Lipid composition of the marine ciliates Pleuronema sp. and Fabrea salina: Shifts in response to changes in diet

The composition and incorporation of lipids in two marine ciliates, Pleuronema sp. and Fabrea salina, was examined following growth on either an algal or bacterial diet. When allowed to feed on a natural bacterial community, Pleuronema sp. synthesized the triterpenoid alcohol gammaceran-3 beta-ol (tetrahymanol) and two hopanoids (hopan-3 beta-ol and one uncharacterized hopanoid). When fed the marine alga Isochrysis galbana, F. salina contained the major algal sterol 24-methylcholesta-5, 22-dien-3 beta-ol and several long chain ketones specific to the alga. In both ciliates, fatty acids composition showed a general correspondence to that of the diet. Using a series of antibiotic treatments to alter the bacterial prey community, and thus fatty acid composition of the ciliate's diet, promoted changes in the fatty acid composition of Pleuronema sp. to resemble that of the bacterial prey. The addition of a mixture of algal sterols to a bacterized culture of another scuticociliate, Parauronema acutum, inhibited tetrahymanol synthesis and resulted in the incorporation of sterols into the ciliate.