Genetic Modification of Plant Biomass for Biofuel production

Genetic modification, a genetic engineering process is simply the manipulation of the gene to alter the genetic makeup of the organisms for the selection of desired characteristics or traits (Pyne et al., 2011). This technology came into effect with the development of recombinant DNA technology (Regina, 2015) which has improved the quality of human life and the environment over the years. Whether it is the synthesis of biochemicals or utilizing plant biomass or other organic wastes for bioenergy and biofuel production, genetic modification has made a significant impact on green recovery.

The increasing demand for sustainable green energy and the negative consequences, such as global warming and energy insecurity of fossil fuels have triggered the sustainable supply and production of plant biomass. With the application of gene manipulation, it has become possible to revolutionize the plant biomass yield and conversion efficiency to biofuel. Therefore, the genetic modification technology has the potential to make a significant impact in the global green energy transition by altering the characteristics and properties of lignocellulosic (plant dry matter) biomass, oil, sugar, and starch crops and transform into desired bioenergy or biofuel resources.

Biofuels are generally produced from the biomass of first- and second-generation energy crops. The first-generation biofuel includes the most common conventional energy, bioethanol, and biodiesel deriving from sugar (sugar cane and sugar beet), starch (corn, wheat, and potato), and oil (sunflower, soybean, and rapeseed). The feedstocks are associated with direct food versus fuel competition. Hence to overcome this issue, the lignocellulosic biomass is utilized to produce second-generation biofuel (Davidson, 2008). Most of this biomass consists of woody, non-edible parts of plants. The agricultural residues of rice and wheat straw, corn stover, grass plant residue, and bagasse are the most common source of lignocellulosic biomass. This resource is already the by-product and therefore, reduces the competition between the land for fuel and food production.

Composition of lignocellulosic biomass

Lignocellulosic biomass mainly consists of three main components: cellulose, hemicellulose, and lignin and pectin as a minor component. Cellulose is a crucial polysaccharide that signals cells to grow and connects cells to form tissues. Hemicellulose contributes to strengthening the cell wall by interaction with cellulose. Lignin acts as a natural defense against pathogens and provides structure to the plant. Cellulose, which is insoluble in water, is the main component in lignocellulosic biomass.

Genetic modification of plant biomass

As mentioned above, the challenge of using lignocellulosic biomass is that the cellulose gets bonded with hemicellulose and lignin. The fermentation process for hemicellulose becomes more complicated than cellulose. As a result, the production of biofuel from lignocellulosic and other plant biomass by the conventional process is expensive, not-feasible for commercial scale, and requires advanced technology.

Therefore, the third-generation biofuel crops including microalgae and seaweed are utilized as alternative biomass. Further, to ease the process and reduce the cost of biofuel production, gene modification comes into play. This is known as fourth-generation biofuel crops that involve genetically modified biomass.

In the fourth-generation biofuel production, the plant biomass is modified genetically as desired to take high carbon contents or other essential products that can be easily converted into biofuels. After gene modification, the plant biomass can secrete the cellulase and hemicellulase enzymes that can degrade the cellulose and hemicellulose. This conversion route is called enzymatic hydrolysis. Otherwise, the biomass is treated with a complicated thermochemical process at high temperature and pressure to disintegrate the long-chain and complex carbon molecules.

After the disintegration, the conversion efficiency of the downstream process can also be improved by using genetically modified enzymes. Finally, the fermentation process followed by the distillation process converts monomeric sugars into pure biofuel (Davidson, 2008; Fatima et al., 2018).

Applications of genetically modified plant biomass

The concept of genetic engineering has enormous potential in stable and high yield biomass production and conversion efficiency of biomass. The challenge for lignocellulosic biomass deconstruction becomes natural with genetic engineering by modifying lignin to reduce the biomass pre-treatment processes and conversion costs, manipulating crops to develop varieties with increased polysaccharides (C₆ chains) and fewer lignin levels, and improving plant biomass to produce cellulase and hemicellulase enzymes on its own.

Gene manipulation can play a significant role to harness improved crop yields and overcome abiotic stress to balance the food and fuel competition. The genetic modification of crops, such as tobacco, alfalfa, corn, and rice enhances biomass quality and yields, and the future seems promising (Sticklen, 2008; Chen and Dixon, 2007).

Moreover, a plant with nitrogen-fixing capacity and that which consumes less water with high biomass yields, and conversion efficiency to biofuels is possible with genetic modification (Furtado et al., 2014). Moreover, the non-seed plant produces oil in leaves, stems, and other non-seed parts of plant biomass after gene manipulation. Also, the main ingredients used in biodiesel, such as bio-based lubricants and esterified fatty acids, can be bioengineered from oilseed crops such as Jatropha (Akashi and Nanasato, 2018).

C₄ grass (4 carbon sugar, warm-season grass), such as napier grass (Pennisetum purpureum), sorghum (Michanthusgiganteus), and switchgrass (Panicum virgatum) and the C₃ (3 carbon sugar, cool-season grass) plant species like poplar, aspen, and willow are considered the best source of biomass for biofuel production. Gene manipulation of the C4 and C3 grass boost the yield of biomass. The genomic investigation in biomass is widespread in the United States, Europe, and Brazil (Brandon and Scheller, 2020).

Biswal et al. (2015) reported that the significant improvements in the biomass with the suppression and elimination of various genes aids in the synthesis of specific polysaccharides. Various kinds of polysaccharide biosynthesis involve cellulose, hemicellulose, and pectin modification. Similarly, the ideal bioenergy crop content is the result of increased cellulose biosynthesis as it contains a C6 sugar molecule. Also, the co-overexpression of specific genes that codes for an enzyme increase the galactose content by 80% in Arabidopsis (Brandon and Scheller, 2020). The pectin modification by overexpression of the pectate lyase gene resulted in improved saccharification (Biswal et al., 2015).

Conclusion

In a nutshell, the concept of plant genetic modification has a remarkable possibility in meeting the biofuel demand of the world. It acts as an alternative way to mitigate the carbon footprint and proceeds in a sustainable way to abridge the dependency on fossil fuels. Genetic modification of plant biomass allows the significant change in gene to produce the desired quality and volume of biomass in a short period. Numerous studies are going on, and researchers continue to look for solutions to the global energy crisis as plant gene recombination acts as a doable alternative.

The manipulation of plant genes converts the plant biomass to biofuel or bioenergy, and this could optimize the resources available to meet the affordable energy demand in an environment-friendly manner. With regulatory frameworks designed and participation of private and public sectors in putting plant gene modification as an agenda for biofuel, the environment can prolong and adds value in the global energy mix.

For citation: Ghimire, A. and Poudel, R. C. 2020. Genetic modification of biomass for biofuel production. Biomass Feedstock, www.greenesa.com