Review and Outlook of Fourth-Generation Biofuels: Genetically Engineered Microalgae at the Nexus of Technology, Sustainability, and Policy Challenges

Genetically engineered microalgae with enhanced light-use efficiency, productivity, and intracellular biofuel (lipid) content can be used for the generation of fourth-generation biofuels (FGBs). This approach not only improves the output of biofuel but also the resource efficiency. The use of genetically modified (GM) algae as a feedstock for biofuel production on a commercial scale will raise significant environmental and ecological biosafety concerns that need to be addressed. Some of these issues include the accidental release of modified organisms, horizontal gene transfer, and human health implications, as well as safe disposal of the process byproducts. Therefore, a comprehensive assessment of the technical, environmental, and regulatory challenges associated with these systems is necessary. While progress has been made in developing novel genetic and biotechnological approaches to improve algal productivity, fewer efforts have been directed toward examining the regulatory framework that governs the cultivation and processing of GM microalgae. This paper reviews the current legislation and biosafety regulations together with mitigation strategies for risk with respect to FGB production. Open pond cultivation systems are still considered the most cost-effective means for producing microalgae on a large scale. However, the risks of environmental escape and impacts on human health coupled with strict regulatory oversight are major hurdles to commercialization. The handling of process residues, such as solid byproducts and residual wastewater, can carry a risk of residual plasmid or chromosomal DNA transfer. Data reported for field-scale studies of GM microalgae cultivation in open environments indicate that when appropriate containment and regulatory measures are implemented, consistent adverse environmental effects do not occur, and there have been no confirmed cases of gene transfer. These findings indicate that genetically engineered microalgae can provide a safe and sustainable platform for the production of FGB provided that appropriate regulatory compliance and mitigation measures are executed.