32.g: Greener Chemistry using Bioethanol and Algal Cellulose (under construction)

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Search Fundamentals of Biochemistry

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https://www.intechopen.com/chapters/79623

Algae Cellulose for bioplastics

We discussed in a previous chapter section the use of lignocelluose feedstocks from plant cell walls for the production of bioethanol. Both microalgae and macroalgae (red, green and brown) have cellulose, a β(1,4) glucose polymer in their cell walls. It is found in Chlorophyta, Dinophyta, Phaeophyta, Prymnesiophyceae, Rhodophyceae, and Xanthophyceae. There is little or much less lignin in algae, and apparently none in macroalgae. In addition, there is less hemicellulose. These characteristics make algae excellent candidates for feedstocks for third-generation bioethanol production. There are problems to overcome as well. For example, the cell wall of Glaucocystis nostochinearum is almost 90% crystalline microfibrils, which adds to its physical and chemical stability. In addition, there are other glycans in the extracellular matrix/cell wall of some algae which can make it difficult to extract and use cellulose. Extracted cellulose can also be used as a feedstock for the chemical industry as well for the synthesis of bioplastics, a topic we will consider in another chapter sections.

Algae cellulose synthesis is performed by membrane-bound cellulose synthase terminal complexes (TCs), with the geometry of the cellulose micorfibrils determined by the geometry of the TCs, as shown in Figure \(\PageIndex{1}\). Tree TCs are arranged in a hexagon with C6 symmetry, and they produced hexameric maccrofibrils.

Algal cellulose production and potential use in plasticsFig4.svg

Figure \(\PageIndex{1}\): Organization and morphology of cellulose synthesizing terminal complexes (TCs) in different organisms. Wahlström, N. et al. Cellulose from the green macroalgae Ulva lactuca: isolation, characterization, optotracing, and production of cellulose nanofibrils. Cellulose 27, 3707–3725 (2020). https://doi.org/10.1007/s10570-020-03029-5. Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/.

Figure \(\PageIndex{x}\) presents a purification flow for the preparation of cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) from rm algae biomass.

Algal cellulose production and potential use in plasticsFig6AI-01.svg

Algal cellulose production and potential use in plasticsFig6.svg

Figure \(\PageIndex{x}\): Possible conversion processes from algal biomass to nanocellulose materials. Zanchetta et al

A first purification step is required to separate cellulose from the other components of the biomass. A combination of several purification treatments can be considered depending on the biomass composition. In a second step, the cellulose can be converted to cellulose nanocrystals (CNC) or cellulose nanofibrils (CNF). A large variety of processes is available for CNF conversion. Usually the mechanical treatment can be sufficient to achieve cellulose fibrillation and CNF formation, however a pre-treatment step (biological, chemical, mechanical) can facilitate the fibrillation or in some specific cases directly achieve total fibrillation to CNF.

Wahlström, N., Edlund, U., Pavia, H. et al. Cellulose from the green macroalgae Ulva lactuca: isolation, characterization, optotracing, and production of cellulose nanofibrils. Cellulose 27, 3707–3725 (2020). https://doi.org/10.1007/s10570-020-03029-5. Creative Commons Attribution 4.0 International License, http://creativecommons.org/licenses/by/4.0/.

dkfdj Figure \(\PageIndex{x}\):

Cellulose from the green macroalgae Ulva lactuca isolation, characterization to cellulose nanofibrilsFig1.svg

Figure \(\PageIndex{x}\): Extraction protocol for the isolation of cellulose and production of CNF from Ulva lactuca

Optotracing was developed as a non-disruptive method to optically detect and visualize cellulose in biological tissues in their native states. The method utilizes optotracers, a class of molecular probes called oligothiophenes, which bind selectively to glucans producing a unique spectral pattern that identifies the bound target. Applying heptameric (Choong et al. 2018) and pentameric (Choong et al. 2019) optotracers, cellulose can be clearly distinguished from a range of glucans and glucose-containing heteropolysaccharides based on differences in size and stereochemistry. Figure \(\PageIndex{x}\):

Cellulose from the green macroalgae Ulva lactuca isolation, characterization to cellulose nanofibrilsFig8.svg

Figure \(\PageIndex{x}\): a Optotracer structures, b–e spectra patterns of optotracers fluorescence emitted when M. cellulose (green), xyloglucan (blue) and xylose (red) are interacting with b h-FTAA, c HS-310, d p-FTAA and e q-FTAA. Optotracer alone (black) is analyzed in parallel as a negative control

Biochemical Uses of Ethanol

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Bioethanol from corn and sugar cane doesn't just have to be burned. It can also be use a feedstock for chemical and biochemical synthesis reaction that would make the chemical industry greener and potentially carbon-negative.

as shown in Figure \(\PageIndex{x}\) below.

Expanding the use of ethanol as a feedstock for cell-free synthetic biochemistryFig1.svg

Figure \(\PageIndex{x}\): A possible path to a carbon-negative chemical industry. Liu, H., Arbing, M.A. & Bowie, J.U. Expanding the use of ethanol as a feedstock for cell-free synthetic biochemistry by implementing acetyl-CoA and ATP generating pathways. Sci Rep 12, 7700 (2022). https://doi.org/10.1038/s41598-022-11653-3. Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/.

