Written by Lorenzo Mahoney '24
Edited by Surya Khatri '24
A net-zero carbon future might rely on the outside of your sushi roll. In recent years, algae have become a hot topic for scientists and governments trying to keep our world cool. In 2020, the U.S. Department of Energy invested $34 million into algal bioenergy technology projects alone [1]. Harnessing the single-celled metabolism of these photosynthesizing microorganisms has shown exciting promise in developing biofuels for more renewable and climate-conscious energy life cycles. Certain biological constraints hold the field back from widespread implementation, but genetic engineering applications are attempting to overcome these resource limitations.
Single microalgae or cyanobacteria can span 10 micrometers in size, roughly a fifth of the diameter of a human hair. Packed inside this minuscule cell, molecular machinery produces carbohydrates for nutrient and energy storage. Algal starch, which can account for the majority of an algae’s dry biomass, can be extracted and converted into bioethanol-producing sugars [2]. Their small size and high production rate make algae far and above the most efficient biofuel producer per acre compared to more commercially typical sources like soybeans and corn [3]. But the power of algal processes doesn’t stop with just sugar production: algae also produce high concentrations of fatty acids and lipids which can be harvested as fatty acid methyl esters (FAMEs), a key component of biodiesel [2].
Renewability is another major positive for utilizing algae in biofuel synthesis. The organism’s photosynthetic nature can utilize CO2 produced by harvesting mechanisms as its own energy input, lessening the greenhouse gas emissions of the total system.
This cycle creates a carbon-neutral energy system that will only improve with further advances in processing technologies. Even post cultivation and harvesting, biomass byproducts can be transformed into a variety of products. Anything from animal feed to omega-3 vitamins to fertilizer can incorporate algal residues. Here, another input-output cycle of algal cultivation emerges: biomass fertilizer can be returned to the algal system to foster continuous growth [2,4].
So, what is stopping algae from being a mainstay in renewable energy? Firstly, slotting algae into our energy economy requires a heavy investment of technological and biological assets. The newer field of algal biofuels has generated a longer time horizon for wide-scale research compared to methods developed in the previous century. More importantly, conditions that facilitate the greatest algal growth evaporate water readily and require high amounts of fertilizer and environmental nitrogen [4,5]. A 2014 report found that such reliance on nitrogen, water, and phosphorus required 53% more energy input than output, making algae far less sustainable in practice [5].
Because of the strong resource constraints, location selection is an important step in maximizing the productivity of open-pond algal growth while minimizing water and energy losses. In the United States, high-growth environments trend towards the Southern Gulf, where greater year-round temperatures and sunlight encourage the photosynthetic organisms to thrive [6]. Concerned about evaporation, analyses of water consumption factors reveal sites within the Carolinas as having more abundant water resources while still providing significant biomass growth [6]. However, East Coast locations come with the detriment of having no high-purity CO2 sources around, which would lower sites’ carbon-neutral status if carbon inputs had to be captured and transported to them, both energy-intensive steps.
As a response to the need for nearby CO2 sources, researchers have posited an environmental niche for open-pond algae alongside carbon-providing industries [7]. One example of such an industry is another biofuel processor: the corn ethanol production facilities that litter the Midwest. Research models have shown the coupling of open-pond algae with these ethanol plants can further reduce greenhouse gas emissions and fossil fuel consumption in the overall algal biofuel cycle [7]. Still, locations in Iowa and Nebraska would only be able to cultivate in the warmest months of the year, and we circle back to the climate variable. Combining the many factors in optimizing location selection, current research suggests that the most practical location to balance productivity with energy availability is in the Louisiana gulf. Here, the climate provides year-round productivity, water consumption levels are low, and in-state ammonia-production facilities generate high-purity CO2 [6,7].
Alongside location optimization, biological research has begun to focus on making the algae themselves more efficient and flexible. Modern genetic engineering tools like CRISPR-Cas9 and site-directed transformation have unlocked the potential to upgrade current algal productivity [8]. The tools target crucial genes within the algal genome to alter the metabolic rate of specific macromolecules within the cell. Take a gene like carbonic anhydrase, whose role is incorporating environmental CO2 into photosynthesis. Scientists have altered its regulation in algal genomes, and the gene’s designed overexpression has generated higher carbon capture potential in mutant strains [8]. At the same time, silencing or eliminating genes from the genome can provide a similar result. CRISPR-Cas9 has been involved in “knocking out” the phospholipase gene, a key enzyme in transforming the energy-important fatty acids and lipids into other products. With the gene removed, the lipid content of algal cells rose by 62% [9]. Genetic engineering benefits algal biofuel production by removing some of the biological barriers holding the process back, converting it to a more resource-independent source of energy.
However, what is less visible is the possible danger associated with creating a hyper-productive strain of algae. The risk of escape from open-pond environments is large and comes with the negative effects of harmful algal blooms and deoxygenation in uncontrolled environments [10]. The higher lipid production rate makes genetically modified algae nutritiously insufficient for zooplankton and can generate a cascading effect on the aquatic food web [10]. With the genetic engineering “genie out of the bag,” hyperproductive algae create a greater potential for bioenergy use. But as their efficiency increases, so too does their capability for massive environmental destabilization.
Overall, the case for algae as a renewable, carbon-neutral energy source offers exciting potential with many environmental restraints and future-thinking concerns. The ability of algae to synthesize important molecules for biodiesel and ethanol is more efficient in scale compared to current commonplace biofuel production. The cycles of CO2 uptake and conversion of biomass into fertilizer can help decrease the process’ holistic emissions to meet net-zero demands. However, algal cultivations in practice have shown a heavy demand for water and nutrients, with very few locations domestically satisfying the multitude of conditions equally. To alleviate such constraints on implementation, genetic engineers are fine-tuning algal genomes for greater cellular production of key molecules utilized in biofuel synthesis. The exciting development of hyperproductive algal strains invites the dangerous outcome of wreaking havoc on aquatic environments without heavy monitoring and careful planning. Looking toward the future, the viability of algae in energy production is uncertain, but greater research and development could transform these creatures out of the pond and into everyday energy.
References
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3. Biofuels Factsheet | Center for Sustainable Systems [Internet]. [cited 2022 Mar 4]. Available from: https://css.umich.edu/factsheets/biofuels-factsheet
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