Disclosed herein are obligate heterotrophic microalgae cells containing an exogenous gene. In some embodiments the gene is a sucrose utilization gene, and further disclosed are methods of manufacturing triglyceride oils using sugar cane or sugar beets as a feedstock in a heterotrophic fermentation. In other embodiments the feedstock is depolymerized cellulosic material. Also disclosed are cells that produce medium chain fatty acids at levels not produced in non-recombinant cells of the same species and genus.