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, Pl euronema sp. and Fabrea salina, was examined following growth on eithe r an algal or bacterial diet. When allowed to feed on a natural bacter ial community, Pleuronema sp. synthesized the triterpenoid alcohol gam maceran-3 beta-ol (tetrahymanol) and two hopanoids (hopan-3 beta-ol an d one uncharacterized hopanoid). When fed the marine alga Isochrysis g albana, F. salina contained the major algal sterol 24-methylcholesta-5 , 22-dien-3 beta-ol and several long chain ketones specific to the alg a. In both ciliates, fatty acids composition showed a general correspo ndence to that of the diet. Using a series of antibiotic treatments to alter the bacterial prey community, and thus fatty acid composition o f the ciliate's diet, promoted changes in the fatty acid composition o f Pleuronema sp. to resemble that of the bacterial prey. The addition of a mixture of algal sterols to a bacterized culture of another scuti cociliate, Parauronema acutum, inhibited tetrahymanol synthesis and re sulted in the incorporation of sterols into the ciliate.