Changes in Fatty Acids During Morphogenesis in Sclerotium rolfsii

Abstract

Changes in the lipids of Sclerotium rolfsii were followed during its growth in agar and liquid synthetic media. The fungus was grown either aerobically on a cellophane membrane placed on a synthetic agar medium, or under submerged conditions in the same liquid medium, using a rotary shaker, with sclerotial formation induced by pouring the culture into Petri dishes. In the aerobically-grown fungus, lipid content decreased from 119·7 µg (mg dry wt)−1 in the mycelium to a low content of 7·4 µg (mg dry wt)−1 in mature sclerotia. The non-polar lipids were mainly utilized at the sclerotial initiation stage, while the polar lipids were utilized during sclerotial maturation. Total lipid content in submerged mycelium was 10-fold less than in aerial mycelium; however initial and mature sclerotia produced from either the submerged or aerial mycelium were similar in their lipid content and in the composition and distribution of fatty acids. Increasing glucose concentrations in the growth medium increased the fungal biomass but did not change lipid content or composition in the two growth systems. A supplement of 10−2 m-l-threonine to the growth media significantly increased the number of sclerotia produced in submerged culture. l-Threonine also prolonged the lag phase of a submerged culture and caused a delay in lipid accumulation. Moreover, l-threonine increased the lipid level but did not change the lipid or fatty acid distribution. This may help in elucidating the role of lipids in the mycelium during sclerotial formation.