Plant, Microbial And Algal Biotechnology For A Clean Energy Future

As global energy demand rises and pressure to decarbonise intensifies, biotechnology is emerging as a key driver of sustainable fuel innovation. In this Insight, we explore how advances in plant, microbial and algal biotechnology can support the transition to cleaner energy systems and contribute towards meeting United Nations Sustainable Development Goal 7:Ensure access to affordable, reliable, sustainable and modern energy for all.

Biofuels

Plant, microbial and algal biotechnology is playing an increasingly important role in the development of sustainable and renewable energy sources. Biofuels are renewable energy sources that have the potential to offer lower-carbon alternatives to fossil fuels.

First-generation biofuels use edible crops for the production of bioethanol and biodiesel. However, the use of edible crops sparked a food versus fuel debate, and there is ongoing concern as to whether such biofuels can truly be sustainable if farmland is diverted away from food production. Nevertheless, second-, third- and fourth-generation biofuels offer potential routes to reducing reliance on fossil fuels.

Engineering enzymes and plant cell wall architecture

Second-generation biofuels are derived from non-food crops, or food waste, high in lignocellulosic biomass (i.e. containing high amounts of lignin, cellulose and hemicellulose). Cellulose is a structural component of the plant cell wall and the predominant carbohydrate in lignocellulosic biomass. It is a polymer of glucose and provides a source of sugars for fermentation to biofuels. However, cellulose can be difficult to access and degrade because of its crystalline microfibrillar organisation and its association with other cell-wall components. Industrial processing of lignocellulosic biomass relies on enzymes that break down the different components of the cell wall. For example, cellulose is broken down into its constituent sugars by the coordinated action of endoglucanases, exoglucanases and beta-glucosidases, whilst xylan-rich hemicellulose can be hydrolysed by xylanases and associated enzymes to release fermentable sugars including xylose. Research into the breakdown of the plant cell wall has been integral to improving lignocellulosic biofuel production.

The fungus Trichoderma reesei offers a source of cellulolytic enzymes that can be used for lignocellulosic biomass degradation. These enzymes have been engineered to improve thermostability and pH tolerance, enabling their use in enzyme cocktails under industrial conditions. The T. reesei strain RUT-C30 has also been engineered using CRISPR/Cas9 to provide a platform to secrete these cellulolytic enzymes for industrial application.

Metagenomic sequencing can also aid the discovery of new enzymes for lignocellulose degradation. A metagenomic analysis of soil samples in Brazil identified a unique bacterial copper-dependent redox enzyme (CelOCE) that oxidatively cleaves cellulose to cellobionic acid. Expression of CelOCE in Trichoderma reesei enhanced cellulose saccharification, increasing glucose release from pretreated lignocellulosic biomass by around 20%.

In addition, genetic engineering technologies can improve crop characteristics to reduce the recalcitrance of the cell wall to enzymatic degradation. Switchgrass is a prime lignocellulosic feedstock. Overexpression of the rice BAHD acetyltransferase enzyme OsAT10 in switchgrass has been shown to alter the relative levels of p-coumaric acid and ferulic acid modifications on hemicellulose. The resulting decrease in ferulic acid content increased the accessibility of the cell wall to degradation and boosted the release of glucose by up to 40%.

Together, enzyme and microbial engineering are improving the efficiency of industrial lignocellulose degradation, while genetic modification of feedstocks can make plant cell walls inherently more amenable to processing. A fundamental understanding of plant biochemistry therefore underpins potential improvements for second-generation biofuel production.

Engineering algal and microbial biotechnology

Algae offer an alternative source of biomass for the production of third-generation biofuels. They can be cultivated in wastewater and without the use of agricultural land. In addition, some microalgae have a high lipid content (15–60% of dry weight), providing a potential feedstock for biodiesel production. Lipid accumulation can also be induced by environmental stresses such as nutrient limitation.

Recent research has demonstrated that microalgal species may be engineered using CRISPR/Cas9 genome editing to increase their lipid content. Disruption of the omega-3 fatty acid desaturase (fad3) gene in Chlorella vulgaris and increased expression of malic enzyme in Phaeodactylum tricornutum have both been shown to increase lipid content. Such genetically engineered microalgal strains therefore show promise for increasing lipid yields for biodiesel production.

An alternative approach for fourth-generation biofuel production is the reconstitution of metabolic pathways in organisms that are readily genetically manipulated, such as Escherichia coli and Saccharomyces cerevisiae (baker’s yeast). Such organisms have been used to produce ethanol and butanol and offer genetically tractable platforms for biofuel production.

Innovation for a cleaner future

As global demand for energy increases, balancing energy production and land use with the global food supply is essential. Enzyme engineering, plant biotechnology and metabolic engineering are helping to develop solutions for more sustainable energy production. These innovations have the potential to deliver environmental benefits while creating commercial opportunities for agribusinesses, researchers and biotech investors, helping to drive continued innovation in energy production.

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