Antimicrobial activity of euplotin C, the sesquiterpene taxonomic marker from the marine ciliate Euplotes crassus

Abstract

Strains of the marine ciliate protist Euplotes crassus produce exclusive terpenoids called euplotins that play an ecological role. Among these derivatives, euplotin C is the main of four secondary metabolites isolated from cultures of this protozoon and represents the sesquiterpene taxonomic marker from E. crassus. Because different terpenoid metabolites of plant origin showed a certain antimicrobial activity, we assessed the compound euplotin C, purified by high-pressure liquid chromatography and solubilized in two solubility enhancers, against the protozoa Leishmania major and Leishmani infantum, the fungus Candida albicans, and nine strains of gram-positive and gram-negative microorganisms. An activity of euplotin C against Leishmania promastigotes was demonstrated (50% lethal doses were 4.6 or 8.1 microg/ml depending on the agent used to solubilize the compound), while the effect was less evident on Candida and nearly absent on bacteria. A nonsignificant cytotoxicity (50% lethal dose, >200 microg/ml) against the J774 cell line was observed. A leishmanicidal activity was also shown by the living, euplotin-producing cells of E. crassus cultured together with promastigotes; this activity increased with time from 10 min to 6 h of incubation. This study provides an initial rationale for the evaluation of euplotin C and other similar natural products as alternative or possibly synergistic compounds for current antiprotozoon chemotherapeutics.

FIG. 1.

Chemical structure of EC, the compound used in this study.

FIG. 2.

Inhibitory effects of EC complex 1 (at 100 and 20 μg/ml) and the solvent DMSO (at 0.1 and 0.02%) on the growth of L. major and L. infantum after 2, 24, and 48 h of contact. Percentages were calculated relative to the growth of promastigotes in medium, considered as 100%.

FIG. 3.

Inhibitory effects of EC complex 1 and DMSO (A) and of EC complex 2 and DIMEB (B) on the growth of E. vannus strain TB6.

FIG. 4.

Effects of the two Euplotes strains on the viability of L. major and L. infantum. (A) E. crassus strain SSt22 (euplotin-producing strain); (B) E. vannus strain TB6 (non-euplotin-producing strain). The Euplotes strains remained viable for the duration of the experiment.