Microalgae are a promising next-generation source of feedstocks for biofuel production with the potential to serve as a practical alternative to petroleum-based transportation fuels. Depending on the microalgal species, the oils produced vary from triacylglycerols to hydrocarbons. Hydrocarbon-based fuels are preferred over other biofuels, as they are highly compatible with existing petroleum infrastructures and possess superior fuel properties.
The green microalga Botryococcus braunii is considered a promising biofuel feedstock producer due to its prodigious accumulation of hydrocarbon. It produces up to 61% of its dry weight as liquid hydrocarbon oils. These hydrocarbons are produced inside the cells of the colony, seen as intracellular oil bodies and secreted into the colony extracellular matrix where the majority of the hydrocarbons are stored. Most importantly, catalytic hydrocracking of hydrocarbons from this alga results in petroleum-equivalent fuels of gasoline, kerosene and diesel. B. braunii Race L produces the C40 tetraterpenoid hydrocarbon lycopadiene via an uncharacterized biosynthetic pathway. Despite all the advantages of B. braunii, its use for biofuel feedstock production is hindered by a slow growth rate and the lack of transformation systems to achieve targeted genetic modification. Thus, the identification of B. braunii hydrocarbon biosynthetic pathways and associated genes/enzymes can provide options for metabolically engineering these pathways into heterologous hosts with better growth characteristics and the ability to be genetically manipulated.
Researchers from Texas A&M Research identified the first committed step in lycopadiene biosynthesis in race L of B. brauniiand describe a new SSL enzyme, LOS, which carries out this reaction. Importantly, this enzyme may be used to engineer the effective production of hydrocarbon biofuel feedstocks in other photosynthetic or heterotrophic organisms in the future. This novel enzyme produces the tetraterpenoid lycopaoctaene from GGPP in a reaction analogous to that of SS. Lycopaoctaene would then undergo sequential reduction by a yet-to-be identified reductase enzyme(s) to form lycopahexaene, lycopapentaene, lycopatetraene, lycopatriene and finally lycopadiene as the major hydrocarbon product of the pathway. See the open article in Nature communications.