Fatty Acid and Phospholipid Composition of the Cellular Slime Mold, Dictyostelium discoideum

Abstract

The cellular slime mold Dictyostelium dticoideum has been extensively studied (1) because of the unique series of morphological transitions that the wild type undergoes.From single, vegetative cells, the organisms pass through complex aggregation, migration, and culmination, leadii finally to spore formation.Sussmenn (2) has produced a number of stable, aggregateless mutants that remain permanently in the vegetative stage as single ameboid cells.'One of these mutants was used in the present study in order to avoid the complicating factors of morphological transition.Previous investigation of the lipids of Dictyostelium diecoideum and its aggregateless mutant Agg 204 had been limited to the characterisation of a steroid, AZ-stigmasten3&ol, and the demonstration of its biosynthesis from acetate and mevalonate (3).Stigmastenol is produced in large quantities by Dictyostelium disco&&urn and is felt to be related to the activity of the aggregation-inducing factor, acrasin (4).The fatty acids and phosphatides of the cellular slime mold are described in this paper.The fatty acid composition of each of the phosphatides has been determined.Evidence is presented for considerable molecular heterogeneity within several classes of phosphatides.The phosphatides contain an unusually high percentage of unsaturated fatty acids.Of major interest is the presence, in large amounts, of three new dienoic long chain fatty acids whose structures have been established as 5,9-hexadecadienoic acid, 5,9-octadecadienoic acid, and 5,1 l-octadecadienoic acid.Under appropriate conditions of growth, two other new fatty acids, 9-heptadecenoic acid and 5,9-heptadecadienoic acid, normally present in small amounts, can be made to accumulate.Studies of the pathways of biosynthesis of these fatty acids are presented in an accompanying paper (5). EXPERIMENTAL PBOCEDUBEGrozvth of Cells-An aggregateless mutant of Dictyostelium disco&urn,4 Agg 204, was maintained as a stock culture by clonal passage at least once every 2 weeks on SM agar (6), with a relatively penicillin-sensitive strain of Escherichia coli B/r as the substrate organism.After full growth of the amebae was permitted at room temperature, cultures were stored at 2" until used.