maize stover supports biotechnological approaches for energy densification and development of dual-purpose (grain/stover) crops.…”