The review frames biofuels as a carbon-neutral proposition in principle: the carbon dioxide released when a biofuel burns is offset by the carbon dioxide the feedstock absorbed while growing. That logic underpins projections from the International Energy Agency that biofuels will supply roughly 30 percent of the renewable energy sector by 2025, with production needing to rise dramatically, from about 9.7 million gigajoules per day to 46 million gigajoules per day by 2040. But not all biofuels are created equal. The authors organize the field into four generations, each defined by its feedstock and its trade-offs, and the trajectory from first to fourth generation tells a story of steadily decoupling fuel production from food production and land use.

First-generation biofuels, derived directly from food crops such as sugarcane, corn, wheat and vegetable oils, launched the renewable fuel movement but quickly ran into the food-versus-fuel dilemma. Diverting edible crops into fuel tanks raises food security concerns, drives land-use change and can trigger deforestation and soil degradation, eroding the very climate benefits these fuels were meant to deliver. Second-generation biofuels answered part of that critique by turning to non-edible lignocellulosic biomass: agricultural waste, forestry residues, switchgrass, poplar and reed canary grass. Because this material would otherwise go to waste, the net carbon balance approaches neutrality. The technical catch is recalcitrance. Lignin resists anaerobic fermentation and must be broken down with harsh pretreatments such as alkaline peroxide, concentrated acid or organic solvents before cellulases and beta-glucosidases can hydrolyze cellulose and hemicellulose into fermentable glucose. Microbes ranging from Penicillium capsulatum to thermophilic actinomycetes and the hyperthermophile Caldicellulosiruptor saccharolyticus can degrade hemicellulose, but processing costs and seasonal feedstock variability have kept second-generation fuels from scaling.

Third-generation biofuels shift the burden from land plants to microbes, and algae have emerged as the flagship feedstock. Research on microalgae for fuel dates to the 1950s, when Ostwald and Golueke in California tested algal species in anaerobic processes. Today the appeal is easy to quantify: many microalgae accumulate 50 to 70 percent of their dry weight as lipids under optimal conditions, and some species produce 10 to 20 times more biofuel per unit area than terrestrial crops, with certain strains doubling their biomass within 24 hours. Algae cultivation is also strikingly efficient at the level of carbon accounting, fixing about 1.83 grams of carbon dioxide for every gram of biomass generated. Mixotrophic cultivation, in which algae such as Chlorella protothecoides receive both light and an organic carbon source, has shown 69 percent higher lipid production and 61.5 percent lower carbon dioxide emissions than heterotrophic approaches. Crucially, algae can grow on non-arable land, in saline or brackish water, and even in wastewater, where they strip out nitrogen and phosphorus while producing fuel feedstock.

Fourth-generation biofuels push the concept further by marrying engineered organisms with carbon capture and storage. Synthetic biology and CRISPR-based editing are being used to build microbes that convert feedstocks into fuel while sequestering carbon, and thermochemical routes such as pyrolysis, gasification and solar-to-fuel conversion are being tuned to raise hydrocarbon yields. The cyanobacterium Synechocystis has become a workhorse model because its compact genome was among the first sequenced among photosynthetic organisms, making it an ideal platform for studying and engineering oxygenic photosynthesis. These systems remain experimental, but they point toward fuels that are not merely carbon-neutral but potentially carbon-negative.

The biotechnological toolkit driving all of this is expanding rapidly. Tissue culture, for instance, allows clonal propagation of biofuel crops under controlled conditions independent of climate, and callus cultures can be manipulated to accumulate lipids. In one striking example, in vitro-grown industrial hemp callus was hydrothermally liquefied into biocrude with a petroleum-like composition, yielding 22.61 percent biocrude by weight, composed of acids, ketones, aldehydes, aromatics and hydrocarbons. Genetic engineering of microbes has delivered equally concrete gains: an engineered Escherichia coli strain expressing genes including lacZ, gapA, ldhA and pflB showed an 85 percent improvement in bioethanol production from wheat straw. A consortium of Scheffersomyces stipitis and Zymomonas mobilis increased xylose consumption by 5.52 percent and ethanol titer by 6.52 percent, and further metabolic engineering of Z. mobilis lifted xylose consumption and ethanol titer by 15.36 percent and 6.81 percent respectively. Engineered Saccharomyces cerevisiae has even co-produced ethanol and the bioplastic precursor polyhydroxybutyrate from lignocellulosic biomass.

