MARINE CILIATES AS A WIDESPREAD SOURCE OF TETRAHYMANOL AND HOPAN-3-BETA-OL IN SEDIMENTS

We observed tetrahymanol (gammaceran-3-beta-ol) as a principal neutral lipid in eight marine ciliate species, most of which were scuticociliates, a group of ciliates that feeds mainly on bacteria. Tetrahymanol abundance in pure cultures and field samples (sediment traps, water column particulates, and enrichments from coastal and estuarine environments) shows good agreement with ciliate biovolume (R2 = 0.89), suggesting that tetrahymanol is a specific marker for marine ciliates that feed on bacteria. Hopan-3-beta-ol was also positively identified in several ciliates, but did not occur in all species examined. Because of their widespread distribution in modern marine systems, these organisms provide a likely source for the common appearance of tetrahymanol in many marine sediments. By analogy, the presumed presence of ciliates in ancient seas may explain the occurrence of its diagenetic product, gammacerane, in more mature sediments and crude oils.