Conversion of minimally processed Sargassum to lipids with the yeast Rhodosporidium toruloides

The conversion of brown macroalgae like Sargassum offers a secure route for biofuel production from an abundant and underutilized biomass resource; however, efficient utilization of this feedstock remains a major challenge. This study explores the feasibility of converting unwashed and minimally processed Sargassum biomass to microbial lipids with the oleaginous yeast Rhodosporidium toruloides. Acid, alkaline, and hydrothermal pretreatments with enzymatic hydrolysis using cellulase, hemicellulase, and alginate lyase enzyme cocktails were evaluated to assess their ability to deconstruct Sargassum natans. The resulting hydrolysates were tested for the ability to support R. toruloides growth and lipid accumulation. We observed that alkaline-pretreated hydrolysates yielded higher cell growth and produced 0.08 mg of lipids per mg of dry cell weight. Lipid characterization revealed that the strain produced lipids with fatty acids predominantly comprising C16:0, C18:1, and C18:2 species, comparable to those found in vegetable oils suitable for biodiesel applications. Overall, this work establishes a basis for coupling macroalgal deconstruction with yeast bioconversion and highlights S. natans as a promising substrate for the production of fuels and chemicals.