Metabolic engineering and enzyme optimization round out the arsenal. Researchers achieved 20 grams per liter of isobutanol from cheese whey using plasmid libraries and strain improvement in E. coli, and CRISPR-Cas9 editing enabled isobutanol production in Paenibacillus polymyxa. Consolidated bioprocessing, which folds enzyme production, polysaccharide hydrolysis and sugar fermentation into a single step, cuts costs by eliminating externally supplied enzymes; the thermophilic anaerobe Clostridium thermocellum is considered a leading biocatalyst for the approach because it both degrades cellulose and produces ethanol. Extraction is being modernized too, with ultrasound-assisted and supercritical fluid techniques reducing energy and solvent use, and pyrolysis offering an economically attractive thermal route from algae to bio-oil.

Turning algae into fuel at industrial scale still requires solving a chain of engineering problems. Cultivation can proceed in open ponds, which are cheap but vulnerable to contamination, or in closed photobioreactors, which deliver higher yields and purity at higher capital cost; vertical tubular reactors exchange gases more efficiently than horizontal ones but are prone to biofilm formation. Hybrid two-stage systems offer a compromise, growing biomass first in a photobioreactor and then shifting conditions to trigger lipid accumulation. Harvesting by flocculation and filtration can recover roughly 0.1 percent dry mass per liter, and solvent extraction, including cyclopentyl methyl ether, which achieved a 39.4 percent oil extraction rate in one study, feeds into transesterification for biodiesel or fermentation for ethanol. Light, temperature, carbon dioxide concentration, pH and nutrient availability all modulate yield, with elevated carbon dioxide around 10 percent shown to boost growth and lipid synthesis by 30 to 50 percent.

The economics improve further when algae are treated as a biorefinery feedstock rather than a single-purpose crop. Beyond fuel, microalgae yield proteins exceeding 30 percent of dry weight, omega-3 fatty acids, antioxidants, pigments such as astaxanthin and beta-carotene, and bioactive compounds including the immunosuppressive agent Microcolin-A from Lyngbya majuscula and the antiviral protein cyanovirin from Nostoc. Algal sterols show anticancer and anti-inflammatory properties, and species such as Chlorella and Arthrospira are already commercialized in health foods. Algal biomass also serves as a biofertilizer: cyanobacteria fix atmospheric nitrogen and suppress soil-borne pathogens, offering a renewable alternative to synthetic fertilizers. Japan’s commercial algal production in the 1960s, which generated roughly 5,000 metric tons of dry biomass and about 1.25 billion dollars in bio-products, foreshadowed this multiproduct model.

The review’s authors are candid that significant hurdles remain, including high production costs, water and nutrient demands, resource-intensive processing, and unresolved questions about the ecological risks of releasing genetically modified microorganisms. First-generation feedstocks still dominate the industry, a practice they call unsustainable given its conflict with food security. Their prescription is continued interdisciplinary work spanning biology, engineering and economics, paired with policies and public engagement that reward genuinely sustainable practices. If those pieces align, algae-derived fuels, boosted by CRISPR-engineered strains and integrated biorefineries, could move from promising laboratory systems to a mainstream pillar of a low-carbon energy future.

Subject of Research: Biotechnological advances, including genetic and metabolic engineering, for improving algal biofuel production and environmental sustainability

Article Title: Sustainable energy solutions: the role of biotechnology and algal biofuels in environmental preservation

Article References: Kumari, S., Dalania, K., Magotra, S., Singh, A. K., & Negi, N. P. (2025). Sustainable energy solutions: the role of biotechnology and algal biofuels in environmental preservation. Discover Biotechnology, 2(1), Article 16. https://doi.org/10.1007/s44340-025-00023-0

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00023-0

Keywords: algal biofuels, biotechnology, CRISPR-Cas9, metabolic engineering, biodiesel, bioethanol, microalgae, biorefinery, carbon sequestration, lignocellulosic biomass, photobioreactors, sustainable energy