Effect of oxygen levels on the fatty acids and lipids of Mucor rouxii

The effect of aerobic and oxygen limiting (anaerobic) growth conditions upon the fatty acid and lipid composition of Mucor rouxii has been examined. The aerobic cells contained a range of fatty acids typical of phycomycetes, i.e. γ-linolenic acid, with an unsaturation index of 1.20, whereas the anerobic cells contained relatively high levels of shorter chained fatty acids and very low concentrations of unsaturated acids (unsaturation index=0.025). The unsaturated compounds were monoolefinic tetra-, hexa-, and octadecenoic acids; and closer examination of their di-trimethylsilyl derivatives by gas chromatography and mass spectrometry showed that all three acids contained the double bond in the Δ⁹ position. These results were consistent with a microaerobic biosynthetic pathway. In addition, there were major quantitative differences in the lipid composition of the two types of cells; and it was evident that the differences in growth environment markedly affected the cellular lipid and fatty acid compositions.