Carbon is first fixed from the atmosphere into simple carbon compounds like ethanol and acetate using acetogens or electrochemistry. Cell-free synthetic biochemistry can then be used to make more complex chemicals used directly or as building block carbon chemicals. These building block carbon chemicals could then be used to build still more complex chemicals using existing or new synthetic methods. Key enabling technologies for the application of synthetic biochemistry are methods to generate a central biochemical building block, acetyl-CoA, and the biochemical energy carrier, ATP.

Here we show how ethanol can be converted with a cell free system into acetyl-CoA, a central precursor for myriad biochemicals, and how we can use the energy stored in ethanol to generate ATP, another key molecule important for powering biochemical pathways. The ATP generator produces acetone as a value-added side product. Our ATP generator reached titers of 27 ± 6 mM ATP and 59 ± 15 mM acetone with maximum ATP synthesis rate of 2.8 ± 0.6 mM/h and acetone of 7.8 ± 0.8 mM/h. We illustrated how the ATP generating module can power cell-free biochemical pathways by converting mevalonate into isoprenol at a titer of 12.5 ± 0.8 mM and a maximum productivity of 1.0 ± 0.05 mM/h. These proof-of-principle demonstrations may ultimately find their way to the manufacture of diverse chemicals from ethanol and other simple carbon compounds.

The concept starts with simple carbon compounds that can be produced with carbon fixed from the atmosphere. Advances in microbiology, metabolic engineering and electrochemistry have made possible the carbon negative production of simple one and two carbon compounds. In particular, acetogens can efficiently convert flue gas into ethanol and acetate and there are several commercial plants in development³^,4,5,6. A second development is advances in electrochemical carbon capture which can convert CO₂ into small carbon compounds like formate and ethanol with increasing efficiency⁷^,8,9,10. To the extent that the electrical power is derived from the sun or nuclear plants, electrochemistry provides another carbon negative process for making simple carbon compounds. Effective ways to upgrade these simple molecules into more complex chemicals could therefore potentially form the basis for a carbon negative chemical industry. To realize this vision of a carbon negative economy, it will be necessary to develop effective, sustainable methods for converting simple carbon compounds into more diverse chemicals¹¹. The upgraded chemicals could be used directly or employed as precursors for building additional chemical diversity, thereby replacing myriad petroleum derived chemicals with carbon negative chemicals.

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as shown in Figure \(\PageIndex{x}\) below.

Expanding the use of ethanol as a feedstock for cell-free synthetic biochemistryFig2.svg

Figure \(\PageIndex{x}\): Ethanol to acetyl-CoA module. Liu, H, ibid.

Panel (a) shows a schematic of the pathway employed. Reoxidation of NADH, catalyzed by Nox, maintains a concentration gradient to drive the otherwise thermodynamically unfavorable reaction.

Panel (b) show NADH concentration over time with different enzyme combinations as indicated in the figure.

Panel (c) shows acetyl-CoA concentration over time with different enzyme combinations as indicated in the figure.

Panel (d) shows the effect of surface area to volume on NADH concentrations over time, using the full system with ADH, ALDH and Nox. All assays experiments were performed in biological triplicates and the error bars reflect the standard deviation.

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as shown in Figure \(\PageIndex{x}\) below.

Expanding the use of ethanol as a feedstock for cell-free synthetic biochemistryFig3.svg

Figure \(\PageIndex{x}\): ATP generator module. Liu, H, ibid.

Panel (a) shows a schematic of the pathway employed. The input ethanol is converted to acetone, generating ATP in the process. The ATP can then be used separately to drive biochemical pathways.

Panel (b) shows the amount of ATP generated over time using the ATP generator module.

Paenl (c) shows the amount of acetone generated over time using the ATP generator module. All assays experiments were performed in biological triplicates and the error bars reflect the standard deviation.

as shown in Figure \(\PageIndex{x}\) below.

Expanding the use of ethanol as a feedstock for cell-free synthetic biochemistryFig4.svg

Figure \(\PageIndex{x}\): Coupling the ATP generator module to power isoprenol biosynthesis from mevalonate. Liu, H, ibid.

Panel (a) shows a schematic of the pathway employed. The ATP Generator Module supplies ATP to the two kinases required for the Isoprenol Module.

Panel (b) shows the AP amount limits the Isoprenol Module rate. The graph shows the amount of isoprenol produced by the isolated Isoprenol Module overnight as a function of the amount of AP added. To test the Isoprenol Module in isolation, ATP was supplied directly to eliminate the need for the ATP Generator Module.

Panel (c) shows isoprenol production over time by the isolated Isoprenol Module. The AP concentration was set at 7 g/L. ATP was supplied to eliminate the need for the ATP Generator Module.

Panle (d) shows optimizing the ratio of optimized ATP Generator Module enzyme concentrations to Isoprenol Module enzyme concentrations. The amount of isoprenol produced by the varying ratios after 5 h is shown as a measure of initial rate. The best ratio was found to be 1:1.

Panel (e) isoprenol production over time using the full system shown in panel a and a 1:1 ratio of ATP Generator Module to Isoprenol Module enzymes. All assays experiments were performed in biological triplicates and the error bars reflect the standard deviation.