Current knowledge of the starvation and reproduction stages of the limnic species Holophrya teres (Ciliophora: Prostomatea)

How Ciliated Protists Survive by Cysts: Some Key Points During Encystment and Excystment

Forming cysts is a common and important bionomic strategy for microorganisms to persist in harsh environments. In ciliated protists, many species have been reported to form cysts when facing unfavorable conditions. Despite traditional studies on the morphological features of cysts and the chemical composition of cyst wall, recent research has focused more on the molecular mechanisms of encystment. The present work reviews studies on developmental features and molecular information of resting cysts in ciliates, and pays more attention to the following questions: what are the inducing factors of encystment and excystment? How does the cell change morphologically during these dynamic processes? And what molecular mechanisms underlie those changes? We also present and summarize the characteristics of cysts from diverse ciliate lineages in a phylogenetic framework, aiming to provide new perspectives for studies on adaptive evolution of unicellular eukaryotes.

Infection of Slugs with Theronts of the Ciliate Protozoan, Tetrahymena rostrata

Tetrahymena rostrata is a free-living ciliated protozoan and is a facultative parasite of some species of terrestrial mollusks. It is a potential biopesticide of pest slugs, such as the grey field slug, which cause considerable damage to crops. T. rostrata has several developmental forms. Homogeneous preparations of the feeding stage cells (trophonts) and excysted stage cells (theronts) were compared for their ability to infect and kill Deroceras reticulatum slugs. Theronts were more effective and remained viable and infective, even after prolonged starvation.

A detailed description of a Brazilian Holophrya teres (Ehrenberg, 1834) and nomenclatural revision of the genus Holophrya (Ciliophora, Prostomatida)

I studied a Brazilian population of Holophrya teres (Ehrenberg, 1834) Foissner, Berger and Kohmann, 1994, using live observation, morphometry, silver impregnation, and scanning electron microscopy. This showed a fair similarity with European populations, especially in having a large (about 13 × 5 μm in vivo) micronucleus pyriform in broad-side view and cuneate in narrow-side view. Several new structures were discovered, viz., an internal oral basket, teeth on anterior end of the oral basket rods, and a buccal seal closing the oral basket when not feeding. Based on this knowledge, I provide an improved diagnosis for H. teres, which can be used as template in further species descriptions. Depending on brosse implantation in the somatic ciliature, the genus was split in Holophrya, Hillerophrya nov. gen., Vdacnyophrya nov. gen., and Bardeleophrya nov. gen. Twenty-one Prorodon species were combined with the holophryid genera, using brosse and thick oral basket rods as main markers. This revealed two new species, viz., Holophrya longiarmata nov. spec. and H. agamalievi nov. spec.