Amethystin, the Coloring Principle of Stentor amethystinus

Abstract

Among the ciliates, Stentor amethystinus stands out for its conspicuous red-violet color compared to its blue- and red-colored relatives Stentor coeruleus and Blepharisma japonicum. Rich blooms in German lakes allowed us to collect sufficient organisms to isolate the pigments and elucidate the structure of the main component amethystin (4) by spectroscopic methods as a carboxy derivative of blepharismin. Depending on conditions, the carboxy group appears as an orthoester or as a mixture of the orthoester and small amounts of a hydroxylactone. Derivatives of both isomeric forms were obtained by acetylation and methylation supporting the proposed structures. On reaction of amethystin with base in the presence of oxygen, oxyamethystin and, under vigorous conditions, p-hydroxybenzoic acid were formed. In addition to 4, two homologues, an isomer of amethystin, and stentorin F (1b) were identified in the primary extract. Further, a biosynthetic scheme is proposed linking stentorin, blepharismin, and amethystin type compounds to the hypothetical protostentorin as a common intermediate.

Predator-Prey Interactions in Ciliated Protists

“…Summarizing, the Blepharisma species studied are able to defend themselves against C. hirtus, although S. sphagnetorum and S. roeseli seem to overcome Blepharisma's chemical defense, but it was observed that after the ingestion of intact cells of the toxic ciliates these predators are not able to reproduce, suggesting the presence of the post-ingestion toxicity phenomena [56]. Additional toxic pigments, structurally related to hypericin, were found in other heterotrich ciliate species, such as stentorin in S. coeruleus (see [57] for a review), amethystin in S. amethystinus [58], and maristentorin in the marine ciliate Maristentor dinoferus [59], but the defensive function was experimentally proved only for S. coeruleus [60].…”

Cold‐shock based method to induce the discharge of extrusomes in ciliated protists and its efficiency

“…In other studies, the secondary metabolites produced by a ciliate were simply analyzed after rough cell extractions, generally using organic solvents. However, through this procedure, information about the original cell localization of the analyzed substances was lost and not always deducible .…”

Metabolites from the Euryhaline Ciliate Pseudokeronopsis erythrina

“…Blepharismins and stentorins are both characterized by a hypericin‐like skeleton. Similar compounds have been recently isolated, including maristentorin from the marine ciliate Maristentor dinoferus 15 and amethystin from the freshwater ciliate Stentor amethystinus 16…”