Heterologous expression of flavohemoglobin in Rhodotorula toruloides led to improved lipid production

The red yeast Rhodotorula toruloides emerged as a prominent host for microbial lipid production. It has been known that oxygen supply is a limiting factor for de novo lipid biosynthesis especially under high cell-density culture conditions. Bacterial hemoglobin is an oxygen-binding protein that can actively transport oxygen from the environment to metabolic processes. The aim of the present study was to address the problem of oxygen limitation during R. toruloides culture thereby enhancing cell growth and lipid synthesis. Thus, genes encoding flavohemoglobin (SHb) from Sinorhizobium meliloti and hemoglobin (VHb) from Vitreoscilla sp. were separately integrated into the genome of R. toruloides CGMCC 2.1389 by Agrobacterium-mediated transformation method. It was found that the engineered strain 4S-8 with SHB gene integration produced 49% more lipids under shake-flask culture condition than the parent strain. Under the two-stage culture process, the engineered strain 4S-8 produced 23% and 10% more cell mass than the parent strain and the strain 4V-10 with VHB gene integration, respectively, while the lipid titer of strain 4S-8 was 42% higher than that of the parent strain. These results suggested that heterologous expression of SHb in oleaginous hosts may be applicable for improved production of lipids and cell mass, which should facilitate more efficient conversion of sugars into lipids and fatty-acid derived biofuels.